From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: xfs <linux-xfs@vger.kernel.org>
Subject: [PATCH] xfs: fix sign handling problem in xfs_bmbt_diff_two_keys
Date: Mon, 26 Aug 2019 11:38:03 -0700 [thread overview]
Message-ID: <20190826183803.GQ1037350@magnolia> (raw)
From: Darrick J. Wong <darrick.wong@oracle.com>
In xfs_bmbt_diff_two_keys, we perform a signed int64_t subtraction with
two unsigned 64-bit quantities. If the second quantity is actually the
"maximum" key (all ones) as used in _query_all, the subtraction
effectively becomes addition of two positive numbers and the function
returns incorrect results. Fix this with explicit comparisons of the
unsigned values.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/libxfs/xfs_bmap_btree.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
index fbb18ba5d905..3c1a805b3775 100644
--- a/fs/xfs/libxfs/xfs_bmap_btree.c
+++ b/fs/xfs/libxfs/xfs_bmap_btree.c
@@ -400,8 +400,20 @@ xfs_bmbt_diff_two_keys(
union xfs_btree_key *k1,
union xfs_btree_key *k2)
{
- return (int64_t)be64_to_cpu(k1->bmbt.br_startoff) -
- be64_to_cpu(k2->bmbt.br_startoff);
+ uint64_t a = be64_to_cpu(k1->bmbt.br_startoff);
+ uint64_t b = be64_to_cpu(k2->bmbt.br_startoff);
+
+ /*
+ * Note: This routine previously casted a and b to int64 and subtracted
+ * them to generate a result. This lead to problems if b was the
+ * "maximum" key value (all ones) being signed incorrectly, hence this
+ * somewhat less efficient version.
+ */
+ if (a > b)
+ return 1;
+ else if (b > a)
+ return -1;
+ return 0;
}
static xfs_failaddr_t
next reply other threads:[~2019-08-26 18:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 18:38 Darrick J. Wong [this message]
2019-08-29 7:23 ` [PATCH] xfs: fix sign handling problem in xfs_bmbt_diff_two_keys Christoph Hellwig
2019-08-29 15:41 ` Darrick J. Wong
2019-08-30 15:30 ` Christoph Hellwig
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