Re: [PATCH] Inconsistent setattr behaviour

["Sachin S. Prabhu" <sprabhu@redhat.com>]

Trond Myklebust wrote:
> On Mon, 2009-02-23 at 16:22 +0000, Sachin S. Prabhu wrote:
>> There is an inconsistency seen in the behaviour of nfs compared to other local
>> filesystems on linux when changing owner or group of a directory. If the
>> directory has SUID/SGID flags set, on changing owner or group on the directory,
>> the flags are stripped off on nfs. These flags are maintained on other
>> filesystems such as ext3.
>>
>> To reproduce on a nfs share or local filesystem, run the following commands
>> mkdir test; chmod +s+g test; chown user1 test; ls -ld test
>>
>> On the nfs share, the flags are stripped and the output seen is
>> drwxr-xr-x 2 user1 root 4096 Feb 23  2009 test
>>
>> On other local filesystems(ex: ext3), the flags are not stripped and the output
>> seen is
>> drwsr-sr-x 2 user1 root 4096 Feb 23 13:57 test
>>
>> chown_common() called from sys_chown() will only strip the flags if the inode is
>> not a directory.
>> static int chown_common(struct dentry * dentry, uid_t user, gid_t group)
>> {
>> ..
>>         if (!S_ISDIR(inode->i_mode))
>>                 newattrs.ia_valid |=
>>                         ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
>> ..
>> }
>>
>> See: http://www.opengroup.org/onlinepubs/7990989775/xsh/chown.html
>>
>> "If the path argument refers to a regular file, the set-user-ID (S_ISUID) and
>> set-group-ID (S_ISGID) bits of the file mode are cleared upon successful return
>> from chown(), unless the call is made by a process with appropriate privileges,
>> in which case it is implementation-dependent whether these bits are altered. If
>> chown() is successfully invoked on a file that is not a regular file, these
>> bits may be cleared. These bits are defined in <sys/stat.h>."
>>
>> The behaviour as it stands does not appear to violate POSIX.  However the
>> actions performed are inconsistent when comparing ext3 and nfs.
> 
> Does this patch retain the behaviour that we strip suid/sgid bits on
> executable files?
> 
> IOW: Is the following property retained
> 
> root@heimdal:~# touch /tmp/gnurr; chmod a+x,+s+g /tmp/gnurr; chown
> bin /tmp/gnurr
> root@heimdal:~# ls -l /tmp/gnurr
> -rwxr-xr-x 1 bin root 0 2009-02-23 08:49 /tmp/gnurr
> 
Yes it does

[root@vm22 mnt]# touch t2; chmod a+x,+s+g t2; chown bin t2
[root@vm22 mnt]# ls -l t2
-rwxr-xr-x 1 bin root 0 Feb 23 16:56 t2

The behaviour changes only for directories.
[root@vm22 mnt]# mkdir t3; chmod a+x,+s+g t3; chown bin t3
[root@vm22 mnt]# ls -ld t3
drwsr-sr-x 2 bin root 4096 Feb 23 16:57 t3

Sachin Prabhu