Bug#679377: Segmentation fault when initramfs is booting
Hi On Saturday 07 July 2012, Michael Tokarev wrote: […] On 05.07.2012 15:12, Jordi Pujol wrote: [] the patch shell-ash-export-HOME.patch causes a segmentation fault when initramfs boots, I believe that this fault occurs the first time that initramfs looks for some executable in the initramfs filesystem, Big thanks to Denys Vlasenko, the issue has been identified. […] I added a temporary workaround to this patch - making the default PATH variable to be non-const, ie, writable, this way awk will be able to write to it. No other parts of the code tries to write to it, so it is a safe change. […] Thanks a lot for your and Denys Vlasenko's efforts, this workaround in busybox 1:1.20.0-5 works fine for my use case :) Regards Stefan Lippers-Hollmann -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/201207090235.10692.s@gmx.de
Bug#679377: Segmentation fault when initramfs is booting
retitle 679377 busybox awk segfaults when called from ash and no PATH set (eg initramfs /init) tags 679377 + pending thanks On 05.07.2012 15:12, Jordi Pujol wrote: [] the patch shell-ash-export-HOME.patch causes a segmentation fault when initramfs boots, I believe that this fault occurs the first time that initramfs looks for some executable in the initramfs filesystem, Big thanks to Denys Vlasenko, the issue has been identified. awk applet, when initializes, converts environment variables into awk internal variables, and while doing this, it temporary replaces the equal sign (=) in ther with a null byte (\0). awk applet is marked as NOEXEC, ie, it is okay to run it directly from shell just by calling appropriate awk_main() routine, without executing any external program. When ash tries to run such applet, it initializes environment variables first, and calls the applet's main() function. The patch in question exports PATH variable with its default value. But this value is stored in a global CONSTANT variable (marked as const). All other exported variables are in malloc'ed memory. Also, when awk is run as a separate command, the kernel sets environment variables to be completely writable. So this very case - calling awk applet from ash when no PATH variable has been set - is the only case when ONE environment variable - PATH - is not writable. And when awk applet initializes and tries to replace = with \0, it segfaults. I added a temporary workaround to this patch - making the default PATH variable to be non-const, ie, writable, this way awk will be able to write to it. No other parts of the code tries to write to it, so it is a safe change. I can't drop this patch now, since it is too risky change at this stage in wheezy release. This rather obscure case were difficult enough to debug, and I don't want to introduce another obscure issue in some other component while wheezy is frozen. By the way, the same issue can be reproduced much, much more easily: $ env -i /bin/busybox ash -c awk Segmentation fault That was the missing part: no environment variables are set, including $PATH. Thanks, /mjt -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4ff8b03e.9030...@msgid.tls.msk.ru
Processed: Re: Bug#679377: Segmentation fault when initramfs is booting
Processing commands for cont...@bugs.debian.org: retitle 679377 busybox awk segfaults when called from ash and no PATH set (eg initramfs /init) Bug #679377 [busybox] Segmentation fault when initramfs is booting Changed Bug title to 'busybox awk segfaults when called from ash and no PATH set (eg initramfs /init)' from 'Segmentation fault when initramfs is booting' tags 679377 + pending Bug #679377 [busybox] busybox awk segfaults when called from ash and no PATH set (eg initramfs /init) Added tag(s) pending. thanks Stopping processing here. Please contact me if you need assistance. -- 679377: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=679377 Debian Bug Tracking System Contact ow...@bugs.debian.org with problems -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/handler.s.c.134169811615309.transcr...@bugs.debian.org
Bug#679377: Segmentation fault when initramfs is booting
A Dimecres, 4 de juliol de 2012 18:08:30, Michael Tokarev va escriure:
tags 679377 + moreinfo
thanks
On 28.06.2012 13:14, Jordi Pujol wrote:
Package: busybox
Version: 1:1.20.0-4
Severity: important
the patch shell-ash-export-HOME.patch causes a segmentation fault when
initramfs boots,
I believe that this fault occurs the first time that initramfs looks for
some executable in the initramfs filesystem,
Does whole thing actually work? Why do you think it is this patch
which causes the SIGSEGV? The change in this patch is quite, well,
innocent, it does not look like it can be a cause for any such issues.
This works now, using the modified version,
There are a few weeks, after the upgrade
of Busybox, the system not booted;
automatically it entered in the Busybox shell, and we see Segmentation
fault... in the file /run/initramfs/initramfs.debug
Trying the new version 1.20.1 from upstream, with their stable patches,
allways boots.
Adding the old patches to that, this little patch makes the boot fail,
I believe that some built-in Busybox commands access to internal memory tables
that are not initialized yet,
These tables may be initialized with some commands that manage paths or
directories. (It's supposed, from experiences).
Can you describe your initramfs/environment a bit? Maybe give me
access to your initramfs for testing?
my initramfs is based in Debian Live initramfs, in their mailing-list they
have been talking about that and it's solved with a workaround. This
workaround re-creates a directory (mkdir -p) that already exists.
http://lists.debian.org/CAFp4thR1VTaWJxjO1G0A--
N3ww8Mnrf3E=pe0wtye_ztexc...@mail.gmail.com
Also, the latest release of busybox, 1.20.1 is a bit different of that,
and
Different of what, exactly? The version of busybox you're
filing bugreport against is actually 1.20.1, so there are
two questions actually: what is different, and different
between what and what? -- since you're comparing the same
thing with itself.
Sorry, a detailed look shows that I was magnifying the things, there is only
one diff,
diff -Naurp ../busybox-1.20.0/shell/ash.c ../busybox-1.20.1-lnet1/shell/ash.c
--- ../busybox-1.20.0/shell/ash.c 2012-07-05 12:11:06.0 +0200
+++ ../busybox-1.20.1-lnet1/shell/ash.c 2012-04-22 03:45:24.0 +0200
@@ -6846,7 +6846,8 @@ evalvar(char *p, int flags, struct strli
patloc = expdest - (char *)stackblock();
if (NULL == subevalvar(p, /* varname: */ NULL, patloc, subtype,
startloc, varflags,
- /* quotes: */ flags (EXP_FULL | EXP_CASE |
EXP_REDIR),
+//TODO: | EXP_REDIR too? All other such places do it too
+ /* quotes: */ flags (EXP_FULL | EXP_CASE),
var_str_list)
) {
int amount = expdest - (
So, I really want to know more about your environment and
the segfault. I don't see any segfaults here.
This Segmentation fault is really difficult to debug, it's supposed that occurs
depending on the instruccions contained in every script,
Here is a saved log of an execution, using a modified Debian Live initramfs
that traps all errors,
...
+ maybe_break mount
+ [ = mount ]
+ log_begin_msg Mounting root file system
+ _log_msg Begin: Mounting root file system ...
+ [ n = y ]
+ printf Begin: Mounting root file system ...
Begin: Mounting root file system ... + . /scripts/lnet
+ export LANG=C
+ LNET_LIVEPOINT=/lnet
+ mountpoint=/lnet/image
+ LNET_MEDIA_PATH=LneT
+ LNET_LIVEVARS=/etc/lnet.vars
+ LNET_USERNAME=livenet
+ LNET_USERFULLNAME=Live never ending Tale user
+ LNET_HOSTNAME=Live-neT
+ [ -z -qb ]
+ LNET_MODPROBE_OPTIONS=-qb
+ . /scripts/functions
+ set -e
+ trap set +e ; trap - 0 ; panic Error in ${0} 0
+ touch /etc/mtab
+ mkdir -p /lnet
+ awk /MemTotal:/{print $2} /proc/meminfo
Segmentation fault...
(next the panic routine is executed...)
All the commands are built-in Busybox commands,
It has been not possible to save a log in Debian Live; in this environment
after the error the shell was locked or unresponsible,
it seems that everyone has solved this, in a form or other, change the
severity to normal, if you want.
