Re: chpst -u and supplementary groups
Laurent Bercot schrob: > I don't think the historical behaviour is a *bug*, because the > historical behaviour is documented and conforms to its documentation. Well, let's say "misfeature" ;) > It also comes from a time when supplementary groups weren't used as > much as they are today. > > It's just that not having supplementary groups can defeat intuitive > expectations when performing a group permissions check. That does not > happen every day, but it does happen sometimes. s6-setuidgid had the > same behaviour as setuidgid until I got bitten by that very problem, > at which point I realized that "user identity" is not only uid and gid > as it is for files, but also supplementary groups, and so I added > supplementary groups support to s6-*uidgid. But it had been years > until I found it necessary. Ok, that's the kind of answer I was hoping for, thanks. > So, YMMV. I'd say supplementary groups support is useful and allows > the tool to better match user intuition, so it has value. But is it > *mandatory* for correctness? You decide. I don't need to decide that. :) I already knew that *I* needed supplementary group support. The only question was whether I should implement it in runit's source code, or by piping the output of getent through sed, and writing "chpst -u `userid acc` prog..." in my runscripts as a matter of habit. And now the former sounds like the more reasonable course of action. I'll go have a look at the code... cheers, Jan signature.asc Description: PGP signature
Re: chpst -u and supplementary groups
Cameron Nemo schrob: > Most of these (su, sudo, runuser) go through PAM. > su and sudo are primarily targeted at interactive use. As a shell junkie, I don't subscribe to the viewpoint that there's a measurable difference between "interactive use" and "scripting". ;) > > So now I'm wondering: > > What are the use cases for not applying existing supplementary groups? > It requires additional fact finding by what amounts to a shim between > the OS and the service. That's not a use case, that's just the KISS ssoftware design principle. But are there actually reasons for wanting to *avoid* a user's supplementary groups, implementation issues aside? > Use cases are questionable -- why is a login session not more suitable? I'm sorry, I don't understand. What's a login session? > Yeah let's not do this. A good implementation is possible, and has been done. > > [...] > > Nobody maintains runit, so who is taking this patch? Dmitry Bogatov has been quite active in runit integration for Debian during the last year or so. This is what vexes me about the daemontools family. Apparently it's so easy to reimplement them that people keep doing that. Instead of working together to get one implementation polished enough to make a big unix distro use it by default. cheers, Jan signature.asc Description: PGP signature
Re: chpst -u and supplementary groups
On Mon, Aug 19, 2019 at 5:08 AM Jan Braun wrote: > > Hello list! > > Yesterday, I spent way too much time chasing down a permissions problem > caused by the fact that "chpst -u acc prog..." only sets the account's > primary group, and ignores any supplementary groups the account may be a > member of. > > TFM mentions "All initial supplementary groups are removed.", but I > failed to memorize that. (Also, what does "initial" signify here?) > > My inability to see the issue came from the fact that all other similar > programs (I'm aware of) do in fact add the supplementary groups. Watch: > > | # chpst -u test id > | uid=1003(test) gid=1003(test) groups=1003(test) > | # runuser -u test id > | uid=1003(test) gid=1003(test) groups=1003(test),4(adm) > | # s6-setuidgid test id > | uid=1003(test) gid=1003(test) groups=1003(test),4(adm) > | # su - test -c id > | uid=1003(test) gid=1003(test) groups=1003(test),4(adm) > | # su test -c id > | uid=1003(test) gid=1003(test) groups=1003(test),4(adm) > | # sudo -u test id > | uid=1003(test) gid=1003(test) groups=1003(test),4(adm) > | # Most of these (su, sudo, runuser) go through PAM. su and sudo are primarily targeted at interactive use. I found another outlier, Google's minijail0: / # chpst -u cameronnemo /usr/bin/id uid=1000(cameronnemo) gid=1000(cameronnemo) grupos=1000(cameronnemo) / # minijail0 -u cameronnemo /usr/bin/id uid=1000(cameronnemo) gid=0(root) grupos=0(root) / # minijail0 -u cameronnemo -g cameronnemo /usr/bin/id uid=1000(cameronnemo) gid=1000(cameronnemo) grupos=1000(cameronnemo) > > So now I'm wondering: > What are the use cases for not applying existing supplementary groups? It requires additional fact finding by what amounts to a shim between the OS and the service. Use cases are questionable -- why is a login session not more suitable? Workarounds and other options exist, as demonstrated above. > Should chpst apply them by default? I would rather it not. > Should chpst grow an option to (not) apply them? Depends on the implementation. > "chpst -u acc: prog..." is still free. > Or is everything as it's supposed to be, and people might need to munge > the output of "getent initgroups acc" and feed it to the -u option? Yeah let's not do this. A good implementation is possible, and has been done. > I'll be happy to try to come up with a patch (even if it's still a > fatter warning in the manpage) if people can agree here what the right > thing to do is. Nobody maintains runit, so who is taking this patch? > regards, > Jan Cheers, Cameron
Re: chpst -u and supplementary groups
Yes. Apparently everyone re-implementing daemontools does something like this. So that brings me back to my original question: is there consensus that the historical behaviour is a bug? Or are there valid use cases¹? I don't think the historical behaviour is a *bug*, because the historical behaviour is documented and conforms to its documentation. It also comes from a time when supplementary groups weren't used as much as they are today. It's just that not having supplementary groups can defeat intuitive expectations when performing a group permissions check. That does not happen every day, but it does happen sometimes. s6-setuidgid had the same behaviour as setuidgid until I got bitten by that very problem, at which point I realized that "user identity" is not only uid and gid as it is for files, but also supplementary groups, and so I added supplementary groups support to s6-*uidgid. But it had been years until I found it necessary. So, YMMV. I'd say supplementary groups support is useful and allows the tool to better match user intuition, so it has value. But is it *mandatory* for correctness? You decide. -- Laurent
Re: chpst -u and supplementary groups
Jonathan de Boyne Pollard schrob: > > My inability to see the issue came from the fact that all other similar > > programs (I'm aware of) do in fact add the supplementary groups. > > > Then you are not aware of Bernstein daemontools, where setuidgid does not. > (-: Well, I am aware of their existance, but I've never used them, only various descendants. I even suspected they might not handle supplementary groups, because e.g. s6-envuidgid introduces GIDLIST to deal with them. > Setting only one group was the behaviour of the original tool. Setting the > supplementary groups as well is behaviour that others added to their > toolsets later. Bruce Guenter (in daemontools-encore) and I added it as an > optional behaviour for setuidgid. Yes. Apparently everyone re-implementing daemontools does something like this. So that brings me back to my original question: is there consensus that the historical behaviour is a bug? Or are there valid use cases¹? cheers, Jan ¹) Besides when the account has no supplementary groups, obviously. signature.asc Description: PGP signature
Re: chpst -u and supplementary groups
My inability to see the issue came from the fact that all other similar programs (I'm aware of) do in fact add the supplementary groups. Then you are not aware of Bernstein daemontools, where setuidgid does not. (-: # /package/admin/djbwares/command/setuidgid operator id uid=2(operator) gid=5(operator) groups=5(operator) # * http://jdebp.uk./Softwares/djbwares/guide/commands/setuidgid.xml Setting only one group was the behaviour of the original tool. Setting the supplementary groups as well is behaviour that others added to their toolsets later. Bruce Guenter (in daemontools-encore) and I added it as an optional behaviour for setuidgid. # /package/admin/nosh/command/setuidgid operator id uid=2(operator) gid=5(operator) groups=5(operator) # /package/admin/nosh/command/setuidgid --supplementary operator id uid=2(operator) gid=5(operator) groups=5(operator),1298(log) # * http://jdebp.uk./Softwares/nosh/guide/commands/setuidgid.xml * http://untroubled.org/daemontools-encore/setuidgid.8.html
