linux-kernel - Re: [PATCH v2 06/25] ext4: aovid use-after-free in ext4_ext_insert

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Message-ID: <20240827180724.7y4qnopci6exggzj@quack3>
Date: Tue, 27 Aug 2024 20:07:24 +0200
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, ritesh.list@...il.com, ojaswin@...ux.ibm.com,
	linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
	yangerkun@...wei.com, Baokun Li <libaokun1@...wei.com>,
	stable@...nel.org
Subject: Re: [PATCH v2 06/25] ext4: aovid use-after-free in
 ext4_ext_insert_extent()

On Thu 22-08-24 10:35:26, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> As Ojaswin mentioned in Link, in ext4_ext_insert_extent(), if the path is
> reallocated in ext4_ext_create_new_leaf(), we'll use the stale path and
> cause UAF. Below is a sample trace with dummy values:
> 
> ext4_ext_insert_extent
>   path = *ppath = 2000
>   ext4_ext_create_new_leaf(ppath)
>     ext4_find_extent(ppath)
>       path = *ppath = 2000
>       if (depth > path[0].p_maxdepth)
>             kfree(path = 2000);
>             *ppath = path = NULL;
>       path = kcalloc() = 3000
>       *ppath = 3000;
>       return path;
>   /* here path is still 2000, UAF! */
>   eh = path[depth].p_hdr
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in ext4_ext_insert_extent+0x26d4/0x3330
> Read of size 8 at addr ffff8881027bf7d0 by task kworker/u36:1/179
> CPU: 3 UID: 0 PID: 179 Comm: kworker/u6:1 Not tainted 6.11.0-rc2-dirty #866
> Call Trace:
>  <TASK>
>  ext4_ext_insert_extent+0x26d4/0x3330
>  ext4_ext_map_blocks+0xe22/0x2d40
>  ext4_map_blocks+0x71e/0x1700
>  ext4_do_writepages+0x1290/0x2800
> [...]
> 
> Allocated by task 179:
>  ext4_find_extent+0x81c/0x1f70
>  ext4_ext_map_blocks+0x146/0x2d40
>  ext4_map_blocks+0x71e/0x1700
>  ext4_do_writepages+0x1290/0x2800
>  ext4_writepages+0x26d/0x4e0
>  do_writepages+0x175/0x700
> [...]
> 
> Freed by task 179:
>  kfree+0xcb/0x240
>  ext4_find_extent+0x7c0/0x1f70
>  ext4_ext_insert_extent+0xa26/0x3330
>  ext4_ext_map_blocks+0xe22/0x2d40
>  ext4_map_blocks+0x71e/0x1700
>  ext4_do_writepages+0x1290/0x2800
>  ext4_writepages+0x26d/0x4e0
>  do_writepages+0x175/0x700
> [...]
> ==================================================================
> 
> So use *ppath to update the path to avoid the above problem.
> 
> Reported-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Closes: https://lore.kernel.org/r/ZqyL6rmtwl6N4MWR@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com
> Fixes: 10809df84a4d ("ext4: teach ext4_ext_find_extent() to realloc path if necessary")
> Cc: stable@...nel.org
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/extents.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 5879aef159d8..91c6586afcca 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2116,6 +2116,7 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
>  				       ppath, newext);
>  	if (err)
>  		goto cleanup;
> +	path = *ppath;
>  	depth = ext_depth(inode);
>  	eh = path[depth].p_hdr;
>  
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR