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

[Ashutosh Desai]

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;
+	}
+
 	switch (rose->state) {
 	case ROSE_STATE_1:
 		queued = rose_state1_machine(sk, skb, frametype);
-- 
2.34.1