Patch "netfilter: add back stackpointer size checks" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

netfilter: add back stackpointer size checks

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netfilter-add-back-stackpointer-size-checks.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Florian Westphal <[email protected]>
Date: Wed, 7 Feb 2018 13:46:25 +0100
Subject: netfilter: add back stackpointer size checks

From: Florian Westphal <[email protected]>

commit 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8 upstream.

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.

---
 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(-)

@@ -257,6 +257,10 @@ unsigned int arpt_do_table(struct sk_buf
 			}
 			if (table_base + v
 			    != arpt_next_entry(e)) {
+				if (unlikely(stackidx >= private->stacksize)) {
+					verdict = NF_DROP;
+					break;
+				}
 				jumpstack[stackidx++] = e;
 			}
 

@@ -335,8 +335,13 @@ 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;

@@ -357,6 +357,10 @@ 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;
 			}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/netfilter-add-back-stackpointer-size-checks.patch queue-4.15/netfilter-ipv6-fix-use-after-free-write-in-nf_nat_ipv6_manip_pkt.patch queue-4.15/netfilter-ebtables-config_compat-don-t-trust-userland-offsets.patch queue-4.15/netfilter-bridge-ebt_among-add-missing-match-size-checks.patch