netfilter: x_tables: don't move to non-existent next rule

Ben Hawkes says:

 In the mark_source_chains function (net/ipv4/netfilter/ip_tables.c) it
 is possible for a user-supplied ipt_entry structure to have a large
 next_offset field. This field is not bounds checked prior to writing a
 counter value at the supplied offset.

Base chains enforce absolute verdict.

User defined chains are supposed to end with an unconditional return,
xtables userspace adds them automatically.

But if such return is missing we will move to non-existent next rule.

Reported-by: Ben Hawkes <hawkes@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 13 insertions, 3 deletions

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 4133b0f513af..82a434bf8653 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -439,6 +439,8 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
                                 size = e->next_offset;
                                 e = (struct arpt_entry *)
                                         (entry0 + pos + size);
+                                if (pos + size >= newinfo->size)
+                                        return 0;
                                 e->counters.pcnt = pos;
                                 pos += size;
                         } else {
@@ -461,6 +463,8 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
                                 } else {
                                         /* ... this is a fallthru */
                                         newpos = pos + e->next_offset;
+                                        if (newpos >= newinfo->size)
+                                                return 0;
                                 }
                                 e = (struct arpt_entry *)
                                         (entry0 + newpos);
@@ -691,10 +695,8 @@ static int translate_table(struct xt_table_info *newinfo, void *entry0,
                 }
         }
 
-        if (!mark_source_chains(newinfo, repl->valid_hooks, entry0)) {
-                duprintf("Looping hook\n");
+        if (!mark_source_chains(newinfo, repl->valid_hooks, entry0))
                 return -ELOOP;
-        }
 
         /* Finally, each sanity check must pass */
         i = 0;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 631c100a1338..e301a3db4717 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -520,6 +520,8 @@ mark_source_chains(const struct xt_table_info *newinfo,
                                 size = e->next_offset;
                                 e = (struct ipt_entry *)
                                         (entry0 + pos + size);
+                                if (pos + size >= newinfo->size)
+                                        return 0;
                                 e->counters.pcnt = pos;
                                 pos += size;
                         } else {
@@ -541,6 +543,8 @@ mark_source_chains(const struct xt_table_info *newinfo,
                                 } else {
                                         /* ... this is a fallthru */
                                         newpos = pos + e->next_offset;
+                                        if (newpos >= newinfo->size)
+                                                return 0;
                                 }
                                 e = (struct ipt_entry *)
                                         (entry0 + newpos);
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 86b67b70b626..7b3335bce3fd 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -532,6 +532,8 @@ mark_source_chains(const struct xt_table_info *newinfo,
                                 size = e->next_offset;
                                 e = (struct ip6t_entry *)
                                         (entry0 + pos + size);
+                                if (pos + size >= newinfo->size)
+                                        return 0;
                                 e->counters.pcnt = pos;
                                 pos += size;
                         } else {
@@ -553,6 +555,8 @@ mark_source_chains(const struct xt_table_info *newinfo,
                                 } else {
                                         /* ... this is a fallthru */
                                         newpos = pos + e->next_offset;
+                                        if (newpos >= newinfo->size)
+                                                return 0;
                                 }
                                 e = (struct ip6t_entry *)
                                         (entry0 + newpos);