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    Subject[PATCH 4.15 108/146] netfilter: add back stackpointer size checks
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Florian Westphal <fw@strlen.de>

    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.

    Fixes: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
    Reported-by: syzbot+e783f671527912cd9403@syzkaller.appspotmail.com
    Signed-off-by: Florian Westphal <fw@strlen.de>
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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(-)

    --- a/net/ipv4/netfilter/arp_tables.c
    +++ b/net/ipv4/netfilter/arp_tables.c
    @@ -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;
    }

    --- a/net/ipv4/netfilter/ip_tables.c
    +++ b/net/ipv4/netfilter/ip_tables.c
    @@ -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;
    --- a/net/ipv6/netfilter/ip6_tables.c
    +++ b/net/ipv6/netfilter/ip6_tables.c
    @@ -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;
    }


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