Re: [PATCH nf] netfilter: ebtables: CONFIG_COMPAT: don't trust userland offsets

[Pablo Neira Ayuso]

On Mon, Feb 19, 2018 at 01:24:15AM +0100, Florian Westphal wrote:
> We need to make sure the offsets are not out of range of the
> total size.
> Also check that they are in ascending order.
> 
> The WARN_ON triggered by syzkaller (it sets panic_on_warn) is
> changed to also bail out, no point in continuing parsing.
> 
> Briefly tested with simple ruleset of
> -A INPUT --limit 1/s' --log
> plus jump to custom chains using 32bit ebtables binary.

Also applied, thanks.

[PATCH nf] netfilter: ebtables: CONFIG_COMPAT: don't trust userland offsets

[Florian Westphal]

We need to make sure the offsets are not out of range of the
total size.
Also check that they are in ascending order.

The WARN_ON triggered by syzkaller (it sets panic_on_warn) is
changed to also bail out, no point in continuing parsing.

Briefly tested with simple ruleset of
-A INPUT --limit 1/s' --log
plus jump to custom chains using 32bit ebtables binary.

Reported-by: 
Signed-off-by: Florian Westphal 
---
 net/bridge/netfilter/ebtables.c | 13 -
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 02c4b409d317..3f536c7a3354 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2053,7 +2053,9 @@ static int ebt_size_mwt(struct compat_ebt_entry_mwt 
*match32,
if (match_kern)
match_kern->match_size = ret;
 
-   WARN_ON(type == EBT_COMPAT_TARGET && size_left);
+   if (WARN_ON(type == EBT_COMPAT_TARGET && size_left))
+   return -EINVAL;
+
match32 = (struct compat_ebt_entry_mwt *) buf;
}
 
@@ -2109,6 +2111,15 @@ static int size_entry_mwt(struct ebt_entry *entry, const 
unsigned char *base,
 *
 * offsets are relative to beginning of struct ebt_entry (i.e., 0).
 */
+   for (i = 0; i < 4 ; ++i) {
+   if (offsets[i] >= *total)
+   return -EINVAL;
+   if (i == 0)
+   continue;
+   if (offsets[i-1] > offsets[i])
+   return -EINVAL;
+   }
+
for (i = 0, j = 1 ; j < 4 ; j++, i++) {
struct compat_ebt_entry_mwt *match32;
unsigned int size;
-- 
2.16.1