[Devel] [PATCH RHEL7 COMMIT] ms/net/packet: fix a race in packet_bind() and packet_notifier()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-862.14.4.vz7.72.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-862.14.4.vz7.72.14
------>
commit a5525b0f6d9f98100a46ac25d21b1e2b67e2783c
Author: Eric Dumazet <edumazet at google.com>
Date:   Mon Oct 29 12:08:00 2018 +0300

    ms/net/packet: fix a race in packet_bind() and packet_notifier()
    
    Commit 15fe076edea787807a7cdc168df832544b58eba6 in the mainline kernel.
    
    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 hooks again the socket right before
    first thread is able to grab again po->bind_lock.
    
    Fixes this issue by temporarily setting po->num to 0, as suggested by
    David Miller.
    
    [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 at google.com>
    Reported-by: syzbot <syzkaller at googlegroups.com>
    Cc: Francesco Ruggeri <fruggeri at aristanetworks.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    CVE-2018-18559
    https://jira.sw.ru/browse/PSBM-89677
    
    Signed-off-by: Evgenii Shatokhin <eshatokhin at virtuozzo.com>
---
 net/packet/af_packet.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0de7ea414850..30b8e900e936 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2731,6 +2731,10 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
 	if (need_rehook) {
 		if (po->running) {
 			rcu_read_unlock();
+			/* prevents packet_notifier() from calling
+			 * register_prot_hook()
+			 */
+			po->num = 0;
 			__unregister_prot_hook(sk, true);
 			rcu_read_lock();
 			dev_curr = po->prot_hook.dev;
@@ -2739,6 +2743,7 @@ 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;