linux-kernel - [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check

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Message-Id: <20190729032401.28081-1-baijiaju1990@gmail.com>
Date:   Mon, 29 Jul 2019 11:24:01 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     darrick.wong@...cle.com, bfoster@...hat.com, sandeen@...deen.net
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] fs: 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@...il.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);
 out:
 	return error;
 }
-- 
2.17.0