Re: HFS/HFS+ are insecure
I think the idea that HFS+ is not used on removable device is a bit of a fallacy. I, myself, use this frequently on removable hard drives when moving large data sets back and forth from my Mac. The Mac doesn't easily read ext filesystems, but Linux can read HFS, and the various Microsoft filesystems lose too much metadata. --J > On Jan 10, 2024, at 12:39, Marco d'Itri wrote: > > On Jan 10, Michael Biebl wrote: > >> While we could ship such a udev rule for udisks, I don't think it will >> properly solve the issue. The device will still show up in nautilus, plasma >> etc and mounting is just an additional click away. > The threat model here is: somebody connects a crafted USB stick to > a computer with a locked screen. > > Also, the listed file systems are not used or not used anymore on > removable devices. > Certainly not on removable devices used by regular users. > > -- > ciao, > Marco
Re: HFS/HFS+ are insecure
On Jan 10, Michael Biebl wrote: > While we could ship such a udev rule for udisks, I don't think it will > properly solve the issue. The device will still show up in nautilus, plasma > etc and mounting is just an additional click away. The threat model here is: somebody connects a crafted USB stick to a computer with a locked screen. Also, the listed file systems are not used or not used anymore on removable devices. Certainly not on removable devices used by regular users. -- ciao, Marco signature.asc Description: PGP signature
Re: HFS/HFS+ are insecure
On Sun, 27 Aug 2023 02:34:04 +0200 Marco d'Itri wrote: So I propose this content for a file like /usr/lib/udev/rules.d/75-insecure-fs.rules: While we could ship such a udev rule for udisks, I don't think it will properly solve the issue. The device will still show up in nautilus, plasma etc and mounting is just an additional click away. The UI would have to updated to present some kind of information to the user, that mounting the FS is potentially unsafe and asking the users for extra confirmation. This would need more design work though and buy in from the desktop environments like say GNOME or KDE. Tagging such FSes via udev rules seems like a reasonable idea though. OpenPGP_signature.asc Description: OpenPGP digital signature
Re: HFS/HFS+ are insecure
On Sat, 2023-07-22 at 12:11 +, Jeremy Stanley wrote: > When the user has plugged in something that they don't realize > contains a USB storage device, perhaps because it's attached to an > internal hub within a device which has other purposes. Probably it would be a good idea for Debian GNOME to install USB Guard by default to mitigate this threat. I haven't evaluated how user friendly the GNOME management of it is though, nor whether the interface results in bad security decisions by users. With USB input devices on desktop systems, usbguard makes it easy to get yourself locked out and need to force a reboot, as I found out the hard way. -- bye, pabs https://wiki.debian.org/PaulWise signature.asc Description: This is a digitally signed message part
Re: HFS/HFS+ are insecure
On Sat, 2023-07-22 at 08:54 +0100, Matthew Garrett wrote: > When is a user going to plug in a USB stick and *not* click that button? When they found a USB stick in the parking lot, plugged it in, got the error dialog & only then remembered their company security training :) -- bye, pabs https://wiki.debian.org/PaulWise signature.asc Description: This is a digitally signed message part
Re: HFS/HFS+ are insecure
On Fri, 2023-07-21 at 18:35 +0100, Matthew Garrett wrote:
> On Fri, Jul 21, 2023 at 10:55:39AM +0200, Marco d'Itri wrote:
>
> > Unless somebody has a better idea then then my plan is to ship in the
> > next upload of kmod a file in /etc/modprobe.d/ which uses the blacklist
> > directive to prevent automatically loading some file system modules.
>
> I think this would break any existing fstab entries that reference hfs
> and hfsplus, and the convenient way to integrate Linux boot with x86
> Macs is certainly to have an hfsplus EFI partition so this may be a
> legitimate use-case. It also means that anyone who has a need to use one
> of these filesystems in a static manner is vulnerable to automount
> attacks using them.
Right, auto-loading of filesystems has to keep working. And since
mount() of arbitrary filesystems is restricted to root (CAP_NET_ADMIN
in the initial namespace), we should let the callers apply a block- or
allow-list.
The reason we have to disable auto-loading of network protocols is that
socket creation is generally an unprivileged operation, so there's no
trusted user-space that can apply the policy (besides kmod).
