[PATCH v2] xfs: do not unshare any blocks beyond eof

[Julian Sun <sunjunchao2870@gmail.com>]

Attempting to unshare extents beyond EOF will trigger
the need zeroing case, which in turn triggers a warning.
Therefore, let's skip the unshare process if blocks are
beyond EOF.

This patch passed the xfstests using './check -g quick', without
causing any additional failure

Reported-and-tested-by: syzbot+296b1c84b9cbf306e5a0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=296b1c84b9cbf306e5a0
Fixes: 32a38a499104 ("iomap: use write_begin to read pages to unshare")
Inspired-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Julian Sun <sunjunchao2870@gmail.com>
---
 fs/xfs/xfs_iomap.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 72c981e3dc92..81a0514b8652 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -976,6 +976,7 @@ xfs_buffered_write_iomap_begin(
 	int			error = 0;
 	unsigned int		lockmode = XFS_ILOCK_EXCL;
 	u64			seq;
+	xfs_fileoff_t eof_fsb;
 
 	if (xfs_is_shutdown(mp))
 		return -EIO;
@@ -1016,6 +1017,13 @@ xfs_buffered_write_iomap_begin(
 	if (eof)
 		imap.br_startoff = end_fsb; /* fake hole until the end */
 
+	/* Don't try to unshare any blocks beyond EOF. */
+	eof_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
+	if (flags & IOMAP_UNSHARE && end_fsb > eof_fsb) {
+		xfs_trim_extent(&imap, offset_fsb, eof_fsb - offset_fsb);
+		end_fsb = eof_fsb;
+	}
+
 	/* We never need to allocate blocks for zeroing or unsharing a hole. */
 	if ((flags & (IOMAP_UNSHARE | IOMAP_ZERO)) &&
 	    imap.br_startoff > offset_fsb) {
@@ -1030,7 +1038,6 @@ xfs_buffered_write_iomap_begin(
 	 */
 	if ((flags & IOMAP_ZERO) && imap.br_startoff <= offset_fsb &&
 	    isnullstartblock(imap.br_startblock)) {
-		xfs_fileoff_t eof_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
 
 		if (offset_fsb >= eof_fsb)
 			goto convert_delay;
-- 
2.39.2