[PATCH 4.6 73/81] netfilter: x_tables: add and use xt_check_entry_offsets

Greg Kroah-Hartman
2016-06-22T22:48:20Z

From: Florian Westphal <fw@strlen.de>

commit 7d35812c3214afa5b37a675113555259cfd67b98 upstream.

Currently arp/ip and ip6tables each implement a short helper to check that
the target offset is large enough to hold one xt_entry_target struct and
that t->u.target_size fits within the current rule.

Unfortunately these checks are not sufficient.

To avoid adding new tests to all of ip/ip6/arptables move the current
checks into a helper, then extend this helper in followup patches.

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 | 11 +----------
net/ipv4/netfilter/ip_tables.c | 12 +-----------
net/ipv6/netfilter/ip6_tables.c | 12 +-----------
net/netfilter/x_tables.c | 34 ++++++++++++++++++++++++++++++++++
5 files changed, 41 insertions(+), 32 deletions(-)

--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -242,6 +242,10 @@ 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,
+ unsigned int target_offset,
+ unsigned int next_offset);
+
int xt_check_match(struct xt_mtchk_param *, unsigned int size, u_int8_t proto,
bool inv_proto);
int xt_check_target(struct xt_tgchk_param *, unsigned int size, u_int8_t proto,
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -496,19 +496,10 @@ next:

static inline int check_entry(const struct arpt_entry *e)
{
- const struct xt_entry_target *t;
-
if (!arp_checkentry(&e->arp))
return -EINVAL;

- if (e->target_offset + sizeof(struct xt_entry_target) > e->next_offset)
- return -EINVAL;
-
- t = arpt_get_target_c(e);
- if (e->target_offset + t->u.target_size > e->next_offset)
- return -EINVAL;
-
- return 0;
+ return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}

static inline int check_target(struct arpt_entry *e, const char *name)
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -590,20 +590,10 @@ static void cleanup_match(struct xt_entr
static int
check_entry(const struct ipt_entry *e)
{
- const struct xt_entry_target *t;
-
if (!ip_checkentry(&e->ip))
return -EINVAL;

- if (e->target_offset + sizeof(struct xt_entry_target) >
- e->next_offset)
- return -EINVAL;
-
- t = ipt_get_target_c(e);
- if (e->target_offset + t->u.target_size > e->next_offset)
- return -EINVAL;
-
- return 0;
+ return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}

static int
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -602,20 +602,10 @@ static void cleanup_match(struct xt_entr
static int
check_entry(const struct ip6t_entry *e)
{
- const struct xt_entry_target *t;
-
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;

- if (e->target_offset + sizeof(struct xt_entry_target) >
- e->next_offset)
- return -EINVAL;
-
- t = ip6t_get_target_c(e);
- if (e->target_offset + t->u.target_size > e->next_offset)
- return -EINVAL;
-
- return 0;
+ return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}

static int check_match(struct xt_entry_match *m, struct xt_mtchk_param *par)
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -541,6 +541,40 @@ int xt_compat_match_to_user(const struct
EXPORT_SYMBOL_GPL(xt_compat_match_to_user);
#endif /* CONFIG_COMPAT */

+/**
+ * xt_check_entry_offsets - validate arp/ip/ip6t_entry
+ *
+ * @base: pointer to arp/ip/ip6t_entry
+ * @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.
+ *
+ * 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
+ * length.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int xt_check_entry_offsets(const void *base,
+ unsigned int target_offset,
+ unsigned int next_offset)
+{
+ const struct xt_entry_target *t;
+ const char *e = base;
+
+ if (target_offset + sizeof(*t) > next_offset)
+ return -EINVAL;
+
+ t = (void *)(e + target_offset);
+ if (target_offset + t->u.target_size > next_offset)
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL(xt_check_entry_offsets);
+
int xt_check_target(struct xt_tgchk_param *par,
unsigned int size, u_int8_t proto, bool inv_proto)
{