[PATCH ipsec] xfrm: Reject optional tunnel/BEET mode templates in outbound policies

From: Tobias Brunner <tobias@strongswan.org>
To: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	netdev@vger.kernel.org, "David S . Miller" <davem@davemloft.net>
Subject: [PATCH ipsec] xfrm: Reject optional tunnel/BEET mode templates in outbound policies
Date: Fri, 5 May 2023 12:16:16 +0200	[thread overview]
Message-ID: <5d5bf4d9-5b63-ae0d-2f65-770e911ea7d6@strongswan.org> (raw)
In-Reply-To: <ZEePE9LMA0pWxz9r@gondor.apana.org.au>

xfrm_state_find() uses `encap_family` of the current template with
the passed local and remote addresses to find a matching state.
If an optional tunnel or BEET mode template is skipped in a mixed-family
scenario, there could be a mismatch causing an out-of-bounds read as
the addresses were not replaced to match the family of the next template.

While there are theoretical use cases for optional templates in outbound
policies, the only practical one is to skip IPComp states in inbound
policies if uncompressed packets are received that are handled by an
implicitly created IPIP state instead.

Signed-off-by: Tobias Brunner <tobias@strongswan.org>
---
  net/xfrm/xfrm_user.c | 14 +++++++++-----
  1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index af8fbcbfbe69..6794b9dea27a 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1768,7 +1768,7 @@ static void copy_templates(struct xfrm_policy *xp, struct xfrm_user_tmpl *ut,
  }
  
  static int validate_tmpl(int nr, struct xfrm_user_tmpl *ut, u16 family,
-			 struct netlink_ext_ack *extack)
+			 int dir, struct netlink_ext_ack *extack)
  {
  	u16 prev_family;
  	int i;
@@ -1794,6 +1794,10 @@ static int validate_tmpl(int nr, struct xfrm_user_tmpl *ut, u16 family,
  		switch (ut[i].mode) {
  		case XFRM_MODE_TUNNEL:
  		case XFRM_MODE_BEET:
+			if (ut[i].optional && dir == XFRM_POLICY_OUT) {
+				NL_SET_ERR_MSG(extack, "Mode in optional template not allowed in outbound policy");
+				return -EINVAL;
+			}
  			break;
  		default:
  			if (ut[i].family != prev_family) {
@@ -1831,7 +1835,7 @@ static int validate_tmpl(int nr, struct xfrm_user_tmpl *ut, u16 family,
  }
  
  static int copy_from_user_tmpl(struct xfrm_policy *pol, struct nlattr **attrs,
-			       struct netlink_ext_ack *extack)
+			       int dir, struct netlink_ext_ack *extack)
  {
  	struct nlattr *rt = attrs[XFRMA_TMPL];
  
@@ -1842,7 +1846,7 @@ static int copy_from_user_tmpl(struct xfrm_policy *pol, struct nlattr **attrs,
  		int nr = nla_len(rt) / sizeof(*utmpl);
  		int err;
  
-		err = validate_tmpl(nr, utmpl, pol->family, extack);
+		err = validate_tmpl(nr, utmpl, pol->family, dir, extack);
  		if (err)
  			return err;
  
@@ -1919,7 +1923,7 @@ static struct xfrm_policy *xfrm_policy_construct(struct net *net,
  	if (err)
  		goto error;
  
-	if (!(err = copy_from_user_tmpl(xp, attrs, extack)))
+	if (!(err = copy_from_user_tmpl(xp, attrs, p->dir, extack)))
  		err = copy_from_user_sec_ctx(xp, attrs);
  	if (err)
  		goto error;
@@ -3498,7 +3502,7 @@ static struct xfrm_policy *xfrm_compile_policy(struct sock *sk, int opt,
  		return NULL;
  
  	nr = ((len - sizeof(*p)) / sizeof(*ut));
-	if (validate_tmpl(nr, ut, p->sel.family, NULL))
+	if (validate_tmpl(nr, ut, p->sel.family, p->dir, NULL))
  		return NULL;
  
  	if (p->dir > XFRM_POLICY_OUT)
-- 
2.34.1


