Re: [PATCH v2 05/25] ext4: update orig_path in ext4_find_extent()

Jan Kara
2024-08-27T18:04:35Z

On Thu 22-08-24 10:35:25, libaokun@huaweicloud.com wrote:
> From: Baokun Li <libaokun1@huawei.com>
>
> In ext4_find_extent(), if the path is not big enough, we free it and set
> *orig_path to NULL. But after reallocating and successfully initializing
> the path, we don't update *orig_path, in which case the caller gets a
> valid path but a NULL ppath, and this may cause a NULL pointer dereference
> or a path memory leak. For example:
>
> ext4_split_extent
> path = *ppath = 2000
> ext4_find_extent
> if (depth > path[0].p_maxdepth)
> kfree(path = 2000);
> *orig_path = path = NULL;
> path = kcalloc() = 3000
> ext4_split_extent_at(*ppath = NULL)
> path = *ppath;
> ex = path[depth].p_ext;
> // NULL pointer dereference!
>
> ==================================================================
> BUG: kernel NULL pointer dereference, address: 0000000000000010
> CPU: 6 UID: 0 PID: 576 Comm: fsstress Not tainted 6.11.0-rc2-dirty #847
> RIP: 0010:ext4_split_extent_at+0x6d/0x560
> Call Trace:
> <TASK>
> ext4_split_extent.isra.0+0xcb/0x1b0
> ext4_ext_convert_to_initialized+0x168/0x6c0
> ext4_ext_handle_unwritten_extents+0x325/0x4d0
> ext4_ext_map_blocks+0x520/0xdb0
> ext4_map_blocks+0x2b0/0x690
> ext4_iomap_begin+0x20e/0x2c0
> [...]
> ==================================================================
>
> Therefore, *orig_path is updated when the extent lookup succeeds, so that
> the caller can safely use path or *ppath.
>
> 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 | 3 ++-
> fs/ext4/move_extent.c | 1 -
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 0224cf0ef19e..5879aef159d8 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -957,6 +957,8 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
>
> ext4_ext_show_path(inode, path);
>
> + if (orig_path)
> + *orig_path = path;
> return path;
>
> err:
> @@ -3268,7 +3270,6 @@ static int ext4_split_extent_at(handle_t *handle,
> }
> depth = ext_depth(inode);
> ex = path[depth].p_ext;
> - *ppath = path;
>
> if (EXT4_EXT_MAY_ZEROOUT & split_flag) {
> if (split_flag & (EXT4_EXT_DATA_VALID1|EXT4_EXT_DATA_VALID2)) {
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index 204f53b23622..c95e3e526390 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -36,7 +36,6 @@ get_ext_path(struct inode *inode, ext4_lblk_t lblock,
> *ppath = NULL;
> return -ENODATA;
> }
> - *ppath = path;
> return 0;
> }
>
> --
> 2.39.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR