6.12-stable review patch. If anyone has any objections, please let me know.
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From: Ido Schimmel idosch@nvidia.com
[ Upstream commit 390b3a300d7872cef9588f003b204398be69ce08 ]
The kernel forbids the creation of non-FDB nexthop groups with FDB nexthops:
# ip nexthop add id 1 via 192.0.2.1 fdb # ip nexthop add id 2 group 1 Error: Non FDB nexthop group cannot have fdb nexthops.
And vice versa:
# ip nexthop add id 3 via 192.0.2.2 dev dummy1 # ip nexthop add id 4 group 3 fdb Error: FDB nexthop group can only have fdb nexthops.
However, as long as no routes are pointing to a non-FDB nexthop group, the kernel allows changing the type of a nexthop from FDB to non-FDB and vice versa:
# ip nexthop add id 5 via 192.0.2.2 dev dummy1 # ip nexthop add id 6 group 5 # ip nexthop replace id 5 via 192.0.2.2 fdb # echo $? 0
This configuration is invalid and can result in a NPD [1] since FDB nexthops are not associated with a nexthop device:
# ip route add 198.51.100.1/32 nhid 6 # ping 198.51.100.1
Fix by preventing nexthop FDB status change while the nexthop is in a group:
# ip nexthop add id 7 via 192.0.2.2 dev dummy1 # ip nexthop add id 8 group 7 # ip nexthop replace id 7 via 192.0.2.2 fdb Error: Cannot change nexthop FDB status while in a group.
[1] BUG: kernel NULL pointer dereference, address: 00000000000003c0 [...] Oops: Oops: 0000 [#1] SMP CPU: 6 UID: 0 PID: 367 Comm: ping Not tainted 6.17.0-rc6-virtme-gb65678cacc03 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 RIP: 0010:fib_lookup_good_nhc+0x1e/0x80 [...] Call Trace: <TASK> fib_table_lookup+0x541/0x650 ip_route_output_key_hash_rcu+0x2ea/0x970 ip_route_output_key_hash+0x55/0x80 __ip4_datagram_connect+0x250/0x330 udp_connect+0x2b/0x60 __sys_connect+0x9c/0xd0 __x64_sys_connect+0x18/0x20 do_syscall_64+0xa4/0x2a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53
Fixes: 38428d68719c ("nexthop: support for fdb ecmp nexthops") Reported-by: syzbot+6596516dd2b635ba2350@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68c9a4d2.050a0220.3c6139.0e63.GAE@google.com/ Tested-by: syzbot+6596516dd2b635ba2350@syzkaller.appspotmail.com Signed-off-by: Ido Schimmel idosch@nvidia.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://patch.msgid.link/20250921150824.149157-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/nexthop.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index 93aaea0006ba7..c52ff9364ae8d 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2375,6 +2375,13 @@ static int replace_nexthop_single(struct net *net, struct nexthop *old, return -EINVAL; }
+ if (!list_empty(&old->grp_list) && + rtnl_dereference(new->nh_info)->fdb_nh != + rtnl_dereference(old->nh_info)->fdb_nh) { + NL_SET_ERR_MSG(extack, "Cannot change nexthop FDB status while in a group"); + return -EINVAL; + } + err = call_nexthop_notifiers(net, NEXTHOP_EVENT_REPLACE, new, extack); if (err) return err;