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netfilter: add back stackpointer size checks

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The rationale for removing the check is only correct for rulesets
generated by ip(6)tables.

In iptables, a jump can only occur to a user-defined chain, i.e.
because we size the stack based on number of user-defined chains we
cannot exceed stack size.

However, the underlying binary format has no such restriction,
and the validation step only ensures that the jump target is a
valid rule start point.

IOW, its possible to build a rule blob that has no user-defined
chains but does contain a jump.

If this happens, no jump stack gets allocated and crash occurs
because no jumpstack was allocated.

Fixes: 7814b6ec6d ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: [email protected]
Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
This commit is contained in:
Florian Westphal 2018-02-07 13:46:25 +01:00 • committed by Pablo Neira Ayuso
commit 57ebd808a9
3 changed files with 14 additions and 1 deletions
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4
net/ipv6/netfilter/ip6_tables.c
View file

@ -352,6 +352,10 @@ ip6t_do_table(struct sk_buff *skb,
}
if (table_base + v != ip6t_next_entry(e) &&
!(e->ipv6.flags & IP6T_F_GOTO)) {
if (unlikely(stackidx >= private->stacksize)) {
verdict = NF_DROP;
break;
}
jumpstack[stackidx++] = e;
}