From: Eric Dumazet <eduma...@google.com> syzbot reported crashes [1] and provided a C repro easing bug hunting.
When/if packet_do_bind() calls __unregister_prot_hook() and releases po->bind_lock, another thread can run packet_notifier() and process an NETDEV_UP event. This calls register_prot_hook() and hook again the socket right before first thread was able to grab again po->bind_lock. Fixes this issue by adding po->frozen bit : It is set and cleared by __unregister_prot_hook() if po->bind_lock needs to be released temporarily. It is tested in register_prot_hook() to prevent the race condition. [1] dev_remove_pack: ffff8801bf16fa80 not found ------------[ cut here ]------------ kernel BUG at net/core/dev.c:7945! ( BUG_ON(!list_empty(&dev->ptype_all)); ) invalid opcode: 0000 [#1] SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: device syz0 entered promiscuous mode CPU: 0 PID: 3161 Comm: syzkaller404108 Not tainted 4.14.0+ #190 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8801cc57a500 task.stack: ffff8801cc588000 RIP: 0010:netdev_run_todo+0x772/0xae0 net/core/dev.c:7945 RSP: 0018:ffff8801cc58f598 EFLAGS: 00010293 RAX: ffff8801cc57a500 RBX: dffffc0000000000 RCX: ffffffff841f75b2 RDX: 0000000000000000 RSI: 1ffff100398b1ede RDI: ffff8801bf1f8810 device syz0 entered promiscuous mode RBP: ffff8801cc58f898 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801bf1f8cd8 R13: ffff8801cc58f870 R14: ffff8801bf1f8780 R15: ffff8801cc58f7f0 FS: 0000000001716880(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020b13000 CR3: 0000000005e25000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:106 tun_detach drivers/net/tun.c:670 [inline] tun_chr_close+0x49/0x60 drivers/net/tun.c:2845 __fput+0x333/0x7f0 fs/file_table.c:210 ____fput+0x15/0x20 fs/file_table.c:244 task_work_run+0x199/0x270 kernel/task_work.c:113 exit_task_work include/linux/task_work.h:22 [inline] do_exit+0x9bb/0x1ae0 kernel/exit.c:865 do_group_exit+0x149/0x400 kernel/exit.c:968 SYSC_exit_group kernel/exit.c:979 [inline] SyS_exit_group+0x1d/0x20 kernel/exit.c:977 entry_SYSCALL_64_fastpath+0x1f/0x96 RIP: 0033:0x44ad19 Fixes: 30f7ea1c2b5f ("packet: race condition in packet_bind") Signed-off-by: Eric Dumazet <eduma...@google.com> Reported-by: syzbot <syzkal...@googlegroups.com> Cc: Francesco Ruggeri <frugg...@aristanetworks.com> --- net/packet/af_packet.c | 5 ++++- net/packet/internal.h | 1 + 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 737092ca9b4eed464b6c0907d85b679ae4da6046..64382200ab9b0701a510f16a098257ccd7ac5ff5 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -336,7 +336,7 @@ static void register_prot_hook(struct sock *sk) { struct packet_sock *po = pkt_sk(sk); - if (!po->running) { + if (!po->running && !po->frozen) { if (po->fanout) __fanout_link(sk, po); else @@ -368,9 +368,11 @@ static void __unregister_prot_hook(struct sock *sk, bool sync) __sock_put(sk); if (sync) { + po->frozen = 1; spin_unlock(&po->bind_lock); synchronize_net(); spin_lock(&po->bind_lock); + po->frozen = 0; } } @@ -3105,6 +3107,7 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex, dev->ifindex); } + BUG_ON(po->running); po->num = proto; po->prot_hook.type = proto; diff --git a/net/packet/internal.h b/net/packet/internal.h index 562fbc155006374862e5bfdd78b65a7f46210bea..e039af6e71d650e3beb2936af6cbdd167313499e 100644 --- a/net/packet/internal.h +++ b/net/packet/internal.h @@ -114,6 +114,7 @@ struct packet_sock { spinlock_t bind_lock; struct mutex pg_vec_lock; unsigned int running:1, /* prot_hook is attached*/ + frozen:1, auxdata:1, origdev:1, has_vnet_hdr:1;