[PATCH 4.19 033/109] netfilter: synproxy: Fix out of bounds when parsing TCP options

[Sasha Levin]

From: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>

[ Upstream commit 5fc177ab759418c9537433e63301096e733fb915 ]

The TCP option parser in synproxy (synproxy_parse_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.").

v2 changes:

Added an early return when length < 0 to avoid calling
skb_header_pointer with negative length.

Cc: Young Xiao <92siuyang@xxxxxxxxx>
Fixes: 48b1de4c110a ("netfilter: add SYNPROXY core/target")
Signed-off-by: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>
Reviewed-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/netfilter/nf_synproxy_core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 353a2aa80c3c..04b07b63c540 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -34,6 +34,9 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
 	int length = (th->doff * 4) - sizeof(*th);
 	u8 buf[40], *ptr;
 
+	if (unlikely(length < 0))
+		return false;
+
 	ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
 	if (ptr == NULL)
 		return false;
@@ -50,6 +53,8 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
 			length--;
 			continue;
 		default:
+			if (length < 2)
+				return true;
 			opsize = *ptr++;
 			if (opsize < 2)
 				return true;
-- 
2.30.2