kernel/linux.git/net/ipv6/route.c, branch linux-7.1.y

ipv6: fix possible infinite loop in fib6_select_path()

2026-05-29T19:41:00+00:00

Found while auditing the same pattern Sashiko reported in rt6_fill_node() [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings) without waiting for RCU readers; first->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &first->fib6_siblings as its terminator. fib6_purge_rt() always WRITE_ONCE()s first->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev Fixes: d9ccb18f83ea ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn") Signed-off-by: Jiayuan Chen Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260527053133.180695-2-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski

ipv6: fix possible infinite loop in rt6_fill_node()

2026-05-29T19:40:05+00:00

Sashiko reported this issue [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&rt->fib6_siblings) without waiting for RCU readers; rt->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &rt->fib6_siblings, causing a CPU stall. fib6_del_route() always WRITE_ONCE()s rt->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev Fixes: d9ccb18f83ea ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn") Signed-off-by: Jiayuan Chen Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260527053133.180695-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski

ipv6: route: Unregister netdevice notifier on BPF init failure

2026-05-21T14:43:15+00:00

ip6_route_init() registers ip6_route_dev_notifier before registering the IPv6 route BPF iterator target. If bpf_iter_register() fails after the notifier has been registered, the error path currently jumps to out_register_late_subsys and unwinds the RTNL handlers and pernet route state without removing the notifier from the netdevice notifier chain. This leaves ip6_route_dev_notify() callable after the IPv6 route state it uses has been torn down. Add a separate unwind label for the BPF iterator failure path and unregister the netdevice notifier before continuing with the existing cleanup. Fixes: 138d0be35b14 ("net: bpf: Add netlink and ipv6_route bpf_iter targets") Signed-off-by: Yuho Choi Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260520030329.1061183-1-dbgh9129@gmail.com Signed-off-by: Jakub Kicinski

ipv6: Fix null-ptr-deref in fib6_mtu().

