[PATCH v2] xfs: check for possible overflow in xfs_ioc_trim

[Tomas Racek <tracek@redhat.com>]

If range.start points behind the filesystem, return invalid value error.
This fixes possible overflow in

start = BTOBB(range.start)

when range.start is nearly ULLONG_MAX.

Signed-off-by: Tomas Racek <tracek@redhat.com>
---
 fs/xfs/xfs_discard.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
index f9c3fe3..33d367f 100644
--- a/fs/xfs/xfs_discard.c
+++ b/fs/xfs/xfs_discard.c
@@ -179,12 +179,13 @@ xfs_ioc_trim(
 	 * used by the fstrim application.  In the end it really doesn't
 	 * matter as trimming blocks is an advisory interface.
 	 */
+	if (range.start >= XFS_FSB_TO_B(mp, mp->m_sb.sb_dblocks))
+		return -XFS_ERROR(EINVAL);
+
 	start = BTOBB(range.start);
 	end = start + BTOBBT(range.len) - 1;
 	minlen = BTOBB(max_t(u64, granularity, range.minlen));
 
-	if (XFS_BB_TO_FSB(mp, start) >= mp->m_sb.sb_dblocks)
-		return -XFS_ERROR(EINVAL);
 	if (end > XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks) - 1)
 		end = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks)- 1;
 
-- 
1.7.7.6