sctp: suspicious rcu_dereference_check() usage in sctp_epaddr_lookup_transport

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).

Re: sctp: suspicious rcu_dereference_check() usage in sctp_epaddr_lookup_transport

[Marcelo Ricardo Leitner]

On Tue, Dec 13, 2016 at 07:07:01PM +0100, Dmitry Vyukov wrote:
> 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

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

Re: sctp: suspicious rcu_dereference_check() usage in sctp_epaddr_lookup_transport

[Xin Long]

On Wed, Dec 14, 2016 at 5:37 AM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> On Tue, Dec 13, 2016 at 07:07:01PM +0100, Dmitry Vyukov wrote:
>> 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
>
> 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.

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