* [PATCH] bpf: Call rcu_read_unlock() before copy_to_user()
@ 2015-01-22 15:57 Michael Holzheu
0 siblings, 0 replies; 4+ messages in thread
From: Michael Holzheu @ 2015-01-22 15:57 UTC (permalink / raw)
To: Alexei Starovoitov; +Cc: Alexei Starovoitov, Martin Schwidefsky, linux-kernel
We must not hold locks when calling copy_to_user():
BUG: sleeping function called from invalid context at mm/memory.c:3732
in_atomic(): 0, irqs_disabled(): 0, pid: 671, name: test_maps
1 lock held by test_maps/671:
#0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
Preemption disabled at:[<00000000001be3b6>] vprintk_default+0x56/0x68
CPU: 0 PID: 671 Comm: test_maps Not tainted 3.19.0-rc5-00117-g5eb11d6-dirty #424
000000001e447bb0 000000001e447c40 0000000000000002 0000000000000000
000000001e447ce0 000000001e447c58 000000001e447c58 0000000000115c8a
0000000000000000 0000000000c08246 0000000000c27e8a 000000000000000b
000000001e447ca0 000000001e447c40 0000000000000000 0000000000000000
0000000000000000 0000000000115c8a 000000001e447c40 000000001e447ca0
Call Trace:
([<0000000000115b7e>] show_trace+0x12e/0x150)
[<0000000000115c40>] show_stack+0xa0/0x100
[<00000000009b163c>] dump_stack+0x74/0xc8
[<000000000017424a>] ___might_sleep+0x23a/0x248
[<00000000002b58e8>] might_fault+0x70/0xe8
[<0000000000264230>] map_lookup_elem+0x188/0x260
[<0000000000264716>] SyS_bpf+0x20e/0x840
[<00000000009bbe3a>] system_call+0xd6/0x24c
[<000003fffd15f566>] 0x3fffd15f566
1 lock held by test_maps/671:
#0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
So call rcu_read_unlock() before copy_to_user(). We can
release the lock earlier because it is not needed for copy_to_user().
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
kernel/bpf/syscall.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -172,17 +172,16 @@ static int map_lookup_elem(union bpf_att
err = -ENOENT;
rcu_read_lock();
value = map->ops->map_lookup_elem(map, key);
+ rcu_read_unlock();
if (!value)
- goto err_unlock;
+ goto free_key;
err = -EFAULT;
if (copy_to_user(uvalue, value, map->value_size) != 0)
- goto err_unlock;
+ goto free_key;
err = 0;
-err_unlock:
- rcu_read_unlock();
free_key:
kfree(key);
err_put:
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] bpf: Call rcu_read_unlock() before copy_to_user()
@ 2015-01-22 18:03 Alexei Starovoitov
0 siblings, 0 replies; 4+ messages in thread
From: Alexei Starovoitov @ 2015-01-22 18:03 UTC (permalink / raw)
To: Michael Holzheu
Cc: Alexei Starovoitov, Martin Schwidefsky, linux-kernel, netdev
On Thu, Jan 22, 2015 at 9:54 AM, Michael Holzheu
<holzheu@linux.vnet.ibm.com> wrote:
>> > So call rcu_read_unlock() before copy_to_user(). We can
>> > release the lock earlier because it is not needed for copy_to_user().
>>
>> we cannot move the rcu unlock this way, since it protects the value.
>> So we need to copy the value while still under rcu.
>
> Ok, right. I assume you will provide the correct fix.