2026-05-06T00:32:57+00:00

syzbot reported null-ptr-deref in fib6_mtu(). [0] When res->f6i->fib6_pmtu is 0 in fib6_mtu(), it fetches MTU from __in6_dev_get(nh->fib_nh_dev)->cnf.mtu6. However, __in6_dev_get() could return NULL when the device is being unregistered. Let's return 0 MTU if __in6_dev_get() returns NULL in fib6_mtu(). [0]: Oops: general protection fault, probably for non-canonical address 0xdffffc00000000bc: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x00000000000005e0-0x00000000000005e7] CPU: 0 UID: 0 PID: 7890 Comm: syz.2.502 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:fib6_mtu net/ipv6/route.c:1648 [inline] RIP: 0010:rt6_insert_exception+0x9eb/0x10a0 net/ipv6/route.c:1753 Code: 3b 14 cf f7 45 85 f6 0f 85 1d 02 00 00 e8 7d 19 cf f7 48 8d bb e0 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 89 RSP: 0000:ffffc9000610f120 EFLAGS: 00010202 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc9000c001000 RDX: 00000000000000bc RSI: ffffffff8a38bc83 RDI: 00000000000005e0 RBP: ffff888052f06000 R08: 0000000000000005 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: ffff888042d16c00 R13: ffff888042d16cc8 R14: 0000000000000001 R15: 0000000000000500 FS: 0000000000000000(0000) GS:ffff88809717d000(0063) knlGS:00000000f540db40 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 00000000f73c6d50 CR3: 000000006eff0000 CR4: 0000000000352ef0 Call Trace: __ip6_rt_update_pmtu+0x555/0xd60 net/ipv6/route.c:2982 ip6_update_pmtu+0x34f/0x3b0 net/ipv6/route.c:3014 icmpv6_err+0x2a2/0x3f0 net/ipv6/icmp.c:82 icmpv6_notify+0x35e/0x820 net/ipv6/icmp.c:1087 icmpv6_rcv+0x10bf/0x1ae0 net/ipv6/icmp.c:1228 ip6_protocol_deliver_rcu+0xf97/0x1500 net/ipv6/ip6_input.c:478 ip6_input_finish+0x1e4/0x4a0 net/ipv6/ip6_input.c:529 NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] ip6_input+0x105/0x2f0 net/ipv6/ip6_input.c:540 ip6_mc_input+0x513/0xf50 net/ipv6/ip6_input.c:630 dst_input include/net/dst.h:480 [inline] ip6_rcv_finish net/ipv6/ip6_input.c:119 [inline] NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] ipv6_rcv+0x34c/0x3d0 net/ipv6/ip6_input.c:351 __netif_receive_skb_one_core+0x12d/0x1e0 net/core/dev.c:6202 __netif_receive_skb+0x1f/0x120 net/core/dev.c:6315 netif_receive_skb_internal net/core/dev.c:6401 [inline] netif_receive_skb+0x13b/0x7f0 net/core/dev.c:6460 tun_rx_batched.isra.0+0x3f6/0x750 drivers/net/tun.c:1511 tun_get_user+0x1e31/0x3c20 drivers/net/tun.c:1955 tun_chr_write_iter+0xdc/0x200 drivers/net/tun.c:2001 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6ac/0x1070 fs/read_write.c:688 ksys_write+0x12a/0x250 fs/read_write.c:740 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] do_int80_emulation+0x141/0x700 arch/x86/entry/syscall_32.c:172 asm_int80_emulation+0x1a/0x20 arch/x86/include/asm/idtentry.h:621 RIP: 0023:0xf715616b Code: 57 56 53 8b 44 24 14 f6 00 08 75 23 8b 44 24 18 8b 5c 24 1c 8b 4c 24 20 8b 54 24 24 8b 74 24 28 8b 7c 24 2c 8b 6c 24 30 cd 80 <5b> 5e 5f 5d c3 5b 5e 5f 5d e9 f7 a1 ff ff 66 90 66 90 66 90 90 53 RSP: 002b:00000000f540d44c EFLAGS: 00000246 ORIG_RAX: 0000000000000004 RAX: ffffffffffffffda RBX: 00000000000000c8 RCX: 0000000080000640 RDX: 000000000000007a RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 Fixes: dcd1f572954f ("net/ipv6: Remove fib6_idev") Reported-by: syzbot+01f005f9c6387ca6f6dd@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69f83f22.170a0220.13cc2.0004.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260504064316.3820775-1-kuniyu@google.com Signed-off-by: Jakub Kicinski

ipv6: update route serial number on NETDEV_CHANGE

2026-05-02T00:58:44+00:00

When using IPv6 ECMP routes, if a netdev listed as a nexthop experiences a carrier change event (e.g., a bond device generating a NETDEV_CHANGE event after its slaves go linkdown), established connections utilizing that nexthop fail to fail over to other available nexthops. Instead, these connections stall or drop. This happens because the IPv6 FIB code does not invalidate the socket's cached destination when a NETDEV_CHANGE event occurs. While fib6_ifdown() correctly marks the nexthop with RTNH_F_LINKDOWN, it leaves the route's serial number unchanged. As a result, sockets with a previously cached dst do not realize the route is no longer viable and continue to try using the non-functional nexthop. This behavior contrasts with IPv4, which actively flushes cached destinations on a NETDEV_CHANGE event (see fib_netdev_event() in net/ipv4/fib_frontend.c). Fix this by updating the route serial number in fib6_ifdown() when setting RTNH_F_LINKDOWN. This invalidates stale cached destinations, forcing sockets to perform a new route lookup and fail over to a functioning nexthop. Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)") Signed-off-by: Sagarika Sharma Reviewed-by: Kuniyuki Iwashima Reviewed-by: Ido Schimmel Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260430200909.527827-2-sharmasagarika@google.com Signed-off-by: Jakub Kicinski

