[PATCH 6.12 064/460] netfilter: x_tables: guard option walkers against 1-byte tail reads

Greg Kroah-Hartman
2026-03-23T14:15:41Z

6.12-stable review patch. If anyone has any objections, please let me know.

------------------

From: David Dull <monderasdor@gmail.com>

[ Upstream commit cfe770220ac2dbd3e104c6b45094037455da81d4 ]

When the last byte of options is a non-single-byte option kind, walkers
that advance with i += op[i + 1] ? : 1 can read op[i + 1] past the end
of the option area.

Add an explicit i == optlen - 1 check before dereferencing op[i + 1]
in xt_tcpudp and xt_dccp option walkers.

Fixes: 2e4e6a17af35 ("[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables")
Signed-off-by: David Dull <monderasdor@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/xt_dccp.c | 4 ++--
net/netfilter/xt_tcpudp.c | 6 ++++--
2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/xt_dccp.c b/net/netfilter/xt_dccp.c
index e5a13ecbe67a0..037ab93e25d0a 100644
--- a/net/netfilter/xt_dccp.c
+++ b/net/netfilter/xt_dccp.c
@@ -62,10 +62,10 @@ dccp_find_option(u_int8_t option,
return true;
}

- if (op[i] < 2)
+ if (op[i] < 2 || i == optlen - 1)
i++;
else
- i += op[i+1]?:1;
+ i += op[i + 1] ? : 1;
}

spin_unlock_bh(&dccp_buflock);
diff --git a/net/netfilter/xt_tcpudp.c b/net/netfilter/xt_tcpudp.c
index e8991130a3de0..f76cf18f1a244 100644
--- a/net/netfilter/xt_tcpudp.c
+++ b/net/netfilter/xt_tcpudp.c
@@ -59,8 +59,10 @@ tcp_find_option(u_int8_t option,

for (i = 0; i < optlen; ) {
if (op[i] == option) return !invert;
- if (op[i] < 2) i++;
- else i += op[i+1]?:1;
+ if (op[i] < 2 || i == optlen - 1)
+ i++;
+ else
+ i += op[i + 1] ? : 1;
}

return invert;
--
2.51.0