[PATCH v2] rose: fix OOB reads on short CLEAR REQUEST frames

[Ashutosh Desai <ashutoshdesai993@gmail.com>]

rose_process_rx_frame() calls rose_decode() which reads skb->data[2]
without any prior length check. For CLEAR REQUEST frames the state
machines then read skb->data[3] and skb->data[4] as the cause and
diagnostic bytes.

A crafted 3-byte ROSE CLEAR REQUEST frame passes the minimum length
gate in rose_route_frame() and reaches rose_process_rx_frame(), where
rose_decode() reads one byte past the header and the state machines
read two bytes past the valid buffer.

Add a pskb_may_pull(skb, 3) check before rose_decode() to cover its
skb->data[2] access, and a pskb_may_pull(skb, 5) check afterwards for
the CLEAR REQUEST path to cover the cause and diagnostic reads.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Ashutosh Desai <ashutoshdesai993@gmail.com>
---
V1 -> V2: switch skb->len check to pskb_may_pull; also add
          pskb_may_pull(skb, 3) before rose_decode() to cover its
          skb->data[2] access

v1: https://lore.kernel.org/netdev/20260409013246.2051746-1-ashutoshdesai993@gmail.com/

 net/rose/rose_in.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/rose/rose_in.c b/net/rose/rose_in.c
index 0276b393f0e5..b9f01a11e2df 100644
--- a/net/rose/rose_in.c
+++ b/net/rose/rose_in.c
@@ -269,8 +269,18 @@ int rose_process_rx_frame(struct sock *sk, struct sk_buff *skb)
 if (rose->state == ROSE_STATE_0)
  0;
 
+if (!pskb_may_pull(skb, 3)) {
+kfree_skb(skb);
+return 0;
+}
+
 frametype = rose_decode(skb, &ns, &nr, &q, &d, &m);
 
+if (frametype == ROSE_CLEAR_REQUEST && !pskb_may_pull(skb, 5)) {
+kfree_skb(skb);
+return 0;
+}
+
 switch (rose->state) {
 case ROSE_STATE_1:
 ueued = rose_state1_machine(sk, skb, frametype);
-- 
2.34.1