[PATCH 7.2 02/10] dm-integrity: fix NULL pointer dereference when the R flag is used

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@redhat.com>

[ Upstream commit 7d4d4f3b668d708d94f62ecdd33ac330a6fd8a84 ]

If the dm-integrity device has the SB_FLAG_DIRTY_BITMAP flag set and the
user activates the device in the 'R' mode, a crash in dm_integrity_resume
happens because the function attempts to read the journal containing the
bitmap.

This patch makes dm-integrity skip any writes to the device in
dm_integrity_resume if the device is activated in the 'R' mode.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 468dfca38b1a ("dm integrity: add a bitmap mode")
Cc: stable@vger.kernel.org
Stable-dep-of: fc79aeb86a2c ("dm-integrity: validate the superblock on resume")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-integrity.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index 4bda7b5dba1a6..cded0607b39c0 100644
--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -3874,6 +3874,10 @@ static void dm_integrity_resume(struct dm_target *ti)
 	r = sync_rw_sb(ic, REQ_OP_READ);
 	if (r)
 		dm_integrity_io_error(ic, "reading superblock", r);
+
+	if (ic->mode == 'R')
+		goto skip_writes;
+
 	if ((ic->sb->flags & flags) != flags) {
 		ic->sb->flags |= flags;
 		r = sync_rw_sb(ic, REQ_OP_WRITE | REQ_FUA);
@@ -3983,6 +3987,7 @@ static void dm_integrity_resume(struct dm_target *ti)
 		}
 	}
 
+skip_writes:
 	ic->reboot_notifier.notifier_call = dm_integrity_reboot;
 	ic->reboot_notifier.next = NULL;
 	ic->reboot_notifier.priority = INT_MAX - 1;	/* be notified after md and before hardware drivers */
-- 
2.53.0