4.19-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit c4c07b4d6fa1f11880eab8e076d3d060ef3f55fc upstream.
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: cc2d58634e0f ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/ipv4/netfilter/nf_nat_snmp_basic_main.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/net/ipv4/netfilter/nf_nat_snmp_basic_main.c +++ b/net/ipv4/netfilter/nf_nat_snmp_basic_main.c @@ -104,6 +104,8 @@ static void fast_csum(struct snmp_ctx *c 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; @@ -113,8 +115,11 @@ int snmp_helper(void *context, size_t hd 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);