> Completely untested, but I think something along the lines of:
>
> SUBSYSTEM!="block", GOTO="udisks_insecure_fs_end"
> ENV{ID_FS_TYPE}=="hfs", ENV{UDISKS_AUTO}="0"
> ENV{ID_FS_TYPE}=="hfsplus", ENV{UDISKS_AUTO}="0"
> LABEL="udisks_insecure_fs_end"
>
> in a udev fragment should work? Any static fstab or mount units should
> still work, but it should disable udisks automounting regardless of the
> desktop agent involved, even if the fs modules are already loaded.
I agree we should not have UDisks probing for any of the (many) kernel
filesystems that aren't being actively maintained including responding
to security issues.
Beyond that, I would also like to see libmount limiting the filesystems
that it will probe when the fstab type is "auto". But since UDisks
normally handles mounting for unprivileged users, that's probably less
of a concern.
Ben.
--
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.
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Re: HFS/HFS+ are insecure
On 2023-07-22 08:54:59 +0100 (+0100), Matthew Garrett wrote: [...] > When is a user going to plug in a USB stick and *not* click that > button? I'm not analysing a filesystem by hand to check whether > it's trustworthy before I want it mounted. There's no reason to > automount when the screen is locked and presenting a dialog in the > case where one was plugged in and then the screen unlocked is > reasonable, but that just makes no sense as generic behaviour. When the user has plugged in something that they don't realize contains a USB storage device, perhaps because it's attached to an internal hub within a device which has other purposes. I've read about unsuspecting users buying/borrowing USB chargers and cables which contain malicious widgets designed to backdoor systems. Maybe it's urban legend because I don't personally know anyone who's said they've had machines compromised that way, and most probably target Windows/iOS/Android anyway even if they are in circulation, but since the majority of my portable computing devices charge over USB these days I try to be conscious of it and never plug into the "convenient" charging ports supplied in airports, airplanes, hotel rooms, conference rooms... I just bring my own chargers with me. Also, while the risks of hacked USB devices isn't limited to exploiting filesystem drivers (backdoored keyboards apparently also exist, for example), I tend to not configure hotplug automounting more for preference of having direct control over the system's behavior. I would much rather explicitly call the mount command and be able to decide where in the file tree it gets added, on the rare occasion that I do actually need to plug in a storage peripheral for some reason. I get that I'm probably an exception, but there are definitely users who simply find automounting behavior annoying, beyond any potential security concerns. -- Jeremy Stanley signature.asc Description: PGP signature
Re: HFS/HFS+ are insecure
On Sat, Jul 22, 2023 at 10:21:47AM +0200, Jonas Smedegaard wrote: > Quoting Matthew Garrett (2023-07-22 09:54:59) > > On Sat, Jul 22, 2023 at 03:41:58PM +0800, Paul Wise wrote: > > > Disabling auto-mounting and for manual GUI mounts, requesting users > > > confirm they trust the filesystem they are mounting would avoid that > > > as much as is reasonably possible without entirely deleting the code > > > and without breaking the use-cases of people who need the filesystem > > > code. > > > > When is a user going to plug in a USB stick and *not* click that > > button? > > When the user had plugged in a coworker's phone they were asked to please > charge. We're a long way down the social engineering chain there - I think that turns into a question of how many people are going to benefit from not automounting because of that case vs the number who benefit from the convenience under normal circumstances.
Re: HFS/HFS+ are insecure
Quoting Matthew Garrett (2023-07-22 09:54:59) > On Sat, Jul 22, 2023 at 03:41:58PM +0800, Paul Wise wrote: > > Disabling auto-mounting and for manual GUI mounts, requesting users > > confirm they trust the filesystem they are mounting would avoid that > > as much as is reasonably possible without entirely deleting the code > > and without breaking the use-cases of people who need the filesystem > > code. > > When is a user going to plug in a USB stick and *not* click that > button? When the user had plugged in a coworker's phone they were asked to please charge. - Jonas -- * Jonas Smedegaard - idealist & Internet-arkitekt * Tlf.: +45 40843136 Website: http://dr.jones.dk/ * Sponsorship: https://ko-fi.com/drjones [x] quote me freely [ ] ask before reusing [ ] keep private signature.asc Description: signature
Re: HFS/HFS+ are insecure
On Sat, Jul 22, 2023 at 03:41:58PM +0800, Paul Wise wrote: > That still potentially exposes insecure code to untrusted data, just in > a user context rather than a kernel context. The same goes for uml + > fuse + namespaces, and even guestfs VMs. You can move the data and code > to different contexts, but that doesn't change the fundamental issue. That's still a huge win! You can seccomp it, you can assign LSM restrictions, you can significantly reduce the risk associated with mounting an untrusted filesystem. We have many more controls in a user context than we do in a kernel context. > Disabling auto-mounting and for manual GUI mounts, requesting users > confirm they trust the filesystem they are mounting would avoid that as > much as is reasonably possible without entirely deleting the code and > without breaking the use-cases of people who need the filesystem code. When is a user going to plug in a USB stick and *not* click that button? I'm not analysing a filesystem by hand to check whether it's trustworthy before I want it mounted. There's no reason to automount when the screen is locked and presenting a dialog in the case where one was plugged in and then the screen unlocked is reasonable, but that just makes no sense as generic behaviour.
