Re: [PATCH 3.14 21/29] netfilter: x_tables: validate targets of jumps

Florian Westphal
2016-06-23T09:13:55Z

Florian Westphal <fw@strlen.de> wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > 3.14-stable review patch. If anyone has any objections, please let me know.
>
> I have -- this doesn't work in 3.14 as t->entries (the ruleset blob)
> is still kept percpu.
>
> > +static bool find_jump_target(const struct xt_table_info *t,
> > + const struct arpt_entry *target)
> > +{
> > + struct arpt_entry *iter;
> > +
> > + xt_entry_foreach(iter, t->entries, t->size) {
>
>
> .. so this causes in kernel soft lockup when I try to insert a rule.
>
> I will go over the 3.14 stable queue and see if I can amend this to work
> with 3.14.

This amended patch works for me (iptables-test.py passes except those
tests that I expected to fail due to some missing features in 3.14).

I also briefly tried 32bit iptables/ip6tables and that seems happy
as well. The reproduces for the two bugs fail with -EINVAL.

ebtables doesn't work (even ebtables -A INPUT -j ACCEPT fails), but
that should be solved by picking up
d26e2c9ffa385dd1b646f43c1397ba12af9e, "Revert "netfilter: ensure number
of counters is >0 in do_replace()" [ its a PARTIAL revert, so don't drop
the original patch ... ]

Subject: netfilter: x_tables: validate targets of jumps

commit 36472341017529e2b12573093cc0f68719300997 upstream.

When we see a jump also check that the offset gets us to beginning of
a rule (an ipt_entry).

The extra overhead is negible, even with absurd cases.

300k custom rules, 300k jumps to 'next' user chain:
[ plus one jump from INPUT to first userchain ]:

Before:
real 0m24.874s
user 0m7.532s
sys 0m16.076s

After:
real 0m27.464s
user 0m7.436s
sys 0m18.840s

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>
---
Need to pass the start of the ruleset as extra argument as
t->entries won't work in 3.14 (its percpu and not even set
up for all processors at this point).

net/ipv4/netfilter/arp_tables.c | 17 +++++++++++++++++
net/ipv4/netfilter/ip_tables.c | 17 +++++++++++++++++
net/ipv6/netfilter/ip6_tables.c | 17 +++++++++++++++++
3 files changed, 51 insertions(+)

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 993da4a..5f3e807 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -363,6 +363,19 @@ static inline bool unconditional(const struct arpt_entry *e)
memcmp(&e->arp, &uncond, sizeof(uncond)) == 0;
}

+static bool find_jump_target(const struct xt_table_info *t,
+ const void *entry0,
+ const struct arpt_entry *target)
+{
+ struct arpt_entry *iter;
+
+ xt_entry_foreach(iter, entry0, t->size) {
+ if (iter == target)
+ return true;
+ }
+ return false;
+}
+
/* Figures out from what hook each rule can be called: returns 0 if
* there are loops. Puts hook bitmask in comefrom.
*/
@@ -456,6 +469,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
/* This a jump; chase it. */
duprintf("Jump rule %u -> %u\n",
pos, newpos);
+ e = (struct arpt_entry *)
+ (entry0 + newpos);
+ if (!find_jump_target(newinfo, entry0, e))
+ return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index b75c5bb..f402317 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -439,6 +439,19 @@ ipt_do_table(struct sk_buff *skb,
#endif
}

+static bool find_jump_target(const struct xt_table_info *t,
+ const void *entry0,
+ const struct ipt_entry *target)
+{
+ struct ipt_entry *iter;
+
+ xt_entry_foreach(iter, entry0, t->size) {
+ if (iter == target)
+ return true;
+ }
+ return false;
+}
+
/* Figures out from what hook each rule can be called: returns 0 if
there are loops. Puts hook bitmask in comefrom. */
static int
@@ -536,6 +549,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
/* This a jump; chase it. */
duprintf("Jump rule %u -> %u\n",
pos, newpos);
+ e = (struct ipt_entry *)
+ (entry0 + newpos);
+ if (!find_jump_target(newinfo, entry0, e))
+ return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 9367bbd..e312639 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -449,6 +449,19 @@ ip6t_do_table(struct sk_buff *skb,
#endif
}

+static bool find_jump_target(const struct xt_table_info *t,
+ const void *entry0,
+ const struct ip6t_entry *target)
+{
+ struct ip6t_entry *iter;
+
+ xt_entry_foreach(iter, entry0, t->size) {
+ if (iter == target)
+ return true;
+ }
+ return false;
+}
+
/* Figures out from what hook each rule can be called: returns 0 if
there are loops. Puts hook bitmask in comefrom. */
static int
@@ -546,6 +559,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
/* This a jump; chase it. */
duprintf("Jump rule %u -> %u\n",
pos, newpos);
+ e = (struct ip6t_entry *)
+ (entry0 + newpos);
+ if (!find_jump_target(newinfo, entry0, e))
+ return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;
--
2.7.3