[PATCH 6.19 141/220] netfilter: nf_conntrack_h323: check for zero length in DecodeQ931()

Greg Kroah-Hartman
2026-03-23T13:56:38Z

From: Jenny Guanni Qu <qguanni@gmail.com>

[ Upstream commit f173d0f4c0f689173f8cdac79991043a4a89bf66 ]

In DecodeQ931(), the UserUserIE code path reads a 16-bit length from
the packet, then decrements it by 1 to skip the protocol discriminator
byte before passing it to DecodeH323_UserInformation(). If the encoded
length is 0, the decrement wraps to -1, which is then passed as a
large value to the decoder, leading to an out-of-bounds read.

Add a check to ensure len is positive after the decrement.

Fixes: 5e35941d9901 ("[NETFILTER]: Add H.323 conntrack/NAT helper")
Reported-by: Klaudia Kloc <klaudia@vidocsecurity.com>
Reported-by: Dawid Moczadło <dawid@vidocsecurity.com>
Tested-by: Jenny Guanni Qu <qguanni@gmail.com>
Signed-off-by: Jenny Guanni Qu <qguanni@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_conntrack_h323_asn1.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/netfilter/nf_conntrack_h323_asn1.c b/net/netfilter/nf_conntrack_h323_asn1.c
index c972e9488e16f..7b1497ed97d26 100644
--- a/net/netfilter/nf_conntrack_h323_asn1.c
+++ b/net/netfilter/nf_conntrack_h323_asn1.c
@@ -924,6 +924,8 @@ int DecodeQ931(unsigned char *buf, size_t sz, Q931 *q931)
break;
p++;
len--;
+ if (len <= 0)
+ break;
return DecodeH323_UserInformation(buf, p, len,
&q931->UUIE);
}
--
2.51.0