xfs: don't allow insert-range to shift extents past the maximum offset

Zorro Lang reports that generic/485 blows an assert on a filesystem with
512 byte blocks.  The test tries to fallocate a post-eof extent at the
maximum file size and calls insert range to shift the extents right by
two blocks.  On a 512b block filesystem this causes startoff to overflow
the 54-bit startoff field, leading to the assert.

Therefore, always check the rightmost extent to see if it would overflow
prior to invoking the insert range machinery.

Reported-by: zlang@redhat.com
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=200137
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 7b4a43deb83e..059bc44c27e8 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -1529,6 +1529,8 @@ typedef struct xfs_bmdr_block {
 #define BMBT_STARTBLOCK_BITLEN	52
 #define BMBT_BLOCKCOUNT_BITLEN	21
 
+#define BMBT_STARTOFF_MASK	((1ULL << BMBT_STARTOFF_BITLEN) - 1)
+
 typedef struct xfs_bmbt_rec {
 	__be64			l0, l1;
 } xfs_bmbt_rec_t;