[PATCH v5 6/9] xfs: clamp the pNFS layout range to the maximum file size

[Daejun Park via B4 Relay <devnull+daejun7.park.samsung.com@kernel.org>]

From: Daejun Park <daejun7.park@samsung.com>

xfs_fs_map_blocks() lets two bad layout ranges through. An offset of
2^63 or more is negative and passes "offset > limit". A length above
the limit, such as NFS4_UINT64_MAX, wraps "offset > limit - length"
and stays unclamped. With NFS4_UINT64_MAX, a read layout is built from
an uninitialized mapping.

Reject a negative offset and one at the limit, and clamp the length.
This needs "xfs: cap the block count of xfs_iomap_write_direct() at one
extent".

Fixes: 527851124d10 ("xfs: implement pNFS export operations")
Cc: stable@vger.kernel.org
Signed-off-by: Daejun Park <daejun7.park@samsung.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
Tested with pynfs: a READ LAYOUTGET for NFS4_UINT64_MAX bytes at
offset 0 and one for 4 KiB at 2^63 got NFS4ERR_IO before, and get
NFS4ERR_INVAL after. The first fails when nfsd asks again at 2^63,
after the last extent.
---
 fs/xfs/xfs_pnfs.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
index 19eb18e129..7153e7a1e1 100644
--- a/fs/xfs/xfs_pnfs.c
+++ b/fs/xfs/xfs_pnfs.c
@@ -176,10 +176,9 @@ xfs_fs_map_blocks(
 	if (!write)
 		limit = max(limit, round_up(i_size_read(inode),
 				     inode->i_sb->s_blocksize));
-	if (offset > limit)
+	if (offset < 0 || offset >= limit)
 		goto out_unlock;
-	if (offset > limit - length)
-		length = limit - offset;
+	length = min_t(u64, length, limit - offset);
 
 	error = filemap_write_and_wait(inode->i_mapping);
 	if (error)

-- 
2.43.0