On Thu, Jul 28, 2022 at 08:00:00PM -0400, Abhishek Shah wrote:
> Dear Herbert,
>
> Thanks for your quick reply and sorry for not being more clear about the
> inconsistencies. We identified security implications when algorithms
> disappear or reappear during the execution of *compose_sadb_supported*.
>
> In more detail,
>
> 1) If after *xfrm_count_pfkey_auth_supported* has finished counting the
> available algos, a secondary thread changes the availability of an algo
> through *xfrm_probe_algs*, it will return an incorrect number of available
> algorithms. If an algo was added during the racing access, the code
> allocates a buffer that is smaller than the number of available algorithms
> at net/key/af_key.c#L1619
> <https://elixir.bootlin.com/linux/v5.18-rc5/source/net/key/af_key.c#L1619>.
> This will result in an out of bounds write when the buffer is later
> populated at net/key/af_key.c#L1657
> <https://elixir.bootlin.com/linux/v5.18-rc5/source/net/key/af_key.c#L1657>.
OK this is a real bug caused by this commit:
commit 283bc9f35bbbcb0e9ab4e6d2427da7f9f710d52d
Author: Fan Du <[email protected]>
Date: Thu Nov 7 17:47:50 2013 +0800
xfrm: Namespacify xfrm state/policy locks
It neglected to convert xfrm_probe_algs to namespaces so the
previous assumption of exclusive ownership of xfrm_algo_list
by the current afkey request is no longer true.
Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
When namespace support was added to xfrm/afkey, it caused the
previously single-threaded call to xfrm_probe_algs to become
multi-threaded. This is buggy and needs to be fixed with a mutex.
Reported-by: Abhishek Shah <[email protected]>
Fixes: 283bc9f35bbb ("xfrm: Namespacify xfrm state/policy locks")
Signed-off-by: Herbert Xu <[email protected]>
diff --git a/net/key/af_key.c b/net/key/af_key.c
index fb16d7c4e1b8..20e73643b9c8 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -1697,9 +1697,12 @@ static int pfkey_register(struct sock *sk, struct sk_buff *skb, const struct sad
pfk->registered |= (1<<hdr->sadb_msg_satype);
}
+ mutex_lock(&pfkey_mutex);
xfrm_probe_algs();
supp_skb = compose_sadb_supported(hdr, GFP_KERNEL | __GFP_ZERO);
+ mutex_unlock(&pfkey_mutex);
+
if (!supp_skb) {
if (hdr->sadb_msg_satype != SADB_SATYPE_UNSPEC)
pfk->registered &= ~(1<<hdr->sadb_msg_satype);
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Thu, Aug 04, 2022 at 06:03:46PM +0800, Herbert Xu wrote:
> When namespace support was added to xfrm/afkey, it caused the
> previously single-threaded call to xfrm_probe_algs to become
> multi-threaded. This is buggy and needs to be fixed with a mutex.
>
> Reported-by: Abhishek Shah <[email protected]>
> Fixes: 283bc9f35bbb ("xfrm: Namespacify xfrm state/policy locks")
> Signed-off-by: Herbert Xu <[email protected]>
Applied, thanks a lot Herbert!
We can confirm we tested this patch and it prevents the race we
detected in xfrm_ealg_get_byname / xfrm_probe_algs.
Best,
Gabe
On Thu, Aug 4, 2022 at 6:03 AM Herbert Xu <[email protected]> wrote:
>
> When namespace support was added to xfrm/afkey, it caused the
> previously single-threaded call to xfrm_probe_algs to become
> multi-threaded. This is buggy and needs to be fixed with a mutex.
>
> Reported-by: Abhishek Shah <[email protected]>
> Fixes: 283bc9f35bbb ("xfrm: Namespacify xfrm state/policy locks")
> Signed-off-by: Herbert Xu <[email protected]>
>
> diff --git a/net/key/af_key.c b/net/key/af_key.c
> index fb16d7c4e1b8..20e73643b9c8 100644
> --- a/net/key/af_key.c
> +++ b/net/key/af_key.c
> @@ -1697,9 +1697,12 @@ static int pfkey_register(struct sock *sk, struct sk_buff *skb, const struct sad
> pfk->registered |= (1<<hdr->sadb_msg_satype);
> }
>
> + mutex_lock(&pfkey_mutex);
> xfrm_probe_algs();
>
> supp_skb = compose_sadb_supported(hdr, GFP_KERNEL | __GFP_ZERO);
> + mutex_unlock(&pfkey_mutex);
> +
> if (!supp_skb) {
> if (hdr->sadb_msg_satype != SADB_SATYPE_UNSPEC)
> pfk->registered &= ~(1<<hdr->sadb_msg_satype);
> --
> Email: Herbert Xu <[email protected]>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
Gabriel Ryan
PhD Candidate at Columbia University
cs.columbia.edu/~gabe