On Wed, Apr 14, 2021 at 11:57:59AM +0300, Dan Carpenter wrote:
> The bounds checking in avc_ca_pmt() is not strict enough. It should
> be checking "read_pos + 4" because it's reading 5 bytes. If the
> "es_info_length" is non-zero then it reads a 6th byte so there needs to
> be an additional check for that.
>
> I also added checks for the "write_pos". I don't think these are
> required because "read_pos" and "write_pos" are tied together so
> checking one ought to be enough. But they make the code easier to
> understand for me.
>
> The other problem is that "length" can be invalid. It comes from
> "data_length" in fdtv_ca_pmt().
>
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Luo Likang <luolikang@xxxxxxxxxxx>
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Thanks for the report and the fix!
As a quick note on alternative mitigations, it seems that
CONFIG_UBSAN_BOUNDS would have caught this at runtime too. (i.e.
c->operand[]'s size is known at build time, so out of bounds
indexing should be detected.)
-Kees
> ---
> This hardware isn't super common so there is no embargo. Resending
> through normal lists.
>
> Oh, another thing is the data_length calculation in fdtv_ca_pmt() seems
> very suspicous. Reading more than 4 bytes in the loop will lead to
> shift wrapping.
>
> drivers/media/firewire/firedtv-avc.c | 14 +++++++++++---
> drivers/media/firewire/firedtv-ci.c | 2 ++
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/firewire/firedtv-avc.c b/drivers/media/firewire/firedtv-avc.c
> index 2bf9467b917d..71991f8638e6 100644
> --- a/drivers/media/firewire/firedtv-avc.c
> +++ b/drivers/media/firewire/firedtv-avc.c
> @@ -1165,7 +1165,11 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length)
> read_pos += program_info_length;
> write_pos += program_info_length;
> }
> - while (read_pos < length) {
> + while (read_pos + 4 < length) {
> + if (write_pos + 4 >= sizeof(c->operand) - 4) {
> + ret = -EINVAL;
> + goto out;
> + }
> c->operand[write_pos++] = msg[read_pos++];
> c->operand[write_pos++] = msg[read_pos++];
> c->operand[write_pos++] = msg[read_pos++];
> @@ -1177,13 +1181,17 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length)
> c->operand[write_pos++] = es_info_length >> 8;
> c->operand[write_pos++] = es_info_length & 0xff;
> if (es_info_length > 0) {
> + if (read_pos >= length) {
> + ret = -EINVAL;
> + goto out;
> + }
> pmt_cmd_id = msg[read_pos++];
> if (pmt_cmd_id != 1 && pmt_cmd_id != 4)
> dev_err(fdtv->device, "invalid pmt_cmd_id %d at stream level\n",
> pmt_cmd_id);
>
> - if (es_info_length > sizeof(c->operand) - 4 -
> - write_pos) {
> + if (es_info_length > sizeof(c->operand) - 4 - write_pos ||
> + es_info_length > length - read_pos) {
> ret = -EINVAL;
> goto out;
> }
> diff --git a/drivers/media/firewire/firedtv-ci.c b/drivers/media/firewire/firedtv-ci.c
> index 9363d005e2b6..2d6992ac5dd6 100644
> --- a/drivers/media/firewire/firedtv-ci.c
> +++ b/drivers/media/firewire/firedtv-ci.c
> @@ -134,6 +134,8 @@ static int fdtv_ca_pmt(struct firedtv *fdtv, void *arg)
> } else {
> data_length = msg->msg[3];
> }
> + if (data_length > sizeof(msg->msg) - 4)
> + return -EINVAL;
>
> return avc_ca_pmt(fdtv, &msg->msg[data_pos], data_length);
> }
> --
> 2.30.2
>
--
Kees Cook
