Re: suspicious RCU usage at net/tipc/bearer.c:LINE

[Dmitry Vyukov]

On Thu, Feb 1, 2018 at 11:22 PM, Eric Biggers <ebiggers3@xxxxxxxxx> wrote:
> On Sun, Dec 31, 2017 at 10:58:01AM -0800, syzbot wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> 5aa90a84589282b87666f92b6c3c917c8080a9bf
>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached
>> Raw console output is attached.
>> C reproducer is attached
>> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>> for information about syzkaller reproducers
>>
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+6345fd433db009b29413@xxxxxxxxxxxxxxxxxxxxxxxxx
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>> audit: type=1400 audit(1514679888.244:9): avc:  denied  { write } for
>> pid=3194 comm="syzkaller021477" path="socket:[11143]" dev="sockfs" ino=11143
>> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
>> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
>> tclass=netlink_generic_socket permissive=1
>> =============================
>> WARNING: suspicious RCU usage
>> 4.15.0-rc5+ #152 Not tainted
>> -----------------------------
>> net/tipc/bearer.c:177 suspicious rcu_dereference_protected() usage!
>>
>> other info that might help us debug this:
>>
>>
>> rcu_scheduler_active = 2, debug_locks = 1
>> 2 locks held by syzkaller021477/3194:
>>  #0:  (cb_lock){++++}, at: [<00000000d20133ea>] genl_rcv+0x19/0x40
>> net/netlink/genetlink.c:634
>>  #1:  (genl_mutex){+.+.}, at: [<00000000fcc5d1bc>] genl_lock
>> net/netlink/genetlink.c:33 [inline]
>>  #1:  (genl_mutex){+.+.}, at: [<00000000fcc5d1bc>] genl_rcv_msg+0x115/0x140
>> net/netlink/genetlink.c:622
>>
>> stack backtrace:
>> CPU: 1 PID: 3194 Comm: syzkaller021477 Not tainted 4.15.0-rc5+ #152
>> 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+0x194/0x257 lib/dump_stack.c:53
>>  lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4585
>>  tipc_bearer_find+0x2b4/0x3b0 net/tipc/bearer.c:177
>>  tipc_nl_compat_link_set+0x329/0x9f0 net/tipc/netlink_compat.c:729
>>  __tipc_nl_compat_doit net/tipc/netlink_compat.c:288 [inline]
>>  tipc_nl_compat_doit+0x15b/0x660 net/tipc/netlink_compat.c:335
>>  tipc_nl_compat_handle net/tipc/netlink_compat.c:1119 [inline]
>>  tipc_nl_compat_recv+0x112f/0x18f0 net/tipc/netlink_compat.c:1201
>>  genl_family_rcv_msg+0x7b7/0xfb0 net/netlink/genetlink.c:599
>>  genl_rcv_msg+0xb2/0x140 net/netlink/genetlink.c:624
>>  netlink_rcv_skb+0x21e/0x460 net/netlink/af_netlink.c:2408
>>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:635
>>  netlink_unicast_kernel net/netlink/af_netlink.c:1275 [inline]
>>  netlink_unicast+0x4e8/0x6f0 net/netlink/af_netlink.c:1301
>>  netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1864
>>  sock_sendmsg_nosec net/socket.c:636 [inline]
>>  sock_sendmsg+0xca/0x110 net/socket.c:646
>>  sock_write_iter+0x31a/0x5d0 net/socket.c:915
>>  call_write_iter include/linux/fs.h:1772 [inline]
>>  new_sync_write fs/read_write.c:469 [inline]
>>  __vfs_write+0x684/0x970 fs/read_write.c:482
>>  vfs_write+0x189/0x510 fs/read_write.c:544
>>  SYSC_write fs/read_write.c:589 [inline]
>>  SyS_write+0xef/0x220 fs/read_write.c:581
>>  do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
>>  do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
>>  entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
>>
>
> This is still happening; looks like a missing lock in tipc_nl_compat_link_set().
> Note that the reproducer isn't guaranteed to work as-is because the message it
> sends to the netlink socket assumes that the "TIPC" generic netlink family was
> assigned ID 31, when actually it is a dynamically assigned ID.  But it will
> trigger if you adjust the message's ->nlmsg_type accordingly.


#syz dup: WARNING: suspicious RCU usage in tipc_bearer_find