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    SubjectRe: [PATCH 3.10 007/180] netfilter: x_tables: validate targets of jumps
    On Sun, Aug 21, 2016 at 05:28:57PM +0200, Willy Tarreau wrote:
    > From: Florian Westphal <fw@strlen.de>
    >
    > commit 36472341017529e2b12573093cc0f68719300997 upstream.
    >
    > When we see a jump also check that the offset gets us to beginning of
    > a rule (an ipt_entry).
    (...)

    Sorry, this patch is bad and causes performance issues, I didn't notice
    that 3.14 had a different version, below. Thanks to Jay for reporting
    the problem to me. I'll push 3.10.103-rc2 after some cool down period.

    Willy

    ----

    From 3c079e0993ca3bdd94dddd028ee04c85911aa666 Mon Sep 17 00:00:00 2001
    From: Florian Westphal <fw@strlen.de>
    Date: Fri, 1 Apr 2016 14:17:22 +0200
    Subject: netfilter: x_tables: validate targets of jumps

    commit 36472341017529e2b12573093cc0f68719300997 upstream.

    When we see a jump also check that the offset gets us to beginning of
    a rule (an ipt_entry).

    The extra overhead is negible, even with absurd cases.

    300k custom rules, 300k jumps to 'next' user chain:
    [ plus one jump from INPUT to first userchain ]:

    Before:
    real 0m24.874s
    user 0m7.532s
    sys 0m16.076s

    After:
    real 0m27.464s
    user 0m7.436s
    sys 0m18.840s

    Signed-off-by: Florian Westphal <fw@strlen.de>
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
    [wt: pick the patch from 3.14, it slightly differs to address the issue
    described here : https://patchwork.ozlabs.org/patch/650121/]
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    ---
    net/ipv4/netfilter/arp_tables.c | 17 +++++++++++++++++
    net/ipv4/netfilter/ip_tables.c | 17 +++++++++++++++++
    net/ipv6/netfilter/ip6_tables.c | 17 +++++++++++++++++
    3 files changed, 51 insertions(+)

    diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
    index 7460b7b..473ec55 100644
    --- a/net/ipv4/netfilter/arp_tables.c
    +++ b/net/ipv4/netfilter/arp_tables.c
    @@ -358,6 +358,19 @@ static inline bool unconditional(const struct arpt_entry *e)
    memcmp(&e->arp, &uncond, sizeof(uncond)) == 0;
    }

    +static bool find_jump_target(const struct xt_table_info *t,
    + const void *entry0,
    + const struct arpt_entry *target)
    +{
    + struct arpt_entry *iter;
    +
    + xt_entry_foreach(iter, entry0, t->size) {
    + if (iter == target)
    + return true;
    + }
    + return false;
    +}
    +
    /* Figures out from what hook each rule can be called: returns 0 if
    * there are loops. Puts hook bitmask in comefrom.
    */
    @@ -451,6 +464,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
    /* This a jump; chase it. */
    duprintf("Jump rule %u -> %u\n",
    pos, newpos);
    + e = (struct arpt_entry *)
    + (entry0 + newpos);
    + if (!find_jump_target(newinfo, entry0, e))
    + return 0;
    } else {
    /* ... this is a fallthru */
    newpos = pos + e->next_offset;
    diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
    index 8fc22ee..dba9d80 100644
    --- a/net/ipv4/netfilter/ip_tables.c
    +++ b/net/ipv4/netfilter/ip_tables.c
    @@ -434,6 +434,19 @@ ipt_do_table(struct sk_buff *skb,
    #endif
    }

    +static bool find_jump_target(const struct xt_table_info *t,
    + const void *entry0,
    + const struct ipt_entry *target)
    +{
    + struct ipt_entry *iter;
    +
    + xt_entry_foreach(iter, entry0, t->size) {
    + if (iter == target)
    + return true;
    + }
    + return false;
    +}
    +
    /* Figures out from what hook each rule can be called: returns 0 if
    there are loops. Puts hook bitmask in comefrom. */
    static int
    @@ -531,6 +544,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
    /* This a jump; chase it. */
    duprintf("Jump rule %u -> %u\n",
    pos, newpos);
    + e = (struct ipt_entry *)
    + (entry0 + newpos);
    + if (!find_jump_target(newinfo, entry0, e))
    + return 0;
    } else {
    /* ... this is a fallthru */
    newpos = pos + e->next_offset;
    diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
    index 63f7876..97a8d25 100644
    --- a/net/ipv6/netfilter/ip6_tables.c
    +++ b/net/ipv6/netfilter/ip6_tables.c
    @@ -444,6 +444,19 @@ ip6t_do_table(struct sk_buff *skb,
    #endif
    }

    +static bool find_jump_target(const struct xt_table_info *t,
    + const void *entry0,
    + const struct ip6t_entry *target)
    +{
    + struct ip6t_entry *iter;
    +
    + xt_entry_foreach(iter, entry0, t->size) {
    + if (iter == target)
    + return true;
    + }
    + return false;
    +}
    +
    /* Figures out from what hook each rule can be called: returns 0 if
    there are loops. Puts hook bitmask in comefrom. */
    static int
    @@ -541,6 +554,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
    /* This a jump; chase it. */
    duprintf("Jump rule %u -> %u\n",
    pos, newpos);
    + e = (struct ip6t_entry *)
    + (entry0 + newpos);
    + if (!find_jump_target(newinfo, entry0, e))
    + return 0;
    } else {
    /* ... this is a fallthru */
    newpos = pos + e->next_offset;
    --
    2.8.0.rc2.1.gbe9624a
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