linux-ext4 - [PATCH 4/4 v2] ext4: fix possible use-after-free ext4_remove_li

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Message-Id: <1305890442-16361-4-git-send-email-lczerner@redhat.com>
Date:	Fri, 20 May 2011 13:20:42 +0200
From:	Lukas Czerner <lczerner@...hat.com>
To:	linux-ext4@...r.kernel.org
Cc:	sandeen@...hat.com, tytso@....edu,
	Lukas Czerner <lczerner@...hat.com>
Subject: [PATCH 4/4 v2] ext4: fix possible use-after-free ext4_remove_li_request()

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@...hat.com>
Reviewed-by: Eric Sandeen <sandeen@...hat.com>
---
[v2]: Add reviewed by Eric Sandeen
 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 72df905..f4d3333 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2720,14 +2720,16 @@ 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;
-
-	if (!ext4_li_info)
+	mutex_lock(&ext4_li_mtx);
+	if (!ext4_li_info) {
+		mutex_unlock(&ext4_li_mtx);
 		return;
+	}
 
 	mutex_lock(&ext4_li_info->li_list_mtx);
-	ext4_remove_li_request(elr);
+	ext4_remove_li_request(EXT4_SB(sb)->s_li_request);
 	mutex_unlock(&ext4_li_info->li_list_mtx);
+	mutex_unlock(&ext4_li_mtx);
 }
 
 static struct task_struct *ext4_lazyinit_task;
-- 
1.7.4.4

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