Re: HFS/HFS+ are insecure
On Fri, 2023-07-21 at 10:28 +, Bastien Roucariès wrote: > Long term solution will be to push under fuse these filesystem. > This a (short term)/(medium term band aid) solution. That still potentially exposes insecure code to untrusted data, just in a user context rather than a kernel context. The same goes for uml + fuse + namespaces, and even guestfs VMs. You can move the data and code to different contexts, but that doesn't change the fundamental issue. Disabling auto-mounting and for manual GUI mounts, requesting users confirm they trust the filesystem they are mounting would avoid that as much as is reasonably possible without entirely deleting the code and without breaking the use-cases of people who need the filesystem code. Of course sandboxing the code for those who need it is good too, so probably we need both, along with ways to disable the mitigations. -- bye, pabs https://wiki.debian.org/PaulWise signature.asc Description: This is a digitally signed message part
Re: HFS/HFS+ are insecure
On Fri, Jul 21, 2023 at 09:49:48AM +, Bastien Roucariès wrote: > I vaguely remember that someone implement a fuse over uml (user space linux) A similar tool is libguestfs's guestmount tool: https://www.libguestfs.org/guestfs-faq.1.html#why-don-t-you-do-everything-through-the-fuse-filesystem-interface https://www.libguestfs.org/guestmount.1.html Thanks signature.asc Description: PGP signature
Re: HFS/HFS+ are insecure
On Fri, Jul 21, 2023 at 10:55:39AM +0200, Marco d'Itri wrote:
> Unless somebody has a better idea then then my plan is to ship in the
> next upload of kmod a file in /etc/modprobe.d/ which uses the blacklist
> directive to prevent automatically loading some file system modules.
I think this would break any existing fstab entries that reference hfs
and hfsplus, and the convenient way to integrate Linux boot with x86
Macs is certainly to have an hfsplus EFI partition so this may be a
legitimate use-case. It also means that anyone who has a need to use one
of these filesystems in a static manner is vulnerable to automount
attacks using them.
Completely untested, but I think something along the lines of:
SUBSYSTEM!="block", GOTO="udisks_insecure_fs_end"
ENV{ID_FS_TYPE}=="hfs", ENV{UDISKS_AUTO}="0"
ENV{ID_FS_TYPE}=="hfsplus", ENV{UDISKS_AUTO}="0"
LABEL="udisks_insecure_fs_end"
in a udev fragment should work? Any static fstab or mount units should
still work, but it should disable udisks automounting regardless of the
desktop agent involved, even if the fs modules are already loaded.
