Mount does not honor 'user' option.

DoneSubmitted by Diego Nicola Barbato.
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3 participants
  • Danny Milosavljevic
  • Diego Nicola Barbato
  • Ludovic Courtès
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unassigned
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normal
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Diego Nicola Barbato wrote on 1 Oct 2019 15:41
(address . bug-guix@gnu.org)
87lfu4wpjs.fsf@GlaDOS.home
Hey Guix,

I have added the following to `file-systems' in my operating-system
config:

Toggle snippet (8 lines)
(file-system
(device "127.0.0.1")
(mount-point "/home/diego/inf")
(type "9p")
(options "noextend,trans=tcp,dfltuid=1000,dfltgid=998,port=9001,user,nofail")
(mount? #f))

It works almost as expected except that when I try to mount the file
system as a regular user (which is what the option 'user' is supposed to
allow) I get:

$ LC_ALL=C mount inf
mount: /home/diego/inf: must be superuser to use mount.

The command succeeds if I run it as root.

The following steps reproduce the issue without using a 9p file system:

1. Prepare a file system on a loopback device:

$ dd if=/dev/zero of=foo.img bs=1024 count=524288
$ udisksctl loop-setup --file foo.img
Mapped file foo.img as /dev/loop0.
$ sudo mkfs.ext4 -L foofs /dev/loop0

2. Add the following line to /etc/fstab replacing <name> with something
more appropriate:

LABEL=foofs /home/<name>/foofs ext4 defaults,user

3. Try to mount the filesystem as an unprivileged user (This should work
and does work on e.g. Debian 10):

$ mkdir foofs
$ LC_ALL=C mount foofs
mount: /home/<name>/foofs: must be superuser to use mount.

4. Try it with sudo to confirm that everything else works as expected:

$ sudo mount foofs
$ ls foofs
lost+found/

Regards,

Diego
D
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Danny Milosavljevic wrote on 1 Oct 2019 21:27
(name . Diego Nicola Barbato)(address . dnbarbato@posteo.de)(address . 37569@debbugs.gnu.org)
20191001212726.62b763e1@scratchpost.org
Hmm, how is that solved with other distributions? Is "mount" suid root there?
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Diego Nicola Barbato wrote on 1 Oct 2019 23:43
(name . Danny Milosavljevic)(address . dannym@scratchpost.org)(address . 37569@debbugs.gnu.org)
87h84sw39p.fsf@GlaDOS.home
Hello Danny,

Danny Milosavljevic <dannym@scratchpost.org> writes:

Toggle quote (2 lines)
> Hmm, how is that solved with other distributions? Is "mount" suid root there?

Indeed, in Debian both mount and umount are suid root:

$ stat -c "%a %U:%G %n" /bin/*mount
4755 root:root /bin/fusermount
4755 root:root /bin/mount
4755 root:root /bin/umount

Thanks,

Diego
D
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Diego Nicola Barbato wrote on 4 Oct 2019 08:59
(name . Danny Milosavljevic)(address . dannym@scratchpost.org)(address . 37569@debbugs.gnu.org)
87k19lt2r9.fsf@GlaDOS.home
Diego Nicola Barbato <dnbarbato@posteo.de> writes:

Toggle quote (13 lines)
> Hello Danny,
>
> Danny Milosavljevic <dannym@scratchpost.org> writes:
>
>> Hmm, how is that solved with other distributions? Is "mount" suid root there?
>
> Indeed, in Debian both mount and umount are suid root:
>
> $ stat -c "%a %U:%G %n" /bin/*mount
> 4755 root:root /bin/fusermount
> 4755 root:root /bin/mount
> 4755 root:root /bin/umount

I've tried adding "mount" and "umount" to `setuid-programs' in my
operating-system config:

Toggle snippet (6 lines)
(setuid-programs (cons*
#~(string-append #$util-linux "/bin/mount")
#~(string-append #$util-linux "/bin/umount")
%setuid-programs))

Mounting as an unprivileged user now works as expected (even the fancy
9p stuff). Is there any rationale for not adding "mount" and "umount"
to `%setuid-programs' by default?

Thanks,

Diego
L
L
Ludovic Courtès wrote on 6 Oct 2019 14:46
(name . Diego Nicola Barbato)(address . dnbarbato@posteo.de)
87a7aedotm.fsf@gnu.org
Hi,

Diego Nicola Barbato <dnbarbato@posteo.de> skribis:

Toggle quote (11 lines)
> I've tried adding "mount" and "umount" to `setuid-programs' in my
> operating-system config:
>
> (setuid-programs (cons*
> #~(string-append #$util-linux "/bin/mount")
> #~(string-append #$util-linux "/bin/umount")
> %setuid-programs))
>
> Mounting as an unprivileged user now works as expected (even the fancy
> 9p stuff).

Cool!

Toggle quote (3 lines)
> Is there any rationale for not adding "mount" and "umount" to
> `%setuid-programs' by default?

No, especially since they perform the right checks and error out with
“only root can do that” when needed.

I added them in commit 19944227528502e3619a6d1557bc735224f6fef6.

Thanks!

Ludo’.
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