From: Jiayuan Chen <[email protected]>
When a standalone IPv6 nexthop object is created with a loopback device
(e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies
it as a reject route. This is because nexthop objects have no destination
prefix (fc_dst=::), causing fib6_is_reject() to match any loopback
nexthop. The reject path skips fib_nh_common_init(), leaving
nhc_pcpu_rth_output unallocated. If an IPv4 route later references this
nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and
panics.
Simplify the check in fib6_nh_init() to only match explicit reject
routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback
promotion heuristic in fib6_is_reject() is handled separately by
ip6_route_info_create_nh(). After this change, the three cases behave
as follows:
1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"):
RTF_REJECT is set, enters reject path, skips fib_nh_common_init().
No behavior change.
2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"):
RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
called. ip6_route_info_create_nh() still promotes it to reject
afterward. nhc_pcpu_rth_output is allocated but unused, which is
harmless.
3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"):
RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
called. nhc_pcpu_rth_output is properly allocated, fixing the crash
when IPv4 routes reference this nexthop.
Suggested-by: Ido Schimmel <[email protected]>
Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects")
Reported-by: [email protected]
Closes:
https://lore.kernel.org/all/[email protected]/T/
Signed-off-by: Jiayuan Chen <[email protected]>
---
net/ipv6/route.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index c0350d97307e..08b4a324987e 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3582,7 +3582,6 @@ int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh,
netdevice_tracker *dev_tracker = &fib6_nh->fib_nh_dev_tracker;
struct net_device *dev = NULL;
struct inet6_dev *idev = NULL;
- int addr_type;
int err;
fib6_nh->fib_nh_family = AF_INET6;
@@ -3624,11 +3623,10 @@ int fib6_nh_init(struct net *net, struct fib6_nh
*fib6_nh,
fib6_nh->fib_nh_weight = 1;
- /* We cannot add true routes via loopback here,
- * they would result in kernel looping; promote them to reject routes
+ /* Reset the nexthop device to the loopback device in case of reject
+ * routes.
*/
- addr_type = ipv6_addr_type(&cfg->fc_dst);
- if (fib6_is_reject(cfg->fc_flags, dev, addr_type)) {
+ if (cfg->fc_flags & RTF_REJECT) {
/* hold loopback dev/idev if we haven't done so. */
if (dev != net->loopback_dev) {
if (dev) {
--
2.43.0
