Re: net/key: slab-out-of-bounds in pfkey_compile_policy

From: Steffen Klassert
Date: Fri May 05 2017 - 05:11:12 EST

On Tue, May 02, 2017 at 06:45:03PM +0200, Andrey Konovalov wrote:
> Hi,
> I've got the following error report while fuzzing the kernel with syzkaller.
> On commit d3b5d35290d729a2518af00feca867385a1b08fa (4.11).
> A reproducer and .config are attached.
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in pfkey_compile_policy+0x8e6/0xd40 at
> addr ffff88006701f798
> Read of size 1280 by task a.out/4181

This bug was introduced twelve years ago...

This patch is based just on code review, I don't have an option to
function test this. But I see that we now exit with -EINVAL before the
memcpy that causes the slab-out-of-bounds when using your reproducer,
so it should at least fix the bug.

Subject: [PATCH RFC] af_key: Fix slab-out-of-bounds in pfkey_compile_policy.

The sadb_x_sec_len is stored in the unit 'byte divided by eight'.
So we have to multiply this value by eight before we can do
size checks. Otherwise we may get a slab-out-of-bounds when
we memcpy the user sec_ctx.

Fixes: df71837d502 ("[LSM-IPSec]: Security association restriction.")
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
net/key/af_key.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/key/af_key.c b/net/key/af_key.c
index c1950bb..512dc43 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -3285,7 +3285,7 @@ static struct xfrm_policy *pfkey_compile_policy(struct sock *sk, int opt,
p += pol->sadb_x_policy_len*8;
sec_ctx = (struct sadb_x_sec_ctx *)p;
if (len < pol->sadb_x_policy_len*8 +
- sec_ctx->sadb_x_sec_len) {
+ sec_ctx->sadb_x_sec_len*8) {
*dir = -EINVAL;
goto out;