[PATCH AUTOSEL 4.14 02/22] null_blk: Handle null_add_dev() failures properly

[Sasha Levin <sashal@kernel.org>]

From: Bart Van Assche <bvanassche@acm.org>

[ Upstream commit 9b03b713082a31a5b90e0a893c72aa620e255c26 ]

If null_add_dev() fails then null_del_dev() is called with a NULL argument.
Make null_del_dev() handle this scenario correctly. This patch fixes the
following KASAN complaint:

null-ptr-deref in null_del_dev+0x28/0x280 [null_blk]
Read of size 8 at addr 0000000000000000 by task find/1062

Call Trace:
 dump_stack+0xa5/0xe6
 __kasan_report.cold+0x65/0x99
 kasan_report+0x16/0x20
 __asan_load8+0x58/0x90
 null_del_dev+0x28/0x280 [null_blk]
 nullb_group_drop_item+0x7e/0xa0 [null_blk]
 client_drop_item+0x53/0x80 [configfs]
 configfs_rmdir+0x395/0x4e0 [configfs]
 vfs_rmdir+0xb6/0x220
 do_rmdir+0x238/0x2c0
 __x64_sys_unlinkat+0x75/0x90
 do_syscall_64+0x6f/0x2f0
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Johannes Thumshirn <jth@kernel.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/block/null_blk.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index e9776ca0996b0..b4078901dbcb9 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -1593,7 +1593,12 @@ static void null_nvm_unregister(struct nullb *nullb) {}
 
 static void null_del_dev(struct nullb *nullb)
 {
-	struct nullb_device *dev = nullb->dev;
+	struct nullb_device *dev;
+
+	if (!nullb)
+		return;
+
+	dev = nullb->dev;
 
 	ida_simple_remove(&nullb_indexes, nullb->index);
 
-- 
2.20.1