Commit c4c07b4d authored Feb 06, 2019 by Jann Horn Committed by Pablo Neira Ayuso Feb 11, 2019

netfilter: nf_nat_snmp_basic: add missing length checks in ASN.1 cbs



The generic ASN.1 decoder infrastructure doesn't guarantee that callbacks
will get as much data as they expect; callbacks have to check the `datalen`
parameter before looking at `data`. Make sure that snmp_version() and
snmp_helper() don't read/write beyond the end of the packet data.

(Also move the assignment to `pdata` down below the check to make it clear
that it isn't necessarily a pointer we can use before the `datalen` check.)

Fixes: cc2d5863 ("netfilter: nf_nat_snmp_basic: use asn1 decoder library")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent 31b58ad0

net/ipv4/netfilter/nf_nat_snmp_basic_main.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -105,6 +105,8 @@ static void fast_csum(struct snmp_ctx *ctx, unsigned char offset)
		int snmp_version(void *context, size_t hdrlen, unsigned char tag,
		const void *data, size_t datalen)
		{
		if (datalen != 1)
		return -EINVAL;
		if ((unsigned char )data > 1)
		return -ENOTSUPP;
		return 1;
		@@ -114,8 +116,11 @@ int snmp_helper(void *context, size_t hdrlen, unsigned char tag,
		const void *data, size_t datalen)
		{
		struct snmp_ctx ctx = (struct snmp_ctx )context;
		__be32 pdata = (__be32 )data;
		__be32 *pdata;

		if (datalen != 4)
		return -EINVAL;
		pdata = (__be32 *)data;
		if (*pdata == ctx->from) {
		pr_debug("%s: %pI4 to %pI4\n", __func__,
		(void )&ctx->from, (void )&ctx->to);