sctp: suspicious rcu_dereference_check() usage in sctp_epaddr_lookup_transport

[Dmitry Vyukov]

Hello,

I am getting the following reports while running syzkaller fuzzer:

[ INFO: suspicious RCU usage. ]
4.9.0+ #85 Not tainted
-------------------------------
./include/linux/rhashtable.h:572 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 0
1 lock held by syz-executor1/18023:
#0: (sk_lock-AF_INET){+.+.+.}, at: [< inline >] lock_sock
include/net/sock.h:1454
#0: (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff87bb3ccf>]
sctp_getsockopt+0x45f/0x6800 net/sctp/socket.c:6432

stack backtrace:
CPU: 2 PID: 18023 Comm: syz-executor1 Not tainted 4.9.0+ #85
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[< none >] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
[< none >] lockdep_rcu_suspicious+0x139/0x180
kernel/locking/lockdep.c:4448
[< inline >] __rhashtable_lookup ./include/linux/rhashtable.h:572
[< inline >] rhltable_lookup ./include/linux/rhashtable.h:660
[< none >] sctp_epaddr_lookup_transport+0x641/0x930
net/sctp/input.c:946
[< none >] sctp_endpoint_lookup_assoc+0x83/0x120
net/sctp/endpointola.c:335
[< none >] sctp_addr_id2transport+0xaf/0x1e0 net/sctp/socket.c:241
[< none >] sctp_getsockopt_peer_addr_info+0x216/0x630
net/sctp/socket.c:4625
[< none >] sctp_getsockopt+0x2860/0x6800 net/sctp/socket.c:6500
[< none >] sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:2685
[< inline >] SYSC_getsockopt net/socket.c:1819
[< none >] SyS_getsockopt+0x245/0x380 net/socket.c:1801
[< none >] entry_SYSCALL_64_fastpath+0x23/0xc6
arch/x86/entry/entry_64.S:203

On commit e7aa8c2eb11ba69b1b69099c3c7bd6be3087b0ba (Dec 12).

[Marcelo Ricardo Leitner]

I think this was introduced in the rhlist converstion. We had removed
some rcu_read_lock() calls on sctp stack because rhashtable was already
calling it, but then we didn't add them back when moving to rhlist.

This code:
+/* return a transport without holding it, as it's only used under sock lock */
struct sctp_transport *sctp_epaddr_lookup_transport(
const struct sctp_endpoint *ep,
const union sctp_addr *paddr)
{
struct net *net = sock_net(ep->base.sk);
+ struct rhlist_head *tmp, *list;
+ struct sctp_transport *t;
struct sctp_hash_cmp_arg arg = {
- .ep = ep,
.paddr = paddr,
.net = net,
+ .lport = htons(ep->base.bind_addr.port),
};

- return rhashtable_lookup_fast(&sctp_transport_hashtable, &arg,
- sctp_hash_params);
+ list = rhltable_lookup(&sctp_transport_hashtable, &arg,
+ sctp_hash_params);

Had an implicit rcu_read_lock() on rhashtable_lookup_fast, but it
doesn't on rhltable_lookup and rhltable_lookup uses _rcu calls which
assumes we have rcu read protection.

Marcelo

[Xin Long]

You're right, we need to call rcu_read_lock before using rhltable_lookup.
will post a fix for it, thanks.