Re: [PATCH] rose: fix OOB read on short CLEAR REQUEST frames.

[Eric Dumazet]

On Wed, Apr 8, 2026 at 6:32 PM Ashutosh Desai
<ashutoshdesai993@xxxxxxxxx> wrote:
>
> rose_process_rx_frame() dispatches to state machines after calling
> rose_decode(), but does not verify the frame is long enough before
> doing so. All five state machine handlers read skb->data[3] and
> skb->data[4] (cause and diagnostic bytes) when handling a
> ROSE_CLEAR_REQUEST frame, yet the only upstream length check is
> ROSE_MIN_LEN (3 bytes) in rose_route_frame().
>
> A crafted 3-byte ROSE CLEAR REQUEST frame (bytes: GFI/LCI-high,
> LCI-low, 0x13) passes the minimum length gate and reaches the state
> machines, where skb->data[3] and skb->data[4] are read one and two
> bytes past the valid buffer respectively.
>
> Add a check in rose_process_rx_frame() that drops any CLEAR REQUEST
> frame shorter than 5 bytes (3-byte header + cause + diagnostic),
> covering all five state machines with a single guard.
>
> Signed-off-by: Ashutosh Desai <ashutoshdesai993@xxxxxxxxx>
> ---
>  net/rose/rose_in.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/net/rose/rose_in.c b/net/rose/rose_in.c
> index 0276b393f..1ac9a6aee 100644
> --- a/net/rose/rose_in.c
> +++ b/net/rose/rose_in.c
> @@ -271,6 +271,11 @@ int rose_process_rx_frame(struct sock *sk, struct sk_buff *skb)
>
>         frametype = rose_decode(skb, &ns, &nr, &q, &d, &m);
>
> +       if (frametype == ROSE_CLEAR_REQUEST && skb->len < 5) {
> +               kfree_skb(skb);
> +               return 0;
> +       }
> +

Same answer: Testing skb->len alone is not enough.

skbs can have fragments, pskb_may_pull() or skb_linearize() would be needed.