xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()

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>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
index 94c4f1de1922f31ea5f9ffe395792fe3a918c531..77ff9f97bcda53747c0d79e4f82e9337d475fc2d 100644 (file)
--- a/fs/xfs/scrub/dabtree.c
+++ b/fs/xfs/scrub/dabtree.c
@@ -278,7 +278,11 @@ 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);
+               ds->state->altpath.blk[level].bp = NULL;
+       }
 out:
        return error;
 }