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SubjectRe: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()
On Mon, Jul 29, 2019 at 11:24:01AM +0800, Jia-Ju Bai wrote:
> In xchk_da_btree_block_check_sibling(), there is an if statement on
> line 274 to check whether ds->state->altpath.blk[level].bp is NULL:
> if (ds->state->altpath.blk[level].bp)
>
> When ds->state->altpath.blk[level].bp is NULL, it is used on line 281:
> xfs_trans_brelse(..., ds->state->altpath.blk[level].bp);
> struct xfs_buf_log_item *bip = bp->b_log_item;
> ASSERT(bp->b_transp == tp);
>
> Thus, possible null-pointer dereferences may occur.
>
> To fix these bugs, ds->state->altpath.blk[level].bp is checked before
> being used.
>
> These bugs are found by a static analysis tool STCheck written by us.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
> fs/xfs/scrub/dabtree.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
> index 94c4f1de1922..33ff90c0dd70 100644
> --- a/fs/xfs/scrub/dabtree.c
> +++ b/fs/xfs/scrub/dabtree.c
> @@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling(
> /* Compare upper level pointer to sibling pointer. */
> if (ds->state->altpath.blk[level].blkno != sibling)
> xchk_da_set_corrupt(ds, level);
> - xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp);
> + if (ds->state->altpath.blk[level].bp)
> + xfs_trans_brelse(ds->dargs.trans,
> + ds->state->altpath.blk[level].bp);

Indentation here (in xfs we use two spaces)

Also, uh, shouldn't we set ds->state->altpath.blk[level].bp to NULL
since we've released the buffer?

--D

> out:
> return error;
> }
> --
> 2.17.0
>

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