[PATCH 1/1] xfs: fix overlapping extents returned for pNFS LAYOUTGET

[Dai Ngo <dai.ngo@oracle.com>]

xfs_fs_map_blocks() currently passes XFS_BMAPI_ENTIRE to xfs_bmapi_read(),
which causes the bmap code to expand the mapping to cover the entire
extent rather than the requested range.

A single LAYOUTGET request from the client can cause the server to
issue multiple calls to xfs_fs_map_blocks() for different offsets
within the same extent. Because the use of XFS_BMAPI_ENTIRE flag,
these calls can produce overlapping mappings.

As a result, the LAYOUTGET reply sent to the NFS client may contain
overlapping extents. This creates ambiguity in extent selection for a
given file range, which can lead to incorrect device selection,
inconsistent handling of datastate, and ultimately data corruption or
protocol violations on the client side.

Problem discovered with xfstest generic/075 test using NFSv4.2 mount
with SCSI layout.

Fix this by replacing the XFS_BMAPI_ENTIRE flag with '0' so that
xfs_bmapi_read() returns only the mapping for the requested range.

Also drop the check for (!error) since it was checked after call to
xfs_bmapi_read().

Fixes: cc6c40e09d7b1 ("NFSD/blocklayout: Support multiple extents per LAYOUTGET").
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/xfs/xfs_pnfs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

- This patch is based on top of the patch:
  xfs: fix use of uninitialized imap in xfs_fs_map_blocks error path

diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
index f7c6dba3d21e..697bf3e4ad7e 100644
--- a/fs/xfs/xfs_pnfs.c
+++ b/fs/xfs/xfs_pnfs.c
@@ -118,7 +118,7 @@ xfs_fs_map_blocks(
 	struct xfs_bmbt_irec	imap;
 	xfs_fileoff_t		offset_fsb, end_fsb;
 	loff_t			limit;
-	int			bmapi_flags = XFS_BMAPI_ENTIRE;
+	int			bmapi_flags;
 	int			nimaps = 1;
 	uint			lock_flags;
 	int			error = 0;
@@ -172,6 +172,7 @@ xfs_fs_map_blocks(
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);
 
 	lock_flags = xfs_ilock_data_map_shared(ip);
+	bmapi_flags = 0;	/* return map for requested range only */
 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
 				&imap, &nimaps, bmapi_flags);
 	if (error) {
@@ -182,8 +183,7 @@ xfs_fs_map_blocks(
 
 	ASSERT(!nimaps || imap.br_startblock != DELAYSTARTBLOCK);
 
-	if (!error && write &&
-	    (!nimaps || imap.br_startblock == HOLESTARTBLOCK)) {
+	if (write && (!nimaps || imap.br_startblock == HOLESTARTBLOCK)) {
 		if (offset + length > XFS_ISIZE(ip))
 			end_fsb = xfs_iomap_eof_align_last_fsb(ip, end_fsb);
 		else if (nimaps && imap.br_startblock == HOLESTARTBLOCK)
-- 
2.47.3