This is a note to let you know that I've just added the patch titled

ipv6: fix possible deadlock in rt6_age_examine_exception()

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: ipv6-fix-possible-deadlock-in-rt6_age_examine_exception.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 1bfa26ff8c4b7512f4e4efa6df211239223033d4 Mon Sep 17 00:00:00 2001

From: Eric Dumazet edumazet@google.com Date: Fri, 23 Mar 2018 07:56:58 -0700 Subject: ipv6: fix possible deadlock in rt6_age_examine_exception()

From: Eric Dumazet edumazet@google.com

commit 1bfa26ff8c4b7512f4e4efa6df211239223033d4 upstream.

syzbot reported a LOCKDEP splat [1] in rt6_age_examine_exception()

rt6_age_examine_exception() is called while rt6_exception_lock is held. This lock is the lower one in the lock hierarchy, thus we can not call dst_neigh_lookup() function, as it can fallback to neigh_create()

We should instead do a pure RCU lookup. As a bonus we avoid a pair of atomic operations on neigh refcount.

[1]

WARNING: possible circular locking dependency detected 4.16.0-rc4+ #277 Not tainted

syz-executor7/4015 is trying to acquire lock: (&ndev->lock){++--}, at: [<00000000416dce19>] __ipv6_dev_mc_dec+0x45/0x350 net/ipv6/mcast.c:928

but task is already holding lock: (&tbl->lock){++-.}, at: [<00000000b5cb1d65>] neigh_ifdown+0x3d/0x250 net/core/neighbour.c:292

