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: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: syzbot+e783f671527912cd9...@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <f...@strlen.de>
---
net/ipv4/netfilter/arp_tables.c | 4 ++++
net/ipv4/netfilter/ip_tables.c | 7 ++++++-
net/ipv6/netfilter/ip6_tables.c | 4 ++++
3 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 4ffe302f9b82..e3e420f3ba7b 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -252,6 +252,10 @@ unsigned int arpt_do_table(struct sk_buff *skb,
}
if (table_base + v
!= arpt_next_entry(e)) {
+ if (unlikely(stackidx >= private->stacksize)) {
+ verdict = NF_DROP;
+ break;
+ }
jumpstack[stackidx++] = e;
}
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 9a71f3149507..e38395a8dcf2 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -330,8 +330,13 @@ ipt_do_table(struct sk_buff *skb,
continue;
}
if (table_base + v != ipt_next_entry(e) &&
- !(e->ip.flags & IPT_F_GOTO))
+ !(e->ip.flags & IPT_F_GOTO)) {
+ if (unlikely(stackidx >= private->stacksize)) {
+ verdict = NF_DROP;
+ break;
+ }
jumpstack[stackidx++] = e;
+ }
e = get_entry(table_base, v);
continue;
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index af4c917e0836..62358b93bbac 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -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;
}
--
2.13.6
--
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