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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