sure :) will do.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] bpf: Call rcu_read_unlock() before copy_to_user()
2015-01-22 17:27 Alexei Starovoitov
@ 2015-01-22 17:54 ` Michael Holzheu
0 siblings, 0 replies; 4+ messages in thread
From: Michael Holzheu @ 2015-01-22 17:54 UTC (permalink / raw)
To: Alexei Starovoitov
Cc: Alexei Starovoitov, Martin Schwidefsky, linux-kernel, netdev
On Thu, 22 Jan 2015 09:27:21 -0800
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> On Thu, Jan 22, 2015 at 7:57 AM, Michael Holzheu
> <holzheu@linux.vnet.ibm.com> wrote:
> > We must not hold locks when calling copy_to_user():
> >
> > BUG: sleeping function called from invalid context at mm/memory.c:3732
> > in_atomic(): 0, irqs_disabled(): 0, pid: 671, name: test_maps
> > 1 lock held by test_maps/671:
> > #0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
> > Preemption disabled at:[<00000000001be3b6>] vprintk_default+0x56/0x68
> >
> > CPU: 0 PID: 671 Comm: test_maps Not tainted 3.19.0-rc5-00117-g5eb11d6-dirty #424
> > 000000001e447bb0 000000001e447c40 0000000000000002 0000000000000000
> > 000000001e447ce0 000000001e447c58 000000001e447c58 0000000000115c8a
> > 0000000000000000 0000000000c08246 0000000000c27e8a 000000000000000b
> > 000000001e447ca0 000000001e447c40 0000000000000000 0000000000000000
> > 0000000000000000 0000000000115c8a 000000001e447c40 000000001e447ca0
> > Call Trace:
> > ([<0000000000115b7e>] show_trace+0x12e/0x150)
> > [<0000000000115c40>] show_stack+0xa0/0x100
> > [<00000000009b163c>] dump_stack+0x74/0xc8
> > [<000000000017424a>] ___might_sleep+0x23a/0x248
> > [<00000000002b58e8>] might_fault+0x70/0xe8
> > [<0000000000264230>] map_lookup_elem+0x188/0x260
> > [<0000000000264716>] SyS_bpf+0x20e/0x840
> > [<00000000009bbe3a>] system_call+0xd6/0x24c
> > [<000003fffd15f566>] 0x3fffd15f566
> > 1 lock held by test_maps/671:
> > #0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
> >
> > So call rcu_read_unlock() before copy_to_user(). We can
> > release the lock earlier because it is not needed for copy_to_user().
>
> we cannot move the rcu unlock this way, since it protects the value.
> So we need to copy the value while still under rcu.
Ok, right. I assume you will provide the correct fix.
> I'm puzzled how I missed this warning.
> I guess you have CONFIG_PREEMPT_RCU=y ?
Yes.
Regards,
Michael
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] bpf: Call rcu_read_unlock() before copy_to_user()
@ 2015-01-22 17:27 Alexei Starovoitov
2015-01-22 17:54 ` Michael Holzheu
0 siblings, 1 reply; 4+ messages in thread
From: Alexei Starovoitov @ 2015-01-22 17:27 UTC (permalink / raw)
To: Michael Holzheu
Cc: Alexei Starovoitov, Martin Schwidefsky, linux-kernel, netdev
On Thu, Jan 22, 2015 at 7:57 AM, Michael Holzheu
<holzheu@linux.vnet.ibm.com> wrote:
> We must not hold locks when calling copy_to_user():
>
> BUG: sleeping function called from invalid context at mm/memory.c:3732
> in_atomic(): 0, irqs_disabled(): 0, pid: 671, name: test_maps
> 1 lock held by test_maps/671:
> #0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
> Preemption disabled at:[<00000000001be3b6>] vprintk_default+0x56/0x68
>
> CPU: 0 PID: 671 Comm: test_maps Not tainted 3.19.0-rc5-00117-g5eb11d6-dirty #424
> 000000001e447bb0 000000001e447c40 0000000000000002 0000000000000000
> 000000001e447ce0 000000001e447c58 000000001e447c58 0000000000115c8a
> 0000000000000000 0000000000c08246 0000000000c27e8a 000000000000000b
> 000000001e447ca0 000000001e447c40 0000000000000000 0000000000000000
> 0000000000000000 0000000000115c8a 000000001e447c40 000000001e447ca0
> Call Trace:
> ([<0000000000115b7e>] show_trace+0x12e/0x150)
> [<0000000000115c40>] show_stack+0xa0/0x100
> [<00000000009b163c>] dump_stack+0x74/0xc8
> [<000000000017424a>] ___might_sleep+0x23a/0x248
> [<00000000002b58e8>] might_fault+0x70/0xe8
> [<0000000000264230>] map_lookup_elem+0x188/0x260
> [<0000000000264716>] SyS_bpf+0x20e/0x840
> [<00000000009bbe3a>] system_call+0xd6/0x24c
> [<000003fffd15f566>] 0x3fffd15f566
> 1 lock held by test_maps/671:
> #0: (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
>
> So call rcu_read_unlock() before copy_to_user(). We can
> release the lock earlier because it is not needed for copy_to_user().
we cannot move the rcu unlock this way, since it protects the value.
So we need to copy the value while still under rcu.
I'm puzzled how I missed this warning.
I guess you have CONFIG_PREEMPT_RCU=y ?
and if (in_atomic()) return; as part of might_fault() hid it.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2015-01-22 18:03 UTC | newest]
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2015-01-22 15:57 [PATCH] bpf: Call rcu_read_unlock() before copy_to_user() Michael Holzheu
2015-01-22 17:27 Alexei Starovoitov
2015-01-22 17:54 ` Michael Holzheu
2015-01-22 18:03 Alexei Starovoitov
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