[PATCH] xfs: prevent 32bit overflow in space reservation

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

If we attempt to preallocate more than 2^32 blocks of space in a
single syscall, the transaction block reservation will overflow
leading to a hangs in the superblock block accounting code. This
is trivially reproduced with xfs_io. Fix the problem by capping the
allocation reservation to the maximum number of blocks a single
xfs_bmapi() call can allocate (2^21 blocks).

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_vnodeops.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 66d585c..91dd9c8 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -2299,15 +2299,21 @@ xfs_alloc_file_space(
 			e = allocatesize_fsb;
 		}
 
+		/*
+		 * we can't allocate more than @nimaps extents at a time,
+		 * so prevent a 32bit overflow on the transaction reserve
+		 * by trying to reserve > 16TB worth of blocks for the
+		 * preallocation.
+		 */
+		resblks = min_t(xfs_fileoff_t, (e - s), (MAXEXTLEN * nimaps));
 		if (unlikely(rt)) {
-			resrtextents = qblocks = (uint)(e - s);
+			resrtextents = qblocks = resblks;
 			resrtextents /= mp->m_sb.sb_rextsize;
 			resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0);
 			quota_flag = XFS_QMOPT_RES_RTBLKS;
 		} else {
 			resrtextents = 0;
-			resblks = qblocks = \
-				XFS_DIOSTRAT_SPACE_RES(mp, (uint)(e - s));
+			resblks = qblocks = XFS_DIOSTRAT_SPACE_RES(mp, resblks);
 			quota_flag = XFS_QMOPT_RES_REGBLKS;
 		}
 
-- 
1.7.1

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