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Commit a919af8f authored by Florian Westphal's avatar Florian Westphal Committed by Srinivasa Rao Kuppala
Browse files

netfilter: add back stackpointer size checks 



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: 7814b6ec ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: default avatar <syzbot+e783f671527912cd9403@syzkaller.appspotmail.com>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8
[srkupp@codeaurora.org: Resolved minor conflict]
Signed-off-by: default avatarSrinivasa Rao Kuppala <srkupp@codeaurora.org>
Change-Id: I417d9164f95aae0d4ca2164a26d5d2fb7ec1ab10
parent cb2e955c

net/ipv4/netfilter/arp_tables.c

+4 −0
Original line number Diff line number Diff line
@@ -329,6 +329,10 @@ 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;

			}

net/ipv4/netfilter/ip_tables.c

+4 −2
Original line number Diff line number Diff line
@@ -408,9 +408,11 @@ ipt_do_table(struct sk_buff *skb, 
			}

			if (table_base + v != ipt_next_entry(e) &&

			    !(e->ip.flags & IPT_F_GOTO)) {

				if (unlikely(stackidx >= private->stacksize)) {

					verdict = NF_DROP;

					break;

				}

				jumpstack[stackidx++] = e;

				pr_debug("Pushed %p into pos %u\n",

					 e, stackidx - 1);

			}



			e = get_entry(table_base, v);

net/ipv6/netfilter/ip6_tables.c

+4 −0
Original line number Diff line number Diff line
@@ -429,6 +429,10 @@ 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;

			}