ipv6: prepare headers for ipv6_stub removal

2026-03-29T18:21:23+00:00

In preparation for dropping ipv6_stub and converting its users to direct function calls, introduce static inline dummy functions and fallback macros in the IPv6 networking headers. In addition, introduce checks on fib6_nh_init(), ip6_dst_lookup_flow() and ip6_fragment() to avoid a crash due to ipv6.disable=1 set during booting. The other functions are safe as they cannot be called with ipv6.disable=1 set. These fallbacks ensure that when CONFIG_IPV6 is completely disabled, there are no compiling or linking errors due to code paths not guarded by preprocessor macro IS_ENABLED(CONFIG_IPV6). In addition, export ndisc_send_na(), ip6_route_input() and ip6_fragment(). Signed-off-by: Fernando Fernandez Mancera Tested-by: Ricardo B. Marlière Link: https://patch.msgid.link/20260325120928.15848-6-fmancera@suse.de Signed-off-by: Jakub Kicinski

ipv6: replace IS_BUILTIN(CONFIG_IPV6) with IS_ENABLED(CONFIG_IPV6)

2026-03-29T18:21:23+00:00

As IPv6 is built-in only, it does not make sense to continue using IS_BUILTIN(CONFIG_IPV6). Therefore, replace it with IS_ENABLED() when necessary and drop it if it isn't valid anymore. Notice that there is still one instance related to ICMPv6, as it requires more changes it will be handle separately. Signed-off-by: Fernando Fernandez Mancera Tested-by: Ricardo B. Marlière Acked-by: Martin KaFai Lau Link: https://patch.msgid.link/20260325120928.15848-4-fmancera@suse.de Signed-off-by: Jakub Kicinski

ipv6: Don't remove permanent routes with exceptions from tb6_gc_hlist.

2026-03-23T23:59:31+00:00

The cited commit mechanically put fib6_remove_gc_list() just after every fib6_clean_expires() call. When a temporary route is promoted to a permanent route, there may already be exception routes tied to it. If fib6_remove_gc_list() removes the route from tb6_gc_hlist, such exception routes will no longer be aged. Let's replace fib6_remove_gc_list() with a new helper fib6_may_remove_gc_list() and use fib6_age_exceptions() there. Note that net->ipv6 is only compiled when CONFIG_IPV6 is enabled, so fib6_{add,remove,may_remove}_gc_list() are guarded. Fixes: 5eb902b8e719 ("net/ipv6: Remove expired routes with a separated list of routes.") Signed-off-by: Kuniyuki Iwashima Reviewed-by: David Ahern Link: https://patch.msgid.link/20260320072317.2561779-3-kuniyu@google.com Signed-off-by: Jakub Kicinski

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

2026-03-05T15:53:17+00:00

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 Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects") Reported-by: syzbot+334190e097a98a1b81bb@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/698f8482.a70a0220.2c38d7.00ca.GAE@google.com/T/ Signed-off-by: Jiayuan Chen Reviewed-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/20260304113817.294966-2-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski

ipv6: fix NULL pointer deref in ip6_rt_get_dev_rcu()

2026-03-04T01:14:48+00:00

l3mdev_master_dev_rcu() can return NULL when the slave device is being un-slaved from a VRF. All other callers deal with this, but we lost the fallback to loopback in ip6_rt_pcpu_alloc() -> ip6_rt_get_dev_rcu() with commit 4832c30d5458 ("net: ipv6: put host and anycast routes on device with address"). KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f] RIP: 0010:ip6_rt_pcpu_alloc (net/ipv6/route.c:1418) Call Trace: ip6_pol_route (net/ipv6/route.c:2318) fib6_rule_lookup (net/ipv6/fib6_rules.c:115) ip6_route_output_flags (net/ipv6/route.c:2607) vrf_process_v6_outbound (drivers/net/vrf.c:437) I was tempted to rework the un-slaving code to clear the flag first and insert synchronize_rcu() before we remove the upper. But looks like the explicit fallback to loopback_dev is an established pattern. And I guess avoiding the synchronize_rcu() is nice, too. Fixes: 4832c30d5458 ("net: ipv6: put host and anycast routes on device with address") Reviewed-by: David Ahern Link: https://patch.msgid.link/20260301194548.927324-1-kuba@kernel.org Signed-off-by: Jakub Kicinski