netfilter: nf_conntrack_h323: fix OOB read in decode_int() CONS case

[ Upstream commit 1e3a359 ]

In decode_int(), the CONS case calls get_bits(bs, 2) to read a length
value, then calls get_uint(bs, len) without checking that len bytes
remain in the buffer. The existing boundary check only validates the
2 bits for get_bits(), not the subsequent 1-4 bytes that get_uint()
reads. This allows a malformed H.323/RAS packet to cause a 1-4 byte
slab-out-of-bounds read.

Add a boundary check for len bytes after get_bits() and before
get_uint().

Fixes: 5e35941 ("[NETFILTER]: Add H.323 conntrack/NAT helper")
Reported-by: Klaudia Kloc <klaudia@vidocsecurity.com>
Reported-by: Dawid Moczadło <dawid@vidocsecurity.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>

Author: Jenny Guanni Qu

net/netfilter/nf_conntrack_h323_asn1.c

@@ -331,6 +331,8 @@ static int decode_int(struct bitstr *bs, const struct field_t *f,
 		if (nf_h323_error_boundary(bs, 0, 2))
 			return H323_ERROR_BOUND;
 		len = get_bits(bs, 2) + 1;
+		if (nf_h323_error_boundary(bs, len, 0))
+			return H323_ERROR_BOUND;
 		BYTE_ALIGN(bs);
 		if (base && (f->attr & DECODE)) {	/* timeToLive */
 			unsigned int v = get_uint(bs, len) + f->lb;