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

On Tue, 30 Nov 2021 11:28:32 +0200
Ido Schimmel [off-list ref] wrote:

quoted

On Tue, Nov 30, 2021 at 11:35:17AM +0300, Alexander Mikhalitsyn wrote:

quoted

On Tue, 30 Nov 2021 09:59:25 +0200
Ido Schimmel [off-list ref] wrote:

quoted

Looking at the patch again, what is the motivation to expose
RTNH_REJECT_MASK to user space? iproute2 already knows that it only
makes sense to set RTNH_F_ONLINK. Can't we just do:

Sorry, but that's not fully clear for me, why we should exclude RTNH_F_ONLINK?
I thought that we should exclude RTNH_F_DEAD and RTNH_F_LINKDOWN just because
kernel doesn't allow to set these flags.

I don't think we should exclude RTNH_F_ONLINK. I'm saying that it is the
only flag that it makes sense to send to the kernel in the ancillary
header of RTM_NEWROUTE messages. The rest of the RNTH_F_* flags are
either not used by the kernel or are only meant to be sent from the
kernel to user space. Due to omission, they are mistakenly allowed.

Ah, okay, so, the patch should be like

diff --git a/ip/iproute.c b/ip/iproute.c
index 1447a5f78f49..0e6dad2b67e5 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c

@@ -1632,6 +1632,8 @@ static int save_route(struct nlmsghdr *n, void *arg)
        if (!filter_nlmsg(n, tb, host_len))
                return 0;
 
+       r->rtm_flags &= RTNH_F_ONLINK;
+
        ret = write(STDOUT_FILENO, n, n->nlmsg_len);
        if ((ret > 0) && (ret != n->nlmsg_len)) {
                fprintf(stderr, "Short write while saving nlmsg\n");

to filter out all flags *except* RTNH_F_ONLINK.