[PATCH 4.4 73/75] netfilter: x_tables: check for bogus target offset

Greg Kroah-Hartman
2016-06-22T22:42:16Z

From: Florian Westphal <fw@strlen.de>

commit ce683e5f9d045e5d67d1312a42b359cb2ab2a13c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/netfilter/x_tables.h | 4 ++--
net/ipv4/netfilter/arp_tables.c | 5 +++--
net/ipv4/netfilter/ip_tables.c | 5 +++--
net/ipv6/netfilter/ip6_tables.c | 5 +++--
net/netfilter/x_tables.c | 17 +++++++++++++++--
5 files changed, 26 insertions(+), 10 deletions(-)

--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -239,7 +239,7 @@ void xt_unregister_match(struct xt_match
int xt_register_matches(struct xt_match *match, unsigned int n);
void xt_unregister_matches(struct xt_match *match, unsigned int n);

-int xt_check_entry_offsets(const void *base,
+int xt_check_entry_offsets(const void *base, const char *elems,
unsigned int target_offset,
unsigned int next_offset);

@@ -492,7 +492,7 @@ void xt_compat_target_from_user(struct x
unsigned int *size);
int xt_compat_target_to_user(const struct xt_entry_target *t,
void __user **dstptr, unsigned int *size);
-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);

--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -592,7 +592,8 @@ static inline int check_entry_size_and_h
if (!arp_checkentry(&e->arp))
return -EINVAL;

- err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
+ err = xt_check_entry_offsets(e, e->elems, e->target_offset,
+ e->next_offset);
if (err)
return err;

@@ -1253,7 +1254,7 @@ check_compat_entry_size_and_hooks(struct
if (!arp_checkentry(&e->arp))
return -EINVAL;

- ret = xt_compat_check_entry_offsets(e, e->target_offset,
+ ret = xt_compat_check_entry_offsets(e, e->elems, e->target_offset,
e->next_offset);
if (ret)
return ret;
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -754,7 +754,8 @@ check_entry_size_and_hooks(struct ipt_en
if (!ip_checkentry(&e->ip))
return -EINVAL;

- err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
+ err = xt_check_entry_offsets(e, e->elems, e->target_offset,
+ e->next_offset);
if (err)
return err;

@@ -1512,7 +1513,7 @@ check_compat_entry_size_and_hooks(struct
if (!ip_checkentry(&e->ip))
return -EINVAL;

- ret = xt_compat_check_entry_offsets(e,
+ ret = xt_compat_check_entry_offsets(e, e->elems,
e->target_offset, e->next_offset);
if (ret)
return ret;
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -766,7 +766,8 @@ check_entry_size_and_hooks(struct ip6t_e
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;

- err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
+ err = xt_check_entry_offsets(e, e->elems, e->target_offset,
+ e->next_offset);
if (err)
return err;

@@ -1524,7 +1525,7 @@ check_compat_entry_size_and_hooks(struct
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;

- ret = xt_compat_check_entry_offsets(e,
+ ret = xt_compat_check_entry_offsets(e, e->elems,
e->target_offset, e->next_offset);
if (ret)
return ret;
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -545,14 +545,17 @@ struct compat_xt_standard_target {
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;

@@ -576,12 +579,16 @@ EXPORT_SYMBOL(xt_compat_check_entry_offs
* 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
@@ -590,12 +597,18 @@ EXPORT_SYMBOL(xt_compat_check_entry_offs
* 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;