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&tbl->lock){++-.}: __raw_write_lock_bh include/linux/rwlock_api_smp.h:203 [inline] _raw_write_lock_bh+0x31/0x40 kernel/locking/spinlock.c:312 __neigh_create+0x87e/0x1d90 net/core/neighbour.c:528 neigh_create include/net/neighbour.h:315 [inline] ip6_neigh_lookup+0x9a7/0xba0 net/ipv6/route.c:228 dst_neigh_lookup include/net/dst.h:405 [inline] rt6_age_examine_exception net/ipv6/route.c:1609 [inline] rt6_age_exceptions+0x381/0x660 net/ipv6/route.c:1645 fib6_age+0xfb/0x140 net/ipv6/ip6_fib.c:2033 fib6_clean_node+0x389/0x580 net/ipv6/ip6_fib.c:1919 fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1845 fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1893 fib6_clean_tree+0x1e6/0x340 net/ipv6/ip6_fib.c:1970 __fib6_clean_all+0x1f4/0x3a0 net/ipv6/ip6_fib.c:1986 fib6_clean_all net/ipv6/ip6_fib.c:1997 [inline] fib6_run_gc+0x16b/0x3c0 net/ipv6/ip6_fib.c:2053 ndisc_netdev_event+0x3c2/0x4a0 net/ipv6/ndisc.c:1781 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93 __raw_notifier_call_chain kernel/notifier.c:394 [inline] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401 call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1707 call_netdevice_notifiers net/core/dev.c:1725 [inline] __dev_notify_flags+0x262/0x430 net/core/dev.c:6960 dev_change_flags+0xf5/0x140 net/core/dev.c:6994 devinet_ioctl+0x126a/0x1ac0 net/ipv4/devinet.c:1080 inet_ioctl+0x184/0x310 net/ipv4/af_inet.c:919 sock_do_ioctl+0xef/0x390 net/socket.c:957 sock_ioctl+0x36b/0x610 net/socket.c:1081 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #2 (rt6_exception_lock){+.-.}: __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168 spin_lock_bh include/linux/spinlock.h:315 [inline] rt6_flush_exceptions+0x21/0x210 net/ipv6/route.c:1367 fib6_del_route net/ipv6/ip6_fib.c:1677 [inline] fib6_del+0x624/0x12c0 net/ipv6/ip6_fib.c:1761 __ip6_del_rt+0xc7/0x120 net/ipv6/route.c:2980 ip6_del_rt+0x132/0x1a0 net/ipv6/route.c:2993 __ipv6_dev_ac_dec+0x3b1/0x600 net/ipv6/anycast.c:332 ipv6_dev_ac_dec net/ipv6/anycast.c:345 [inline] ipv6_sock_ac_close+0x2b4/0x3e0 net/ipv6/anycast.c:200 inet6_release+0x48/0x70 net/ipv6/af_inet6.c:433 sock_release+0x8d/0x1e0 net/socket.c:594 sock_close+0x16/0x20 net/socket.c:1149 __fput+0x327/0x7e0 fs/file_table.c:209 ____fput+0x15/0x20 fs/file_table.c:243 task_work_run+0x199/0x270 kernel/task_work.c:113 exit_task_work include/linux/task_work.h:22 [inline] do_exit+0x9bb/0x1ad0 kernel/exit.c:865 do_group_exit+0x149/0x400 kernel/exit.c:968 get_signal+0x73a/0x16d0 kernel/signal.c:2469 do_signal+0x90/0x1e90 arch/x86/kernel/signal.c:809 exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:162 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline] syscall_return_slowpath arch/x86/entry/common.c:265 [inline] do_syscall_64+0x6ec/0x940 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #1 (&(&tb->tb6_lock)->rlock){+.-.}: __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168 spin_lock_bh include/linux/spinlock.h:315 [inline] __ip6_ins_rt+0x56/0x90 net/ipv6/route.c:1007 ip6_route_add+0x141/0x190 net/ipv6/route.c:2955 addrconf_prefix_route+0x44f/0x620 net/ipv6/addrconf.c:2359 fixup_permanent_addr net/ipv6/addrconf.c:3368 [inline] addrconf_permanent_addr net/ipv6/addrconf.c:3391 [inline] addrconf_notify+0x1ad2/0x2310 net/ipv6/addrconf.c:3460 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93 __raw_notifier_call_chain kernel/notifier.c:394 [inline] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401 call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1707 call_netdevice_notifiers net/core/dev.c:1725 [inline] __dev_notify_flags+0x15d/0x430 net/core/dev.c:6958 dev_change_flags+0xf5/0x140 net/core/dev.c:6994 do_setlink+0xa22/0x3bb0 net/core/rtnetlink.c:2357 rtnl_newlink+0xf37/0x1a50 net/core/rtnetlink.c:2965 rtnetlink_rcv_msg+0x57f/0xb10 net/core/rtnetlink.c:4641 netlink_rcv_skb+0x14b/0x380 net/netlink/af_netlink.c:2444 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4659 netlink_unicast_kernel net/netlink/af_netlink.c:1308 [inline] netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1334 netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1897 sock_sendmsg_nosec net/socket.c:629 [inline] sock_sendmsg+0xca/0x110 net/socket.c:639 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2047 __sys_sendmsg+0xe5/0x210 net/socket.c:2081 SYSC_sendmsg net/socket.c:2092 [inline] SyS_sendmsg+0x2d/0x50 net/socket.c:2088 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (&ndev->lock){++--}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920 __raw_write_lock_bh include/linux/rwlock_api_smp.h:203 [inline] _raw_write_lock_bh+0x31/0x40 kernel/locking/spinlock.c:312 __ipv6_dev_mc_dec+0x45/0x350 net/ipv6/mcast.c:928 ipv6_dev_mc_dec+0x110/0x1f0 net/ipv6/mcast.c:961 pndisc_destructor+0x21a/0x340 net/ipv6/ndisc.c:392 pneigh_ifdown net/core/neighbour.c:695 [inline] neigh_ifdown+0x149/0x250 net/core/neighbour.c:294 rt6_disable_ip+0x537/0x700 net/ipv6/route.c:3874 addrconf_ifdown+0x14b/0x14f0 net/ipv6/addrconf.c:3633 addrconf_notify+0x5f8/0x2310 net/ipv6/addrconf.c:3557 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93 __raw_notifier_call_chain kernel/notifier.c:394 [inline] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401 call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1707 call_netdevice_notifiers net/core/dev.c:1725 [inline] __dev_notify_flags+0x262/0x430 net/core/dev.c:6960 dev_change_flags+0xf5/0x140 net/core/dev.c:6994 devinet_ioctl+0x126a/0x1ac0 net/ipv4/devinet.c:1080 inet_ioctl+0x184/0x310 net/ipv4/af_inet.c:919 packet_ioctl+0x1ff/0x310 net/packet/af_packet.c:4066 sock_do_ioctl+0xef/0x390 net/socket.c:957 sock_ioctl+0x36b/0x610 net/socket.c:1081 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7

other info that might help us debug this:

