[PATCH 4.19 034/109] sch_cake: Fix out of bounds when parsing TCP options and header

[Sasha Levin]

From: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>

[ Upstream commit ba91c49dedbde758ba0b72f57ac90b06ddf8e548 ]

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.").

v2 changes:

Added doff validation in cake_get_tcphdr to avoid parsing garbage as TCP
header. Although it wasn't strictly an out-of-bounds access (memory was
allocated), garbage values could be read where CAKE expected the TCP
header if doff was smaller than 5.

Cc: Young Xiao <92siuyang@xxxxxxxxx>
Fixes: 8b7138814f29 ("sch_cake: Add optional ACK filter")
Signed-off-by: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/sched/sch_cake.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 32712e7dcbdc..2025f0f559de 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -900,7 +900,7 @@ static struct tcphdr *cake_get_tcphdr(const struct sk_buff *skb,
 	}
 
 	tcph = skb_header_pointer(skb, offset, sizeof(_tcph), &_tcph);
-	if (!tcph)
+	if (!tcph || tcph->doff < 5)
 		return NULL;
 
 	return skb_header_pointer(skb, offset,
@@ -924,6 +924,8 @@ static const void *cake_get_tcpopt(const struct tcphdr *tcph,
 			length--;
 			continue;
 		}
+		if (length < 2)
+			break;
 		opsize = *ptr++;
 		if (opsize < 2 || opsize > length)
 			break;
@@ -1061,6 +1063,8 @@ static bool cake_tcph_may_drop(const struct tcphdr *tcph,
 			length--;
 			continue;
 		}
+		if (length < 2)
+			break;
 		opsize = *ptr++;
 		if (opsize < 2 || opsize > length)
 			break;
-- 
2.30.2