Re: [dm-devel] [PATCH v2 3/6] device-mapper: structs and parameter strings must not overlap

[Mikulas Patocka <mpatocka@redhat.com>]

On Sat, 3 Jun 2023, Demi Marie Obenour wrote:

> The NUL terminator for each target parameter string must precede the
> following 'struct dm_target_spec'.  Otherwise, dm_split_args() might
> corrupt this struct.  Furthermore, the first 'struct dm_target_spec'
> must come after the 'struct dm_ioctl', as if it overlaps too much
> dm_split_args() could corrupt the 'struct dm_ioctl'.
> 
> Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org

Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>

> ---
>  drivers/md/dm-ioctl.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 64e8f16d344c47057de5e2d29e3d63202197dca0..da6ca26b51d0953df380582bb3a51c2ec22c27cb 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1391,7 +1391,7 @@ static inline fmode_t get_mode(struct dm_ioctl *param)
>  	return mode;
>  }
>  
> -static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
> +static int next_target(struct dm_target_spec *last, uint32_t next, const char *end,
>  		       struct dm_target_spec **spec, char **target_params)
>  {
>  	static_assert(_Alignof(struct dm_target_spec) <= 8,
> @@ -1404,7 +1404,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
>  	 * sizeof(struct dm_target_spec) or more, as otherwise *last was
>  	 * out of bounds already.
>  	 */
> -	size_t remaining = (char *)end - (char *)last;
> +	size_t remaining = end - (char *)last;
>  
>  	/*
>  	 * There must be room for both the next target spec and the
> @@ -1423,10 +1423,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
>  	*spec = (struct dm_target_spec *) ((unsigned char *) last + next);
>  	*target_params = (char *) (*spec + 1);
>  
> -	if (*spec < (last + 1))
> -		return -EINVAL;
> -
> -	return invalid_str(*target_params, end);
> +	return 0;
>  }
>  
>  static int populate_table(struct dm_table *table,
> @@ -1436,8 +1433,9 @@ static int populate_table(struct dm_table *table,
>  	unsigned int i = 0;
>  	struct dm_target_spec *spec = (struct dm_target_spec *) param;
>  	uint32_t next = param->data_start;
> -	void *end = (void *) param + param_size;
> +	const char *const end = (const char *) param + param_size;
>  	char *target_params;
> +	size_t min_size = sizeof(struct dm_ioctl);
>  
>  	if (!param->target_count) {
>  		DMERR("%s: no targets specified", __func__);
> @@ -1445,6 +1443,13 @@ static int populate_table(struct dm_table *table,
>  	}
>  
>  	for (i = 0; i < param->target_count; i++) {
> +		const char *nul_terminator;
> +
> +		if (next < min_size) {
> +			DMERR("%s: next target spec (offset %u) overlaps %s",
> +			      __func__, next, i ? "previous target" : "'struct dm_ioctl'");
> +			return -EINVAL;
> +		}
>  
>  		r = next_target(spec, next, end, &spec, &target_params);
>  		if (r) {
> @@ -1452,6 +1457,15 @@ static int populate_table(struct dm_table *table,
>  			return r;
>  		}
>  
> +		nul_terminator = memchr(target_params, 0, (size_t)(end - target_params));
> +		if (nul_terminator == NULL) {
> +			DMERR("%s: target parameters not NUL-terminated", __func__);
> +			return -EINVAL;
> +		}
> +
> +		/* Add 1 for NUL terminator */
> +		min_size = (size_t)(nul_terminator - (const char *)spec) + 1;
> +
>  		r = dm_table_add_target(table, spec->target_type,
>  					(sector_t) spec->sector_start,
>  					(sector_t) spec->length,
> -- 
> Sincerely,
> Demi Marie Obenour (she/her/hers)
> Invisible Things Lab
> 
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