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Re: [PATCH 1/4] xfs: fix _xfs_buf_find oops on blocks beyond the filesys

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/4] xfs: fix _xfs_buf_find oops on blocks beyond the filesystem end
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Tue, 22 Jan 2013 09:31:52 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1358772835-21436-2-git-send-email-david@xxxxxxxxxxxxx>
References: <1358772835-21436-1-git-send-email-david@xxxxxxxxxxxxx> <1358772835-21436-2-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0
On 01/21/2013 07:53 AM, 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>

As we briefly chatted, I ended up playing with the same bug a bit and
came to the same general conclusion (invalid blkno leads to a NULL pag),
just wasn't aware you had a fix in the pipe already...

Reviewed-by: Brian Foster <bfoster@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 56d1614..689d726 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) {
> +             /*
> +              * XXX (dgc): we should really be returning EFSCORRUPTED here,
> +              * but none of the higher level infrastructure supports
> +              * returning a specific error on buffer lookup failures.
> +              */
> +             xfs_alert(btp->bt_mount,
> +                       "%s: Block out of range: block 0x%llx, EOFS 0x%llx ",
> +                       __func__, blkno, eofs);
> +             return NULL;
> +     }
> +
>       /* get tree root */
>       pag = xfs_perag_get(btp->bt_mount,
>                               xfs_daddr_to_agno(btp->bt_mount, blkno));
> 

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