Tools such as vpnc try to flush routes when run inside network namespaces by writing 1 into /proc/sys/net/ipv4/route/flush. This currently does not work because flush is not enabled in non-initial network namespaces. Since routes are per network namespace it is safe to enable /proc/sys/net/ipv4/route/flush in there.
Link: https://github.com/lxc/lxd/issues/4257 Signed-off-by: Christian Brauner <christian.brau...@ubuntu.com> --- net/ipv4/route.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 6cb7cff22db9..41726e26cd5f 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -3197,9 +3197,11 @@ static struct ctl_table ipv4_route_table[] = { { } }; +static const char ipv4_route_flush_procname[] = "flush"; + static struct ctl_table ipv4_route_flush_table[] = { { - .procname = "flush", + .procname = ipv4_route_flush_procname, .maxlen = sizeof(int), .mode = 0200, .proc_handler = ipv4_sysctl_rtcache_flush, @@ -3217,9 +3219,11 @@ static __net_init int sysctl_route_net_init(struct net *net) if (!tbl) goto err_dup; - /* Don't export sysctls to unprivileged users */ - if (net->user_ns != &init_user_ns) - tbl[0].procname = NULL; + /* Don't export non-whitelisted sysctls to unprivileged users */ + if (net->user_ns != &init_user_ns) { + if (tbl[0].procname != ipv4_route_flush_procname) + tbl[0].procname = NULL; + } } tbl[0].extra1 = net; -- 2.22.0
