[PATCH 4/4] ext4: fix possible use-after-free ext4_remove_li_request()

[Lukas Czerner <lczerner@redhat.com>]

We need to take reference to the s_li_request after we take a mutex,
because it might be freed since then, hence result in accessing old
already freed memory. Also we should protect the whole
ext4_remove_li_request() because ext4_li_info might be in the process of
being freed in ext4_lazyinit_thread().

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
---
 fs/ext4/super.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c379af6..6a8e48f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2721,14 +2721,16 @@ static void ext4_remove_li_request(struct ext4_li_request *elr)
 
 static void ext4_unregister_li_request(struct super_block *sb)
 {
-	struct ext4_li_request *elr = EXT4_SB(sb)->s_li_request;