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netfilter: xtables: check for unconditionality of policies

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This adds a check that iptables's original author Rusty set forth in
a FIXME comment.

Underflows in iptables are better known as chain policies, and are
required to be unconditional or there would be a stochastical chance
for the policy rule to be skipped if it does not match. If that were
to happen, rule execution would continue in an unexpected spurious
fashion.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
This commit is contained in:
Jan Engelhardt 2009-07-09 22:54:53 +02:00
parent a7d51738e7
commit 90e7d4ab5c
3 changed files with 21 additions and 14 deletions
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12
net/ipv4/netfilter/arp_tables.c
View File

@ -8,7 +8,7 @@
* Copyright (C) 2002 David S. Miller (davem@redhat.com)
*
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
@ -563,13 +563,15 @@ static inline int check_entry_size_and_hooks(struct arpt_entry *e,
continue;
if ((unsigned char *)e - base == hook_entries[h])
newinfo->hook_entry[h] = hook_entries[h];
if ((unsigned char *)e - base == underflows[h])
if ((unsigned char *)e - base == underflows[h]) {
if (!unconditional(&e->arp)) {
pr_err("Underflows must be unconditional\n");
return -EINVAL;
}
newinfo->underflow[h] = underflows[h];
}
}
/* FIXME: underflows must be unconditional, standard verdicts
< 0 (not ARPT_RETURN). --RR */
/* Clear counters and comefrom */
e->counters = ((struct xt_counters) { 0, 0 });
e->comefrom = 0;

11
net/ipv4/netfilter/ip_tables.c
View File

@ -8,6 +8,7 @@
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/cache.h>
#include <linux/capability.h>
#include <linux/skbuff.h>
@ -738,13 +739,15 @@ check_entry_size_and_hooks(struct ipt_entry *e,
continue;
if ((unsigned char *)e - base == hook_entries[h])
newinfo->hook_entry[h] = hook_entries[h];
if ((unsigned char *)e - base == underflows[h])
if ((unsigned char *)e - base == underflows[h]) {
if (!unconditional(&e->ip)) {
pr_err("Underflows must be unconditional\n");
return -EINVAL;
}
newinfo->underflow[h] = underflows[h];
}
}
/* FIXME: underflows must be unconditional, standard verdicts
< 0 (not IPT_RETURN). --RR */
/* Clear counters and comefrom */
e->counters = ((struct xt_counters) { 0, 0 });
e->comefrom = 0;

12
net/ipv6/netfilter/ip6_tables.c
View File

@ -8,7 +8,7 @@
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/capability.h>
#include <linux/in.h>
#include <linux/skbuff.h>
@ -771,13 +771,15 @@ check_entry_size_and_hooks(struct ip6t_entry *e,
continue;
if ((unsigned char *)e - base == hook_entries[h])
newinfo->hook_entry[h] = hook_entries[h];
if ((unsigned char *)e - base == underflows[h])
if ((unsigned char *)e - base == underflows[h]) {
if (!unconditional(&e->ipv6)) {
pr_err("Underflows must be unconditional\n");
return -EINVAL;
}
newinfo->underflow[h] = underflows[h];
}
}
/* FIXME: underflows must be unconditional, standard verdicts
< 0 (not IP6T_RETURN). --RR */
/* Clear counters and comefrom */
e->counters = ((struct xt_counters) { 0, 0 });
e->comefrom = 0;