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Date: Tue, 28 Nov 2017 02:23:44 -0800
From: Francesco Ruggeri <fruggeri@...sta.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
Francesco Ruggeri <fruggeri@...stanetworks.com>,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net/packet: fix a race in packet_bind() and packet_notifier()
On Mon, Nov 27, 2017 at 8:00 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.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 <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Cc: Francesco Ruggeri <fruggeri@...stanetworks.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) {
Would it make sense to move the check for po->frozen to
packet_notifier(NETDEV_UP)?
As far as I can tell that is the only case today that can cause this
race condition, and if new cases come up in the future an error code
may be required rather than silently turning register_prot_hook() into
a noop.
Otherwise it looks fine to me.
Thanks,
Acked-by: Francesco Ruggeri <fruggeri@...sta.com>
> 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;
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