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Re: [PATCH] xfs: fix _xfs_buf_find oops on blocks beyond the filesystem

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix _xfs_buf_find oops on blocks beyond the filesystem end
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 3 Jan 2013 15:22:22 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1355870625-26638-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1355870625-26638-1-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Dave,

On Wed, Dec 19, 2012 at 09:43:45AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> When _xfs_buf_find is passed an out of range address, it will fail
> to find a relevant struct xfs_perag and oops with a null
> dereference. This can happen when trying to walk a filesystem with a
> metadata inode that has a partially corrupted extent map (i.e. the
> block number returned is corrupt, but is otherwise intact) and we
> try to read from the corrupted block address.
> 
> In this case, just fail the lookup. If it is readahead being issued,
> it will simply not be done, but if it is real read that fails we
> will get an error being reported.  Ideally this case should result
> in an EFSCORRUPTED error being reported, but we cannot return an
> error through xfs_buf_read() or xfs_buf_get() so this lookup failure
> may result in ENOMEM or EIO errors being reported instead.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_buf.c |   18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index a80195b..16249d9 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -487,6 +487,7 @@ _xfs_buf_find(
>       struct rb_node          *parent;
>       xfs_buf_t               *bp;
>       xfs_daddr_t             blkno = map[0].bm_bn;
> +     xfs_daddr_t             eofs;
>       int                     numblks = 0;
>       int                     i;
>  
> @@ -498,6 +499,23 @@ _xfs_buf_find(
>       ASSERT(!(numbytes < (1 << btp->bt_sshift)));
>       ASSERT(!(BBTOB(blkno) & (xfs_off_t)btp->bt_smask));
>  
> +     /*
> +      * Corrupted block numbers can get through to here, unfortunately, so we
> +      * have to check that the buffer falls within the filesystem bounds.
> +      */
> +     eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
> +     if (blkno >= eofs || blkno + numblks > eofs) {
                             ^^^^^^^^^^^^^^^^^^^^^^

That looks suspect to me.  I think you need to go over each buffer
individually.

I bounced it off Mark and this was his suggestion:

 for (i = 0; i < nmaps; i++) {
         if (map[i].bm_bn >= eofs ||
                     map[i].bm_bn + map[i].bm_len >= eofs)
                         ...

Regards,
        Ben

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