[PATCH] ext4: Fix a double free in ext4_register_li_request.

[PATCH] ext4: Fix a double free in ext4_register_li_request.

[Tao Ma]

From: Tao Ma <boyu.mt@taobao.com>

In ext4_register_li_request, we malloc a ext4_li_request and
inserts it into ext4_li_info->li_request_list. In case of any
error later, we free it in the end. But if we have some error
in ext4_run_lazyinit_thread, the whole li_request_list will be
dropped and freed in it. So we will double free this ext4_li_request.

This patch just sets elr to NULL after it is inserted to the list
so that the latter kfree won't double free it.

Cc: stable@kernel.org
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
---
 fs/ext4/super.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 22546ad..2d1378f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2975,6 +2975,12 @@ static int ext4_register_li_request(struct super_block *sb,
 	mutex_unlock(&ext4_li_info->li_list_mtx);
 
 	sbi->s_li_request = elr;
+	/*
+	 * set elr to NULL here since it has been inserted to
+	 * the request_list and the removal and free of it is
+	 * handled by ext4_clear_request_list from now on.
+	 */
+	elr = NULL;
 
 	if (!(ext4_li_info->li_state & EXT4_LAZYINIT_RUNNING)) {
 		ret = ext4_run_lazyinit_thread();
-- 
1.7.4

Re: [PATCH] ext4: Fix a double free in ext4_register_li_request.

[Lukas Czerner]

On Mon, 28 Mar 2011, Tao Ma wrote:

> From: Tao Ma <boyu.mt@taobao.com>
> 
> In ext4_register_li_request, we malloc a ext4_li_request and
> inserts it into ext4_li_info->li_request_list. In case of any
> error later, we free it in the end. But if we have some error
> in ext4_run_lazyinit_thread, the whole li_request_list will be
> dropped and freed in it. So we will double free this ext4_li_request.
> 
> This patch just sets elr to NULL after it is inserted to the list
> so that the latter kfree won't double free it.
> 
> Cc: stable@kernel.org
> Signed-off-by: Tao Ma <boyu.mt@taobao.com>
> ---
>  fs/ext4/super.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 22546ad..2d1378f 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2975,6 +2975,12 @@ static int ext4_register_li_request(struct super_block *sb,
>  	mutex_unlock(&ext4_li_info->li_list_mtx);
>  
>  	sbi->s_li_request = elr;
> +	/*
> +	 * set elr to NULL here since it has been inserted to
> +	 * the request_list and the removal and free of it is
> +	 * handled by ext4_clear_request_list from now on.
> +	 */
> +	elr = NULL;
>  
>  	if (!(ext4_li_info->li_state & EXT4_LAZYINIT_RUNNING)) {
>  		ret = ext4_run_lazyinit_thread();
> 

Good catch. Thanks, the patch looks good.

-Lukas

Re: [PATCH] ext4: Fix a double free in ext4_register_li_request.

[Ted Ts'o]

On Mon, Mar 28, 2011 at 03:37:37PM +0800, Tao Ma wrote:
> From: Tao Ma <boyu.mt@taobao.com>
> 
> In ext4_register_li_request, we malloc a ext4_li_request and
> inserts it into ext4_li_info->li_request_list. In case of any
> error later, we free it in the end. But if we have some error
> in ext4_run_lazyinit_thread, the whole li_request_list will be
> dropped and freed in it. So we will double free this ext4_li_request.
> 
> This patch just sets elr to NULL after it is inserted to the list
> so that the latter kfree won't double free it.
> 
> Cc: stable@kernel.org
> Signed-off-by: Tao Ma <boyu.mt@taobao.com>

Thanks, I've added this to the ext4 tree for 2.6.39-rcX.

	     	   	       	    - Ted