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 10:28:00 UTC Bastien Roucariès a écrit : > Le vendredi 21 juillet 2023, 10:17:13 UTC Marco d'Itri a écrit : > > On Jul 21, Bastien Roucariès wrote: > > > > > Ok found it call mountlo outdated > > > will need a small patch for linux uml, but may be worthwhile > > > Last version seems to be outdated 0.6 and carried by slitaz distribution. > > > May be time to revive it > > It looks like a good long term solution, but as long as there are > > insecure file systems in the kernel they should be disabled by default > > so these are really different issues. > > No it is not a long term solution. Long term solution will be to push under > fuse these filesystem. This a (short term)/(medium term band aid) solution. > > I agree with you about disabling these modules > > linux uml work on i386/amd64/ppc (by memory) so it could help for some > filesystem particularly hfs > > I do not understand why uml is not part of main kernel build maybe it is time > to get it. > > The plan could be: > - build uml along the main kernel (if possible) > - try to get merged old mountlo kernel support > - push to uml only these insecure filesystem > - long term try to push these to pure userspace or drop According to the other thread only these fs should be supported using this method: - hfs (not hfs+) but pure user space tools exist -sysv -affs -ecryptfs - jffs2 - jfs - bfs - reiserfs Rouca > > What do you think ? > > rouca > > > > > I remember noise from the systemd people about mounting removable media > > using user space drivers, but I do not think that anybody is working on > > this. > > > > > > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 10:52:17 UTC Bastien Roucariès a écrit : > Le vendredi 21 juillet 2023, 08:55:39 UTC Marco d'Itri a écrit : > > efs > https://pypi.org/project/qnxmount/ claim to mount it. Check > > hfs > https://github.com/0x09/hfsfuse Corrected not supported by this package may be emulated by using user space hfs tools ? > > hfaplus > https://github.com/0x09/hfsfuse > > qnx6 > Fuse ro filesystem https://pypi.org/project/qnxmount/ better support then > kernel one > > sysv > no fuse equivalent may be easier to port from (net)?bsd source to fuse or use > the method of qnxmount > > > > affs > no fuse equivalent but a grub filesystem may be ported to fuse > > ecryptfs > no fuse equivalent > > jffs2 > no fuse equivalent > > jfs > no fuse equivalent but a grub filesystem may be ported to fuse > > > > And I think that I can also safely add a few more which while actively > > maintained I believe are only used in a retrocomputing context or are > > generally uncommon anyway: > > > > befs > A fuse module seems to be avalaible > https://www.haiku-os.org/guides/daily-tasks/access_bfs_with_fuse/ > > bfs > no fuse equivalent > > hpfs > no fuse > > omfs > https://github.com/bcopeland/omfs_fuse/ > > qnx4 > Maybe Fuse ro filesystem https://pypi.org/project/qnxmount/ > > reiserfs > so incomplete work using grub filesystem > https://github.com/albertz/reiserfs-fuse > > spu > This one is a virtual fs for powerpc should be dropped of the list > > ufs > https://github.com/mkatiyar/fuse-ufs2 > > > > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 08:55:39 UTC Marco d'Itri a écrit : > efs https://pypi.org/project/qnxmount/ claim to mount it. Check > hfs https://github.com/0x09/hfsfuse > hfaplus https://github.com/0x09/hfsfuse > qnx6 Fuse ro filesystem https://pypi.org/project/qnxmount/ better support then kernel one > sysv no fuse equivalent may be easier to port from (net)?bsd source to fuse or use the method of qnxmount > > affs no fuse equivalent but a grub filesystem may be ported to fuse > ecryptfs no fuse equivalent > jffs2 no fuse equivalent > jfs no fuse equivalent but a grub filesystem may be ported to fuse > > And I think that I can also safely add a few more which while actively > maintained I believe are only used in a retrocomputing context or are > generally uncommon anyway: > > befs A fuse module seems to be avalaible https://www.haiku-os.org/guides/daily-tasks/access_bfs_with_fuse/ > bfs no fuse equivalent > hpfs no fuse > omfs https://github.com/bcopeland/omfs_fuse/ > qnx4 Maybe Fuse ro filesystem https://pypi.org/project/qnxmount/ > reiserfs so incomplete work using grub filesystem https://github.com/albertz/reiserfs-fuse > spu This one is a virtual fs for powerpc should be dropped of the list > ufs https://github.com/mkatiyar/fuse-ufs2 > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 10:17:13 UTC Marco d'Itri a écrit : > On Jul 21, Bastien Roucariès wrote: > > > Ok found it call mountlo outdated > > will need a small patch for linux uml, but may be worthwhile > > Last version seems to be outdated 0.6 and carried by slitaz distribution. > > May be time to revive it > It looks like a good long term solution, but as long as there are > insecure file systems in the kernel they should be disabled by default > so these are really different issues. No it is not a long term solution. Long term solution will be to push under fuse these filesystem. This a (short term)/(medium term