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netfilter: x_tables: validate targets of jumps

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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>
This commit is contained in:
Florian Westphal 2016-04-01 14:17:22 +02:00 committed by Pablo Neira Ayuso
parent f24e230d25
commit 3647234101
3 changed files with 48 additions and 0 deletions
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16
net/ipv4/netfilter/arp_tables.c
View File

@ -367,6 +367,18 @@ 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 struct arpt_entry *target)
{
struct arpt_entry *iter;
xt_entry_foreach(iter, t->entries, 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.
*/
@ -460,6 +472,10 @@ 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, e))
return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;

16
net/ipv4/netfilter/ip_tables.c
View File

@ -443,6 +443,18 @@ ipt_do_table(struct sk_buff *skb,
#endif
}
static bool find_jump_target(const struct xt_table_info *t,
const struct ipt_entry *target)
{
struct ipt_entry *iter;
xt_entry_foreach(iter, t->entries, 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
@ -540,6 +552,10 @@ 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, e))
return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;

16
net/ipv6/netfilter/ip6_tables.c
View File

@ -455,6 +455,18 @@ ip6t_do_table(struct sk_buff *skb,
#endif
}
static bool find_jump_target(const struct xt_table_info *t,
const struct ip6t_entry *target)
{
struct ip6t_entry *iter;
xt_entry_foreach(iter, t->entries, 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
@ -552,6 +564,10 @@ 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, e))
return 0;
} else {
/* ... this is a fallthru */
newpos = pos + e->next_offset;