Patchwork [4/4,v2] ext4: fix possible use-after-free ext4_remove_li_request()

login
register
mail settings
Submitter Lukas Czerner
Date May 20, 2011, 11:20 a.m.
Message ID <1305890442-16361-4-git-send-email-lczerner@redhat.com>
Download mbox | patch
Permalink /patch/96587/
State Accepted
Headers show

Comments

Lukas Czerner - May 20, 2011, 11:20 a.m.
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>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
---
[v2]: Add reviewed by Eric Sandeen
 fs/ext4/super.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)
Theodore Ts'o - May 20, 2011, 6:22 p.m.
On Fri, May 20, 2011 at 01:20:42AM -0000, Lukas Czerner wrote:
> 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>
> Reviewed-by: Eric Sandeen <sandeen@redhat.com>

I've merged all four lazyinit patches into the ext4 tree, thanks.

     	    	     	      	      	   - Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

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;