[PATCH net v2 2/3] mptcp: Fix out of bounds when parsing TCP options

The TCP option parser in mptcp (mptcp_get_options) could read one byte
out of bounds. When the length is 1, the execution flow gets into the
loop, reads one byte of the opcode, and if the opcode is neither
TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the
length of 1.

This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack
out of bounds when parsing TCP options.").

Cc: Young Xiao <redacted>
Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections")
Signed-off-by: Maxim Mikityanskiy <redacted>
Reviewed-by: Mat Martineau <redacted>
---
 net/mptcp/options.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 6b825fb3fa83..9b263f27ce9b 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c

@@ -356,6 +356,8 @@ void mptcp_get_options(const struct sk_buff *skb,
 			length--;
 			continue;
 		default:
+			if (length < 2)
+				return;
 			opsize = *ptr++;
 			if (opsize < 2) /* "silly options" */
 				return;

-- 
2.25.1