band aid) solution. I agree with you about disabling these modules linux uml work on i386/amd64/ppc (by memory) so it could help for some filesystem particularly hfs I do not understand why uml is not part of main kernel build maybe it is time to get it. The plan could be: - build uml along the main kernel (if possible) - try to get merged old mountlo kernel support - push to uml only these insecure filesystem - long term try to push these to pure userspace or drop What do you think ? rouca > > I remember noise from the systemd people about mounting removable media > using user space drivers, but I do not think that anybody is working on > this. > > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 09:49:48 UTC Bastien Roucariès a écrit : > Le vendredi 21 juillet 2023, 08:20:12 UTC Matthew Garrett a écrit : > Hi > > On Thu, Jul 20, 2023 at 07:56:12PM +0200, Marco d'Itri wrote: > > > Package: src:linux > > > Severity: normal > > > > > > You are totally correct. > > > Kernel team, please blacklist HFS/HFS+ for automounting. > > > > Isn't this a userland policy decision? udisks will happily trigger a > > module load for hfsplus if udev has identified it, and I don't think > > there's a trivial mechanism for the kernel to disable that. I believe > > the only way for the kernel to disable automounting would be to disable > > the drivers entirely (which we don't want to do), so this probably needs > > to be assigned elsewhere rather than being a linux bug. > > > > (Or, alternatively, we could move hfs(+) support to FUSE and provide > > extremely tight seccomp policies around them, and then drop kernel > > support, but even though this has been talked about a bunch I haven't > > seen anyone try to implement it) > I vaguely remember that someone implement a fuse over uml (user space linux) > > I used it last time to read in user space some crappy filesystem > > I somebody has better memory than me, it could be an idea Found it! I was mountlo > > Bastien > > > > > > >
Re: HFS/HFS+ are insecure
On Jul 21, Bastien Roucariès wrote: > Ok found it call mountlo outdated > will need a small patch for linux uml, but may be worthwhile > Last version seems to be outdated 0.6 and carried by slitaz distribution. > May be time to revive it It looks like a good long term solution, but as long as there are insecure file systems in the kernel they should be disabled by default so these are really different issues. I remember noise from the systemd people about mounting removable media using user space drivers, but I do not think that anybody is working on this. -- ciao, Marco signature.asc Description: PGP signature
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 09:49:48 UTC Bastien Roucariès a écrit : > Le vendredi 21 juillet 2023, 08:20:12 UTC Matthew Garrett a écrit : > Hi > > On Thu, Jul 20, 2023 at 07:56:12PM +0200, Marco d'Itri wrote: > > > Package: src:linux > > > Severity: normal > > > > > > You are totally correct. > > > Kernel team, please blacklist HFS/HFS+ for automounting. > > > > Isn't this a userland policy decision? udisks will happily trigger a > > module load for hfsplus if udev has identified it, and I don't think > > there's a trivial mechanism for the kernel to disable that. I believe > > the only way for the kernel to disable automounting would be to disable > > the drivers entirely (which we don't want to do), so this probably needs > > to be assigned elsewhere rather than being a linux bug. > > > > (Or, alternatively, we could move hfs(+) support to FUSE and provide > > extremely tight seccomp policies around them, and then drop kernel > > support, but even though this has been talked about a bunch I haven't > > seen anyone try to implement it) > I vaguely remember that someone implement a fuse over uml (user space linux) > > I used it last time to read in user space some crappy filesystem > > I somebody has better memory than me, it could be an idea Ok found it call mountlo outdated will need a small patch for linux uml, but may be worthwhile Last version seems to be outdated 0.6 and carried by slitaz distribution. May be time to revive it Bastien > Bastien > > > > > > > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
Hi Marco, hi, Marco d'Itri - 21.07.23, 10:55:39 CEST: > On Jul 21, Matthew Garrett wrote: > > > You are totally correct. > > > Kernel team, please blacklist HFS/HFS+ for automounting. > > > > Isn't this a userland policy decision? udisks will happily trigger a > > module load for hfsplus if udev has identified it, and I don't think > > there's a trivial mechanism for the kernel to disable that. I > > believe > > Yes, I was also thinking about this and I believe that you are right. > The kernel team did this in the past for some uncommon network > protocols, but they could do it themselves because these modules are > autoloaded using aliases. > > Since I happen to be the kmod maintainer it looks like that solving > this is on me. :-) > > Unless somebody has a better idea then then my plan is to ship in the > next upload of kmod a file in /etc/modprobe.d/ which uses the > blacklist directive to prevent