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Re: [PATCH 5/5] xfs: Correctly lock inode when removing suid and securit

To: Jan Kara <jack@xxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 5/5] xfs: Correctly lock inode when removing suid and security marks
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 14 Apr 2015 11:54:55 -0500
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1425379119-3773-6-git-send-email-jack@xxxxxxx>
References: <1425379119-3773-1-git-send-email-jack@xxxxxxx> <1425379119-3773-6-git-send-email-jack@xxxxxxx>
On 3/3/15 4:38 AM, Jan Kara wrote:
> Currently XFS calls file_remove_privs() without holding i_mutex. This is
> wrong because that function can end up messing with file permissions and
> security xattrs for which we need i_mutex held.
> 
> Fix the problem by grabbing iolock exclusively when we will need to
> change anything in permissions / xattrs.
> 
> Signed-off-by: Jan Kara <jack@xxxxxxx>

This seems like it stands alone, modulo the file_remove_privs function
renaming... should it just be pulled into XFS by Dave?  I guess that would
require the renaming patch to be rebased...

Thanks,
-Eric


> ---
>  fs/xfs/xfs_file.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index fa81a43702ee..3d601e92bd44 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -563,6 +563,13 @@ restart:
>       if (error)
>               return error;
>  
> +     /* For changing security info in file_remove_privs() we need i_mutex */
> +     if (*iolock == XFS_IOLOCK_SHARED && !IS_NOSEC(inode)) {
> +             xfs_rw_iunlock(ip, *iolock);
> +             *iolock = XFS_IOLOCK_EXCL;
> +             xfs_rw_ilock(ip, *iolock);
> +             goto restart;
> +     }
>       /*
>        * If the offset is beyond the size of the file, we need to zero any
>        * blocks that fall between the existing EOF and the start of this
> @@ -601,7 +608,9 @@ restart:
>        * setgid bits if the process is not being run by root.  This keeps
>        * people from modifying setuid and setgid binaries.
>        */
> -     return file_remove_privs(file);
> +     if (!IS_NOSEC(inode))
> +             return file_remove_privs(file);
> +     return 0;
>  }
>  
>  /*
> 

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