xfrm: validate new SA's prefixlen using SA family when sel.family is unset

This expands the validation introduced in commit 07bf790 ("xfrm:
Validate address prefix lengths in the xfrm selector.")

syzbot created an SA with
    usersa.sel.family = AF_UNSPEC
    usersa.sel.prefixlen_s = 128
    usersa.family = AF_INET

Because of the AF_UNSPEC selector, verify_newsa_info doesn't put
limits on prefixlen_{s,d}. But then copy_from_user_state sets
x->sel.family to usersa.family (AF_INET). Do the same conversion in
verify_newsa_info before validating prefixlen_{s,d}, since that's how
prefixlen is going to be used later on.

Reported-by: [email protected]
Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Sabrina Dubroca <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>

Author: qsn

net/xfrm/xfrm_user.c

@@ -201,6 +201,7 @@ static int verify_newsa_info(struct xfrm_usersa_info *p,
 {
 	int err;
 	u8 sa_dir = attrs[XFRMA_SA_DIR] ? nla_get_u8(attrs[XFRMA_SA_DIR]) : 0;
+	u16 family = p->sel.family;
 
 	err = -EINVAL;
 	switch (p->family) {
@@ -221,7 +222,10 @@ static int verify_newsa_info(struct xfrm_usersa_info *p,
 		goto out;
 	}
 
-	switch (p->sel.family) {
+	if (!family && !(p->flags & XFRM_STATE_AF_UNSPEC))
+		family = p->family;
+
+	switch (family) {
 	case AF_UNSPEC:
 		break;