Thanks,
Jordi Pujol
Live never ending Tale
GNU/Linux Live forever!
http://livenet.selfip.com
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Bug#679377: Segmentation fault when initramfs is booting
On 05.07.2012 04:32, Stefan Lippers-Hollmann wrote: [] I'm having trouble with the same problem in a custom (not Debian live) live boot environment, where busybox awk segfaults with shell-ash-export-HOME.patch applied. The code in question is[1]: FINGERED=$(awk -F: ' [] Executing the very same awk command from the initramfs shell (busybox ash) afterwards succeeds however: It looks like the problem only happens with awk and only when it is called as awk (not busybox awk and not /bin/awk after adding a symlink with this name pointing to busybox) and only when it is called from pid=1. For example, I did some experiments, and put a simple awk call in a separate file /at. Executing it from /init does not produce segfault, but sourcing it does (so it only happens with pid==1). I can only guess it is due to awk being NOEXEC applet. This is a problem very difficult to debug. I'll try to get something out of this all. Thank you! /mjt -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4ff5880a@msgid.tls.msk.ru
Bug#679377: Segmentation fault when initramfs is booting
tags 679377 + moreinfo thanks On 28.06.2012 13:14, Jordi Pujol wrote: Package: busybox Version: 1:1.20.0-4 Severity: important the patch shell-ash-export-HOME.patch causes a segmentation fault when initramfs boots, I believe that this fault occurs the first time that initramfs looks for some executable in the initramfs filesystem, Does whole thing actually work? Why do you think it is this patch which causes the SIGSEGV? The change in this patch is quite, well, innocent, it does not look like it can be a cause for any such issues. Can you describe your initramfs/environment a bit? Maybe give me access to your initramfs for testing? Also, the latest release of busybox, 1.20.1 is a bit different of that, and Different of what, exactly? The version of busybox you're filing bugreport against is actually 1.20.1, so there are two questions actually: what is different, and different between what and what? -- since you're comparing the same thing with itself. more upstream stable patches have been added. A new release can be packaged containing this changes, The only upstream change not included in debian package is busybox-1.20.1-mke2fs.patch, which is only relevant for busybox-static since other variants don't enable mkfs. Modifying this, busybox works fine, http://livenet.selfip.com/ftp/debian/package- modifications/busybox_1.20.1-1.lnet1.debian.tar.gz Now that's fantastic. Let's see. diff -u -p -r debian/patches/series lnet/patches/series --- 1.20.0-4/patches/series 2012-06-12 22:04:46.0 +0400 +++ lnet1/patches/series2012-06-22 19:15:34.0 +0400 @@ -1,6 +1,4 @@ -1.20.1.patch - -shell-ash-export-HOME.patch +#shell-ash-export-HOME.patch # we need to get rid of this one: #applets-fallback.patch version.patch @@ -11,10 +9,12 @@ u-mount-FreeBSD-support.patch swaponoff-FreeBSD-support.patch # FTBFS on non-linux -ps-get-uptime.patch +#ps-get-uptime.patch # upstream stable patches busybox-1.20.1-ash.patch busybox-1.20.1-ifupdown.patch busybox-1.20.1-man.patch +busybox-1.20.1-mke2fs.patch +busybox-1.20.1-ps.patch busybox-1.20.1-tar.patch So you reverted all fixes which went into 1.20.1 bugfix release, you reverted my ps-get-uptime.patch but added busybox-1.20.1-ps.patch (it has exactly the same content), added busybox-1.20.1-mke2fs.patch (which is not relevant for the issue in question), and reverted shell-ash-export-HOME.patch which looks completely innocent here, without trying to understand what it does and WHY it is here. Wherer's the improvement? This is definitely NOT a way to do things. So, I really want to know more about your environment and the segfault. I don't see any segfaults here. Thanks, /mjt -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4ff46a7e.4040...@msgid.tls.msk.ru
Processed: Re: Bug#679377: Segmentation fault when initramfs is booting
Processing commands for cont...@bugs.debian.org: tags 679377 + moreinfo Bug #679377 [busybox] Segmentation fault when initramfs is booting Added tag(s) moreinfo. thanks Stopping processing here. Please contact me if you need assistance. -- 679377: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=679377 Debian Bug Tracking System Contact ow...@bugs.debian.org with problems -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/handler.s.c.134141811716457.transcr...@bugs.debian.org
Bug#679377: Segmentation fault when initramfs is booting
Hi
On Wednesday 04 July 2012, Michael Tokarev wrote:
[…]
On 28.06.2012 13:14, Jordi Pujol wrote:
[…]
the patch shell-ash-export-HOME.patch causes a segmentation fault when
initramfs boots,
I believe that this fault occurs the first time that initramfs looks for
some
executable in the initramfs filesystem,
Does whole thing actually work? Why do you think it is this patch
which causes the SIGSEGV? The change in this patch is quite, well,
innocent, it does not look like it can be a cause for any such issues.
I'm having trouble with the same problem in a custom (not Debian live)
live boot environment, where busybox awk segfaults with
shell-ash-export-HOME.patch applied. The code in question is[1]:
FINGERED=$(awk -F: '
$1 == drive name NF 1 {
split($2, node, )
for (n in node) {
if (!system(test -b /dev/ node[n]))
cdrom[i++] = /dev/ node[n]
}
}
END {
for (c in cdrom)
print cdrom[c]
}
' /proc/sys/dev/cdrom/info)
Leading to:
Loading, please wait...
modprobe: module unix not found in modules.dep
mdadm: No arrays found in config file or automatically
Segmentation fault
Waiting for up to 30s for devices to settle...
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Segmentation fault
Failed to detect live media
modprobe: module i8042 not found in modules.dep
modprobe: module atkbd not found in modules.dep
BusyBox v1.20.1 (Debian 1:1.20.0-4) built-in shell (ash)
Enter 'help' for a list of built-in commands.
/bin/sh: can't access tty; job control turned off
(initramfs)
Executing the very same awk command from the initramfs shell (busybox
ash) afterwards succeeds however:
(initramfs) FINGERED=$(awk -F: '
$1 == drive name NF 1 {
split($2, node, )
for (n in node) {
if (!system(test -b /dev/ node[n]))
cdrom[i++] = /dev/ node[n]
}
}
END {
for (c in cdrom)
print cdrom[c]
}
' /proc/sys/dev/cdrom/info)
(initramfs) echo $FINGERED
/dev/sr0
Likewise rewriting the /proc/sys/dev/cdrom/info parsing to use
different busybox applets succeeds as well, while using awk in
different functions (fll_meminfo() and fll_copy_with_perc()) segfaults
the same way.
Can you describe your initramfs/environment a bit? Maybe give me
access to your initramfs for testing?
I'll provide a link to a test environment in a (private) follow up
mail, using this live code. While this particular initramfs hook is
not packaged in Debian, I expect similar issues to arise with standard
Debian initramfs hooks.
Also, the latest release of busybox, 1.20.1 is a bit different of that, and
Different of what, exactly? The version of busybox you're
filing bugreport against is actually 1.20.1, so there are
two questions actually: what is different, and different
between what and what? -- since you're comparing the same
thing with itself.
[…]
For testing purposes, I've rebuilt busybox (1:1.20.0-4) with only
shell-ash-export-HOME.patch disabled:
--- busybox-1.20.0/debian/patches/series
+++ busybox-1.20.0/debian/patches/series
@@ -1,6 +1,6 @@
1.20.1.patch
-shell-ash-export-HOME.patch
+#shell-ash-export-HOME.patch
# we need to get rid of this one:
#applets-fallback.patch
version.patch
and the segfaults in busybox awk vanished.
Regards
Stefan Lippers-Hollmann
[1]
http://svn.berlios.de/svnroot/repos/fullstory/fll-live-initramfs/trunk/scripts/fll
signature.asc
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Bug#679377: Segmentation fault when initramfs is booting
Package: busybox Version: 1:1.20.0-4 Severity: important the patch shell-ash-export-HOME.patch causes a segmentation fault when initramfs boots, I believe that this fault occurs the first time that initramfs looks for some executable in the initramfs filesystem, Also, the latest release of busybox, 1.20.1 is a bit different of that, and more upstream stable patches have been added. A new release can be packaged containing this changes, Modifying this, busybox works fine, http://livenet.selfip.com/ftp/debian/package- modifications/busybox_1.20.1-1.lnet1.debian.tar.gz Kind regards, Jordi Pujol Live never ending Tale GNU/Linux Live forever! http://livenet.selfip.com -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/201206281114.23231.jordipuj...@gmail.com
