[PATCH 5.1 111/122] dm: make sure to obey max_io_len_target_boundary

[Greg Kroah-Hartman]

From: Michael Lass <bevan@xxxxxxxxx>

commit 51b86f9a8d1c4bb4e3862ee4b4c5f46072f7520d upstream.

Commit 61697a6abd24 ("dm: eliminate 'split_discard_bios' flag from DM
target interface") incorrectly removed code from
__send_changing_extent_only() that is required to impose a per-target IO
boundary on IO that exceeds max_io_len_target_boundary().  Otherwise
"special" IO (e.g. DISCARD, WRITE SAME, WRITE ZEROES) can write beyond
where allowed.

Fix this by restoring the max_io_len_target_boundary() limit in
__send_changing_extent_only()

Fixes: 61697a6abd24 ("dm: eliminate 'split_discard_bios' flag from DM target interface")
Cc: stable@xxxxxxxxxxxxxxx # 5.1+
Signed-off-by: Michael Lass <bevan@xxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1467,7 +1467,7 @@ static unsigned get_num_write_zeroes_bio
 static int __send_changing_extent_only(struct clone_info *ci, struct dm_target *ti,
 				       unsigned num_bios)
 {
-	unsigned len = ci->sector_count;
+	unsigned len;
 
 	/*
 	 * Even though the device advertised support for this type of
@@ -1478,6 +1478,8 @@ static int __send_changing_extent_only(s
 	if (!num_bios)
 		return -EOPNOTSUPP;
 
+	len = min((sector_t)ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
+
 	__send_duplicate_bios(ci, ti, num_bios, &len);
 
 	ci->sector += len;