Chain exists of: &ndev->lock --> rt6_exception_lock --> &tbl->lock

Possible unsafe locking scenario:

CPU0 CPU1 ---- ---- lock(&tbl->lock); lock(rt6_exception_lock); lock(&tbl->lock); lock(&ndev->lock);

*** DEADLOCK ***

2 locks held by syz-executor7/4015: #0: (rtnl_mutex){+.+.}, at: [<00000000a2f16daa>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74 #1: (&tbl->lock){++-.}, at: [<00000000b5cb1d65>] neigh_ifdown+0x3d/0x250 net/core/neighbour.c:292

stack backtrace: CPU: 0 PID: 4015 Comm: syz-executor7 Not tainted 4.16.0-rc4+ #277 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x24d lib/dump_stack.c:53 print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223 check_prev_add kernel/locking/lockdep.c:1863 [inline] check_prevs_add kernel/locking/lockdep.c:1976 [inline] validate_chain kernel/locking/lockdep.c:2417 [inline] __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920 __raw_write_lock_bh include/linux/rwlock_api_smp.h:203 [inline] _raw_write_lock_bh+0x31/0x40 kernel/locking/spinlock.c:312 __ipv6_dev_mc_dec+0x45/0x350 net/ipv6/mcast.c:928 ipv6_dev_mc_dec+0x110/0x1f0 net/ipv6/mcast.c:961 pndisc_destructor+0x21a/0x340 net/ipv6/ndisc.c:392 pneigh_ifdown net/core/neighbour.c:695 [inline] neigh_ifdown+0x149/0x250 net/core/neighbour.c:294 rt6_disable_ip+0x537/0x700 net/ipv6/route.c:3874 addrconf_ifdown+0x14b/0x14f0 net/ipv6/addrconf.c:3633 addrconf_notify+0x5f8/0x2310 net/ipv6/addrconf.c:3557 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93 __raw_notifier_call_chain kernel/notifier.c:394 [inline] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401 call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1707 call_netdevice_notifiers net/core/dev.c:1725 [inline] __dev_notify_flags+0x262/0x430 net/core/dev.c:6960 dev_change_flags+0xf5/0x140 net/core/dev.c:6994 devinet_ioctl+0x126a/0x1ac0 net/ipv4/devinet.c:1080 inet_ioctl+0x184/0x310 net/ipv4/af_inet.c:919 packet_ioctl+0x1ff/0x310 net/packet/af_packet.c:4066 sock_do_ioctl+0xef/0x390 net/socket.c:957 sock_ioctl+0x36b/0x610 net/socket.c:1081 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Fixes: c757faa8bfa2 ("ipv6: prepare fib6_age() for exception table") Signed-off-by: Eric Dumazet edumazet@google.com Cc: Wei Wang weiwan@google.com Cc: Martin KaFai Lau kafai@fb.com Acked-by: Wei Wang weiwan@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- net/ipv6/route.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1627,11 +1627,10 @@ static void rt6_age_examine_exception(st struct neighbour *neigh; __u8 neigh_flags = 0;

- neigh = dst_neigh_lookup(&rt->dst, &rt->rt6i_gateway); - if (neigh) { + neigh = __ipv6_neigh_lookup_noref(rt->dst.dev, &rt->rt6i_gateway); + if (neigh) neigh_flags = neigh->flags; - neigh_release(neigh); - } + if (!(neigh_flags & NTF_ROUTER)) { RT6_TRACE("purging route %p via non-router but gateway\n", rt); @@ -1655,7 +1654,8 @@ void rt6_age_exceptions(struct rt6_info if (!rcu_access_pointer(rt->rt6i_exception_bucket)) return;

- spin_lock_bh(&rt6_exception_lock); + rcu_read_lock_bh(); + spin_lock(&rt6_exception_lock); bucket = rcu_dereference_protected(rt->rt6i_exception_bucket, lockdep_is_held(&rt6_exception_lock));

@@ -1669,7 +1669,8 @@ void rt6_age_exceptions(struct rt6_info bucket++; } } - spin_unlock_bh(&rt6_exception_lock); + spin_unlock(&rt6_exception_lock); + rcu_read_unlock_bh(); }

struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,

Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.15/netfilter-bridge-ebt_among-add-more-missing-match-size-checks.patch queue-4.15/ipv6-fix-possible-deadlock-in-rt6_age_examine_exception.patch