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Re: [PATCH, updated] xfs: Fix possible memory corruption in xfs_readlink

To: Alex Elder <aelder@xxxxxxx>
Subject: Re: [PATCH, updated] xfs: Fix possible memory corruption in xfs_readlink
From: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
Date: Mon, 7 Nov 2011 14:31:08 -0200
Cc: XFS Mailing List <xfs@xxxxxxxxxxx>, Ben Hutchings <ben@xxxxxxxxxxxxxxx>
In-reply-to: <1320682224.3186.5.camel@doink>
References: <1320156842.30281.28.camel@deadeye> <1320682224.3186.5.camel@doink>
User-agent: Mutt/1.5.20 (2009-12-10)
ACK, below my signoff
On Mon, Nov 07, 2011 at 10:10:24AM -0600, Alex Elder wrote:
> From: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
> 
> Fixes a possible memory corruption when the link is larger than
> MAXPATHLEN and XFS_DEBUG is not enabled. This also remove the
> S_ISLNK assert, since the inode mode is checked previously in
> xfs_readlink_by_handle() and via VFS.
> 
> Updated to address concerns raised by Ben Hutchings about the loose
> attention paid to 32- vs 64-bit values, and the lack of handling a
> potentially negative pathlen value:
>  - Changed type of "pathlen" to be xfs_fsize_t, to match that of
>    ip->i_d.di_size
>  - Added checking for a negative pathlen to the too-long pathlen
>    test, and generalized the message that gets reported in that case
>    to reflect the change
> As a result, if a negative pathlen were encountered, this function
> would return EFSCORRUPTED (and would fail an assertion for a debug
> build)--just as would a too-long pathlen.
> 
> Signed-off-by Alex Elder <aelder@xxxxxxx>
Signed-off-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>

> 
> ---
>  fs/xfs/xfs_vnodeops.c |   14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> Index: b/fs/xfs/xfs_vnodeops.c
> ===================================================================
> --- a/fs/xfs/xfs_vnodeops.c
> +++ b/fs/xfs/xfs_vnodeops.c
> @@ -112,7 +112,7 @@ xfs_readlink(
>       char            *link)
>  {
>       xfs_mount_t     *mp = ip->i_mount;
> -     int             pathlen;
> +     xfs_fsize_t     pathlen;
>       int             error = 0;
>  
>       trace_xfs_readlink(ip);
> @@ -122,13 +122,19 @@ xfs_readlink(
>  
>       xfs_ilock(ip, XFS_ILOCK_SHARED);
>  
> -     ASSERT(S_ISLNK(ip->i_d.di_mode));
> -     ASSERT(ip->i_d.di_size <= MAXPATHLEN);
> -
>       pathlen = ip->i_d.di_size;
>       if (!pathlen)
>               goto out;
>  
> +     if (pathlen < 0 || pathlen > MAXPATHLEN) {
> +             xfs_alert(mp, "%s: inode (%llu) bad symlink length (%lld)",
> +                      __func__, (unsigned long long) ip->i_ino,
> +                      (long long) pathlen);
> +             ASSERT(0);
> +             return XFS_ERROR(EFSCORRUPTED);
> +     }
> +
> +
>       if (ip->i_df.if_flags & XFS_IFINLINE) {
>               memcpy(link, ip->i_df.if_u1.if_data, pathlen);
>               link[pathlen] = '\0';
> 
> 
> 
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-- 
--Carlos

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