netfilter: x_tables: check for bogus target offset
We're currently asserting that targetoff + targetsize <= nextoff.
Extend it to also check that targetoff is >= sizeof(xt_entry).
Since this is generic code, add an argument pointing to the start of the
match/target, we can then derive the base structure size from the delta.
We also need the e->elems pointer in a followup change to validate matches.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 1cb7a27..e2a6f2a 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -546,14 +546,17 @@
compat_uint_t verdict;
};
-/* see xt_check_entry_offsets */
-int xt_compat_check_entry_offsets(const void *base,
+int xt_compat_check_entry_offsets(const void *base, const char *elems,
unsigned int target_offset,
unsigned int next_offset)
{
+ long size_of_base_struct = elems - (const char *)base;
const struct compat_xt_entry_target *t;
const char *e = base;
+ if (target_offset < size_of_base_struct)
+ return -EINVAL;
+
if (target_offset + sizeof(*t) > next_offset)
return -EINVAL;
@@ -577,12 +580,16 @@
* xt_check_entry_offsets - validate arp/ip/ip6t_entry
*
* @base: pointer to arp/ip/ip6t_entry
+ * @elems: pointer to first xt_entry_match, i.e. ip(6)t_entry->elems
* @target_offset: the arp/ip/ip6_t->target_offset
* @next_offset: the arp/ip/ip6_t->next_offset
*
* validates that target_offset and next_offset are sane.
* Also see xt_compat_check_entry_offsets for CONFIG_COMPAT version.
*
+ * This function does not validate the targets or matches themselves, it
+ * only tests that all the offsets and sizes are correct.
+ *
* The arp/ip/ip6t_entry structure @base must have passed following tests:
* - it must point to a valid memory location
* - base to base + next_offset must be accessible, i.e. not exceed allocated
@@ -591,12 +598,18 @@
* Return: 0 on success, negative errno on failure.
*/
int xt_check_entry_offsets(const void *base,
+ const char *elems,
unsigned int target_offset,
unsigned int next_offset)
{
+ long size_of_base_struct = elems - (const char *)base;
const struct xt_entry_target *t;
const char *e = base;
+ /* target start is within the ip/ip6/arpt_entry struct */
+ if (target_offset < size_of_base_struct)
+ return -EINVAL;
+
if (target_offset + sizeof(*t) > next_offset)
return -EINVAL;
