[Pkg-samba-maint] Bug#483502: smbfs: mount -o remount, brl or -o remount, nobrl changes the reported "mand" option, but has no effect

[Daniel Kahn Gillmor]

Package: smbfs
Version: 1:3.0.28a-3
Severity: normal

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When remounting a CIFS mount to change the byte-range locking option,
the system reports success; but the system's behavior continues to
reflect the originally-mounted choice.

While researching http://bugs.debian.org/483216, i discovered that
byte-range locks against files CIFS shares mounted with mount.cifs are
normally interpreted as "mandatory" locks, instead of "advisory"
locks.  This is adjustable with the nobrl/brl mount options.  mount
claims to be able to successfully modify those options using -o
remount, but in practice, the changed options don't seem to have any
effect at all, and the option selected at initial mount time is the
persistent behavior.

In particular, locking a certain range of a file with a read lock and
then locking the same range with a write lock gives an error when a
CIFS share is mounted with "brl".  This doesn't make much sense to me,
but i'm willing to accept it as intended for now.

I wrote a simple program (source attached) to test this locking
behavior.  I also observed that "brl" is translated into the "mand"
option in the relevant line in /proc/mounts, and that "nobrl" maps to
the *absence* of the "mand" option in the /proc/mounts entry.

You can adjust the options reported in /proc/mounts using the standard
"mount -o remount,newoptions" syntax, but the mountpoint's behavior
does not change. 

Here's a transcript demonstrating the problem.  "bob" is running the
most recent version of samba available in debian etch.  Note that the
behavior of the "testlocking" program is not changed by the -o remount
commands, even though /proc/mounts reflects the change:

[0 root at squeak ~]# grep /mnt /proc/mounts 
[1 root at squeak ~]# mount -t cifs -o guest,uid=dkg,sec=none //bob/dmz /mnt
[0 root at squeak ~]# grep /mnt /proc/mounts 
//bob/dmz /mnt cifs rw,mand,unc=\\bob\dmz,username=,uid=1000,posixpaths,rsize=16384,wsize=57344 0 0
[0 root at squeak ~]# touch /mnt/foo
[0 root at squeak ~]# ~dkg/src/cmrg/test/testlocking/testlocking /mnt/foo
write lock failed
[1 root at squeak ~]# mount -o remount,nobrl,guest,uid=dkg,sec=none /mnt
[0 root at squeak ~]# grep /mnt /proc/mounts 
//bob/dmz /mnt cifs rw,unc=\\bob\dmz,username=,uid=1000,posixpaths,rsize=16384,wsize=57344 0 0
[0 root at squeak ~]# ~dkg/src/cmrg/test/testlocking/testlocking /mnt/foo
write lock failed
[1 root at squeak ~]# umount /mnt
[0 root at squeak ~]# grep /mnt /proc/mounts 
[1 root at squeak ~]# mount -t cifs -o nobrl,guest,uid=dkg,sec=none //bob/dmz /mnt
[0 root at squeak ~]# grep /mnt /proc/mounts 
//bob/dmz /mnt cifs rw,unc=\\bob\dmz,username=,uid=1000,posixpaths,rsize=16384,wsize=57344 0 0
[0 root at squeak ~]# ~dkg/src/cmrg/test/testlocking/testlocking /mnt/foo
[0 root at squeak ~]# mount -o remount,brl,guest,uid=dkg,sec=none /mnt
[0 root at squeak ~]# grep /mnt /proc/mounts 
//bob/dmz /mnt cifs rw,mand,unc=\\bob\dmz,username=,uid=1000,posixpaths,rsize=16384,wsize=57344 0 0
[0 root at squeak ~]# ~dkg/src/cmrg/test/testlocking/testlocking /mnt/foo
[0 root at squeak ~]# 

Thanks for maintaining samba packages in debian!  Let me know if i can
help debug further.

       --dkg

[0] http://cmrg.fifthhorseman.net/browser/trunk/test/testlocking/testlocking.c

- -- System Information:
Debian Release: lenny/sid
  APT prefers testing
  APT policy: (500, 'testing'), (200, 'unstable'), (101, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 2.6.24-1-686 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages smbfs depends on:
ii  libc6                        2.7-10      GNU C Library: Shared libraries
ii  netbase                      4.32        Basic TCP/IP networking system
ii  samba-common                 1:3.0.28a-3 Samba common files used by both th

smbfs recommends no packages.

- -- no debconf information

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