Re: [PATCH v2 06/25] ext4: aovid use-after-free in ext4_ext_insert_extent()

Jan Kara
2024-08-27T18:07:32Z

On Thu 22-08-24 10:35:26, libaokun@huaweicloud.com wrote:
> From: Baokun Li <libaokun1@huawei.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@linux.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@kernel.org
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.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@suse.com>
SUSE Labs, CR