automatically loading some file system > modules. […] > I think that all of these have enough of a niche usage that it would > not be an unreasonable burden for the affected users to manually load > the modules when needed (ad hoc or using /etc/modules-load.d/). In case you do this, I'd like there to be a NEWS.Debian entry about this, explaining both the justification behind it and how people can work around it. It could go like this: --- Since version xyz of kmod the file /etc/modprobe.d/block-unsafe- filesystems.conf prevents loading of several filesystem modules that are automatically loaded by udev when inserting a medium that contains one of them. These filesystems are either known to be unsafe or are not maintained actively anymore. A deliberately corrupted filesystem structure could trigger the filesystem driver in the module to crash, corrupt memory of other kernel components or to cause other problems. [Adjust to whatever risks are most likely to occur] [Add some links here for the discussion about that] In case you rely on using one or more of these filesystems you can either edit the file /etc/modprobe.d/block-unsafe-filesystems.conf and put a comment sign before the filesystem in question or add the filesystem to a file to a file in /etc/modules-load.d/. [Please clarify here as needed] Please take care not to plug in any device that you do not trust. --- This is just a rough idea it probably needs several iterations to obtain a good wording that balances on assessing the risk correctly (without over or under estimating it). Also the method of circumventing the blocking may need further explanations. I am not using systemd, so I can not describe exactly how modules-load.d works. In case you like to use any of the above wording, feel free to use it under the license of the packaging of kmod. I wonder about other kernel modules in other areas of the kernel that may be automatically loaded when connecting some hardware… especially some random USB device, but… that appears to me like opening a huge can of worms. I bet the Linux kernel has more than several hundreds of specialized USB drivers maybe even more than thousand meanwhile despite all the USB standards out there? Linux is not a micro kernel. It was not designed to run drivers in a restricted and (somewhat) safe environment to begin with. That means ideally you'd have to audit all the drivers for security issues regularly or at least after a certain amount of changes made to it. In case you do not, for some random driver it will be difficult to know for sure whether it is safe or unsafe to use. Maybe some small filesystem driver like affs that still receives a patch every now and then is safer to use than the much more complex BTRFS filesystem driver.¹ Who knows? Of cause some fuzzing may really help. But it is not a guarantee either. And then what about other kernel functionally that is loaded as module on demand that is only rarely used by some people? So I wonder what body of evidence there is to base a policy decision on which driver to load or not to load automatically. Without a reliable body of evidence there is always the risk to either over or under policy the users of Debian and derived distributions (whose maintainers do not decide to change such a policy decision again). So I'd argue against taking the quick route on that to allow the time for a more informed decision. Maybe start with clear-cut cases likely probably HFS/HFS+ instead of just adding all kinds of other filesystems without even know whether there is a known exploit. Of course you could go by maintenance status, however, this can be inaccurate. How to do accurately determine maintenance status, especially as MAINTAINERS file may not be accurate or up-to-date at all times? And how many specialized USB drivers are there that are compiled as modules on Debian kernels that may not
Re: HFS/HFS+ are insecure
Le vendredi 21 juillet 2023, 08:20:12 UTC Matthew Garrett a écrit : Hi > On Thu, Jul 20, 2023 at 07:56:12PM +0200, Marco d'Itri wrote: > > Package: src:linux > > Severity: normal > > > > You are totally correct. > > Kernel team, please blacklist HFS/HFS+ for automounting. > > Isn't this a userland policy decision? udisks will happily trigger a > module load for hfsplus if udev has identified it, and I don't think > there's a trivial mechanism for the kernel to disable that. I believe > the only way for the kernel to disable automounting would be to disable > the drivers entirely (which we don't want to do), so this probably needs > to be assigned elsewhere rather than being a linux bug. > > (Or, alternatively, we could move hfs(+) support to FUSE and provide > extremely tight seccomp policies around them, and then drop kernel > support, but even though this has been talked about a bunch I haven't > seen anyone try to implement it) I vaguely remember that someone implement a fuse over uml (user space linux) I used it last time to read in user space some crappy filesystem I somebody has better memory than me, it could be an idea Bastien > > signature.asc Description: This is a digitally signed message part.
