[Devel] [PATCH rh7] cbt: fix panic in blk_cbt_map_copy_once()

[Maxim Patlasov]

Avoid panic if userspace erroneously calls ioctl(PLOOP_IOC_PUSH_BACKUP_INIT)
while CBT is off (i.e. q->cbt == NULL).

https://jira.sw.ru/browse/PSBM-47416

Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
---
 block/blk-cbt.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/blk-cbt.c b/block/blk-cbt.c
index 8cdf1d6..8ba52fb 100644
--- a/block/blk-cbt.c
+++ b/block/blk-cbt.c
@@ -290,7 +290,11 @@ int blk_cbt_map_copy_once(struct request_queue *q, __u8 *uuid,
 	mutex_lock(&cbt_mutex);
 	cbt = q->cbt;
 
-	BUG_ON(!cbt);
+	if (!cbt) {
+		mutex_unlock(&cbt_mutex);
+		return -ENOENT;
+	}
+
 	BUG_ON(!cbt->map);
 	BUG_ON(!cbt->block_max);