[RFC PATCH net-next] rtnetlink: add RTNH_F_REJECT_MASK

[Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>]

Introduce RTNH_F_REJECT_MASK mask which contains
all rtnh_flags which can't be set by the userspace
directly.

This mask will be used in the iproute utility
to exclude rtnh_flags which can't be restored
from "ip route save" image.

This patch doesn't change kernel behavior, but
it looks like we need to prohibit setting
RTNH_F_OFFLOAD, RTNH_F_TRAP flags too.
Am I right?

Please, take a look on
[RFC PATCH iproute2] ip route: save: exclude rtnh_flags which can't be set

Cc: David Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Ido Schimmel <idosch@nvidia.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>
Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
---
 include/uapi/linux/rtnetlink.h | 3 +++
 net/ipv4/fib_semantics.c       | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 5888492a5257..c15e591e5d25 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_F_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..7a383c54fe46 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_F_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_F_REJECT_MASK) {
 		NL_SET_ERR_MSG(extack,
 			       "Invalid rtm_flags - can not contain DEAD or LINKDOWN");
 		goto err_inval;
-- 
2.31.1