xfs: prevent 32bit overflow in space reservation

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 66d585c6917c..4c7c7bfb2b2f 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -2299,15 +2299,22 @@ xfs_alloc_file_space(
                         e = allocatesize_fsb;
                 }
 
+                /*
+                 * The transaction reservation is limited to a 32-bit block
+                 * count, hence we need to limit the number of blocks we are
+                 * trying to reserve to avoid an overflow. We can't allocate
+                 * more than @nimaps extents, and an extent is limited on disk
+                 * to MAXEXTLEN (21 bits), so use that to enforce the limit.
+                 */
+                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;
                 }