Re: HFS/HFS+ are insecure
If an official procedure to disable the driver completely is documented and hosted from an official debian server it would be, in my opinion, an acceptable solution. Users would have a copy-pastable procedure to disable HFS if the risk is intolerable to them, sysadmin would have an official page to explain why they disabled it and having users disabling a driver might add leverage to potential effort to port this file system support out of kernel with FUSE. Le vendredi 21 juillet 2023 à 09:20 +0100, Matthew Garrett a écrit : > On Thu, Jul 20, 2023 at 07:56:12PM +0200, Marco d'Itri wrote: > > Package: src:linux > > Severity: normal > > > > You are totally correct. > > Kernel team, please blacklist HFS/HFS+ for automounting. > > Isn't this a userland policy decision? udisks will happily trigger a > module load for hfsplus if udev has identified it, and I don't think > there's a trivial mechanism for the kernel to disable that. I > believe > the only way for the kernel to disable automounting would be to > disable > the drivers entirely (which we don't want to do), so this probably > needs > to be assigned elsewhere rather than being a linux bug. > > (Or, alternatively, we could move hfs(+) support to FUSE and provide > extremely tight seccomp policies around them, and then drop kernel > support, but even though this has been talked about a bunch I > haven't > seen anyone try to implement it) >
Re: HFS/HFS+ are insecure
Looks reasonable. Le vendredi 21 juillet 2023 à 10:55 +0200, Marco d'Itri a écrit : > On Jul 21, Matthew Garrett wrote: > > > > You are totally correct. > > > Kernel team, please blacklist HFS/HFS+ for automounting. > > > > Isn't this a userland policy decision? udisks will happily trigger > > a > > module load for hfsplus if udev has identified it, and I don't > > think > > there's a trivial mechanism for the kernel to disable that. I > > believe > > Yes, I was also thinking about this and I believe that you are right. > The kernel team did this in the past for some uncommon network > protocols, but they could do it themselves because these modules are > autoloaded using aliases. > > Since I happen to be the kmod maintainer it looks like that solving > this > is on me. :-) > > Unless somebody has a better idea then then my plan is to ship in > the > next upload of kmod a file in /etc/modprobe.d/ which uses the > blacklist > directive to prevent automatically loading some file system modules. > > By looking at the MAINTAINERS file I have identified these file > systems > marked as "orphan" and "odd fixes": > > efs > hfs > hfaplus > qnx6 > sysv > > affs > ecryptfs > jffs2 > jfs > > And I think that I can also safely add a few more which while > actively > maintained I believe are only used in a retrocomputing context or > are > generally uncommon anyway: > > befs > bfs > hpfs > omfs > qnx4 > reiserfs > spu > ufs > > Did i miss anything? > > I think that all of these have enough of a niche usage that it would > not > be an unreasonable burden for the affected users to manually load > the > modules when needed (ad hoc or using /etc/modules-load.d/). >
Re: HFS/HFS+ are insecure
On Jul 21, Matthew Garrett wrote: > > You are totally correct. > > Kernel team, please blacklist HFS/HFS+ for automounting. > Isn't this a userland policy decision? udisks will happily trigger a > module load for hfsplus if udev has identified it, and I don't think > there's a trivial mechanism for the kernel to disable that. I believe Yes, I was also thinking about this and I believe that you are right. The kernel team did this in the past for some uncommon network protocols, but they could do it themselves because these modules are autoloaded using aliases. Since I happen to be the kmod maintainer it looks like that solving this is on me. :-) Unless somebody has a better idea then then my plan is to ship in the next upload of kmod a file in /etc/modprobe.d/ which uses the blacklist directive to prevent automatically loading some file system modules. By looking at the MAINTAINERS file I have identified these file systems marked as "orphan" and "odd fixes": efs hfs hfaplus qnx6 sysv affs ecryptfs jffs2 jfs And I think that I can also safely add a few more which while actively maintained I believe are only used in a retrocomputing context or are generally uncommon anyway: befs bfs hpfs omfs qnx4 reiserfs spu ufs Did i miss anything? I think that all of these have enough of a niche usage that it would not be an unreasonable burden for the affected users to manually load the modules when needed (ad hoc or using /etc/modules-load.d/). -- ciao, Marco signature.asc Description: PGP signature
Re: HFS/HFS+ are insecure
On Thu, Jul 20, 2023 at 07:56:12PM +0200, Marco d'Itri wrote: > Package: src:linux > Severity: normal > > You are totally correct. > Kernel team, please blacklist HFS/HFS+ for automounting. Isn't this a userland policy decision? udisks will happily trigger a module load for hfsplus if udev has identified it, and I don't think there's a trivial mechanism for the kernel to disable that. I believe the only way for the kernel to disable automounting would be to disable the drivers entirely (which we don't want to do), so this probably needs to be assigned elsewhere rather than being a linux bug. (Or, alternatively, we could move hfs(+) support to FUSE and provide extremely tight seccomp policies around them, and then drop kernel support, but even though this has been talked about a bunch I haven't seen anyone try to implement it)
