netdev - [PATCH net 3/3] sch_cake: Fix out of bounds when parsing TCP options

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Date:   Wed, 9 Jun 2021 17:22:12 +0300
From:   Maxim Mikityanskiy <maximmi@...dia.com>
To:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        "Jamal Hadi Salim" <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Patrick McHardy <kaber@...sh.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Peter Krystad <peter.krystad@...ux.intel.com>
CC:     Young Xiao <92siuyang@...il.com>, <netdev@...r.kernel.org>,
        "Maxim Mikityanskiy" <maximmi@...dia.com>
Subject: [PATCH net 3/3] sch_cake: Fix out of bounds when parsing TCP options

The TCP option parser in cake qdisc (cake_get_tcpopt and
cake_tcph_may_drop) 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 <92siuyang@...il.com>
Fixes: 8b7138814f29 ("sch_cake: Add optional ACK filter")
Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
---
 net/sched/sch_cake.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 7d37638ee1c7..6b03eebf0a78 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -967,6 +967,8 @@ static const void *cake_get_tcpopt(const struct tcphdr *tcph,
 			length--;
 			continue;
 		}
+		if (length < 2)
+			break;
 		opsize = *ptr++;
 		if (opsize < 2 || opsize > length)
 			break;
@@ -1104,6 +1106,8 @@ static bool cake_tcph_may_drop(const struct tcphdr *tcph,
 			length--;
 			continue;
 		}
+		if (length < 2)
+			break;
 		opsize = *ptr++;
 		if (opsize < 2 || opsize > length)
 			break;
-- 
2.25.1