[PATCH] xfrm: Zero padding when dumping algos and encap

[Herbert Xu <herbert@gondor.apana.org.au>]

On Wed, Feb 08, 2023 at 12:54:34AM -0800, Hyunwoo Kim wrote:
> On Tue, Feb 07, 2023 at 02:04:43PM +0800, Herbert Xu wrote:
> > On Sat, Feb 04, 2023 at 09:50:18AM -0800, Hyunwoo Kim wrote:
> > > Since x->calg etc. are allocated with kmalloc, information
> > > in kernel heap can be leaked using netlink socket on
> > > systems without CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
> > > 
> Reported-by: syzbot+fa5414772d5c445dac3c@syzkaller.appspotmail.com

Thanks.  This line should go into the patch description.

However, I don't think your patch is sufficient as xfrm_user
does the same thing as af_key.

I think a better approach would be to not copy out past the
end of string in copy_to_user_state_extra.  Something like
this:

---8<---
When copying data to user-space we should ensure that only valid
data is copied over.  Padding in structures may be filled with
random (possibly sensitve) data and should never be given directly
to user-space.

This patch fixes the copying of xfrm algorithms and the encap
template in xfrm_user so that padding is zeroed.

Reported-by: syzbot+fa5414772d5c445dac3c@syzkaller.appspotmail.com
Reported-by: Hyunwoo Kim <v4bel@theori.io>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index cf5172d4ce68..b5d50ae89840 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1012,7 +1012,9 @@ static int copy_to_user_aead(struct xfrm_algo_aead *aead, struct sk_buff *skb)
 		return -EMSGSIZE;
 
 	ap = nla_data(nla);
-	memcpy(ap, aead, sizeof(*aead));
+	strscpy_pad(ap->alg_name, aead->alg_name, sizeof(ap->alg_name));
+	ap->alg_key_len = aead->alg_key_len;
+	ap->alg_icv_len = aead->alg_icv_len;
 
 	if (redact_secret && aead->alg_key_len)
 		memset(ap->alg_key, 0, (aead->alg_key_len + 7) / 8);
@@ -1032,7 +1034,8 @@ static int copy_to_user_ealg(struct xfrm_algo *ealg, struct sk_buff *skb)
 		return -EMSGSIZE;
 
 	ap = nla_data(nla);
-	memcpy(ap, ealg, sizeof(*ealg));
+	strscpy_pad(ap->alg_name, ealg->alg_name, sizeof(ap->alg_name));
+	ap->alg_key_len = ealg->alg_key_len;
 
 	if (redact_secret && ealg->alg_key_len)
 		memset(ap->alg_key, 0, (ealg->alg_key_len + 7) / 8);
@@ -1043,6 +1046,40 @@ static int copy_to_user_ealg(struct xfrm_algo *ealg, struct sk_buff *skb)
 	return 0;
 }
 
+static int copy_to_user_calg(struct xfrm_algo *calg, struct sk_buff *skb)
+{
+	struct nlattr *nla = nla_reserve(skb, XFRMA_ALG_COMP, sizeof(*calg));
+	struct xfrm_algo *ap;
+
+	if (!nla)
+		return -EMSGSIZE;
+
+	ap = nla_data(nla);
+	strscpy_pad(ap->alg_name, calg->alg_name, sizeof(ap->alg_name));
+	ap->alg_key_len = 0;
+
+	return 0;
+}
+
+static int copy_to_user_encap(struct xfrm_encap_tmpl *ep, struct sk_buff *skb)
+{
+	struct nlattr *nla = nla_reserve(skb, XFRMA_ALG_COMP, sizeof(*ep));
+	struct xfrm_encap_tmpl *uep;
+
+	if (!nla)
+		return -EMSGSIZE;
+
+	uep = nla_data(nla);
+	memset(uep, 0, sizeof(*uep));
+
+	uep->encap_type = ep->encap_type;
+	uep->encap_sport = ep->encap_sport;
+	uep->encap_dport = ep->encap_dport;
+	uep->encap_oa = ep->encap_oa;
+
+	return 0;
+}
+
 static int xfrm_smark_put(struct sk_buff *skb, struct xfrm_mark *m)
 {
 	int ret = 0;
@@ -1098,12 +1135,12 @@ static int copy_to_user_state_extra(struct xfrm_state *x,
 			goto out;
 	}
 	if (x->calg) {
-		ret = nla_put(skb, XFRMA_ALG_COMP, sizeof(*(x->calg)), x->calg);
+		ret = copy_to_user_calg(x->calg, skb);
 		if (ret)
 			goto out;
 	}
 	if (x->encap) {
-		ret = nla_put(skb, XFRMA_ENCAP, sizeof(*x->encap), x->encap);
+		ret = copy_to_user_encap(x->encap, skb);
 		if (ret)
 			goto out;
 	}
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt