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

[syzbot]

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


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Reported-by: syzbot+6345fd...@syzkaller.appspotmail.com
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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


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[Eric Biggers]

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.

- Eric

[Dmitry Vyukov]

#syz dup: WARNING: suspicious RCU usage in tipc_bearer_find