Re: [PATCH net-next] rtnetlink: add RTNH_REJECT_MASK

On 11/28/21 7:01 AM, Ido Schimmel wrote:

On Fri, Nov 26, 2021 at 04:43:11PM +0300, Alexander Mikhalitsyn wrote:

quoted

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 5888492a5257..9c065e2fdef9 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h

@@ -417,6 +417,9 @@ struct rtnexthop {
 #define RTNH_COMPARE_MASK	(RTNH_F_DEAD | RTNH_F_LINKDOWN | \
 				 RTNH_F_OFFLOAD | RTNH_F_TRAP)
 
+/* these flags can't be set by the userspace */
+#define RTNH_REJECT_MASK	(RTNH_F_DEAD | RTNH_F_LINKDOWN)
+
 /* Macros to handle hexthops */
 
 #define RTNH_ALIGNTO	4

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 4c0c33e4710d..805f5e05b56d 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -685,7 +685,7 @@ static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh,
 			return -EINVAL;
 		}
 
-		if (rtnh->rtnh_flags & (RTNH_F_DEAD | RTNH_F_LINKDOWN)) {
+		if (rtnh->rtnh_flags & RTNH_REJECT_MASK) {
 			NL_SET_ERR_MSG(extack,
 				       "Invalid flags for nexthop - can not contain DEAD or LINKDOWN");
 			return -EINVAL;

@@ -1363,7 +1363,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 		goto err_inval;
 	}
 
-	if (cfg->fc_flags & (RTNH_F_DEAD | RTNH_F_LINKDOWN)) {
+	if (cfg->fc_flags & RTNH_REJECT_MASK) {
 		NL_SET_ERR_MSG(extack,
 			       "Invalid rtm_flags - can not contain DEAD or LINKDOWN");

Instead of a deny list as in the legacy nexthop code, the new nexthop
code has an allow list (from rtm_to_nh_config()):

	if (nhm->nh_flags & ~NEXTHOP_VALID_USER_FLAGS) {
		NL_SET_ERR_MSG(extack, "Invalid nexthop flags in ancillary header");
		goto out;
	}

Where:

#define NEXTHOP_VALID_USER_FLAGS RTNH_F_ONLINK

So while the legacy nexthop code allows setting flags such as
RTNH_F_OFFLOAD, the new nexthop code denies them. I don't have a use
case for setting these flags from user space so I don't care if we allow
or deny them, but I believe the legacy and new nexthop code should be
consistent.

WDYT? Should we allow these flags in the new nexthop code as well or
keep denying them?

quoted

 		goto err_inval;

I like the positive naming - RTNH_VALID_USER_FLAGS.

nexthop API should allow the OFFLOAD flag to be consistent; separate
change though.