[linux-cifs-client] [PATCH] cifs: guard against hardlinking directories

[Suresh Jayaraman]

On 05/07/2010 08:38 PM, Suresh Jayaraman wrote:
> On 05/07/2010 07:33 PM, Jeff Layton wrote:
>> When we made serverino the default, we trusted that the field sent by the
>> server in the "uniqueid" field was actually unique. It turns out that it
>> isn't reliably so.
>>
>> Samba, in particular, will just put the st_ino in the uniqueid field when
>> unix extensions are enabled. When a share spans multiple filesystems, it's
>> quite possible that there will be collisions. This is a server bug, but
>> when the inodes in question are a directory (as is often the case) and
>> there is a collision with the root inode of the mount, the result is a
>> kernel panic on umount.
>>
>> Fix this by checking explicitly for directory inodes with the same
>> uniqueid. If that is the case, then we can assume that using server inode
>> numbers will be a problem and that they should be disabled.
>>
>> Signed-off-by: Jeff Layton <jlayton at redhat.com>
>> ---
>>  fs/cifs/cifsglob.h |    1 +
>>  fs/cifs/inode.c    |   21 +++++++++++++++++++--
>>  2 files changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
>> index ecf0ffb..0c2fd17 100644
>> --- a/fs/cifs/cifsglob.h
>> +++ b/fs/cifs/cifsglob.h
>> @@ -502,6 +502,7 @@ struct dfs_info3_param {
>>  #define CIFS_FATTR_DFS_REFERRAL		0x1
>>  #define CIFS_FATTR_DELETE_PENDING	0x2
>>  #define CIFS_FATTR_NEED_REVAL		0x4
>> +#define CIFS_FATTR_INO_COLLISION	0x8
>>  
> 
> Nice and thoughful solution! I was not for disabling serverino as a default.
> 
> I have a nice way of reliably reproducing the problem.
> 
> - create two small partitions and format (ext3)
> - mount first partition as /vol1 and mount the second as /vol1/vol2
>   inside the first
> - create files on both partitions (say 10 files)
> - export them
> - mount from the client, access them
> - the inode numbers will easily collide
> - umount them and the client will crash..
> 
> I'm trying out the fix and will be able to verify (hopefully before I
> catch my train in another couple of hours). Will revert back after testing.
> 

Voila! The patch fixes the panic (and serverino autodisabled if a
duplicate inode number is found -- from dmesg) when testing using the
above mentioned test case.

Reviewed-and-Tested-by: Suresh Jayaraman <sjayaraman at suse.de>


Thanks,

-- 
Suresh Jayaraman