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 <holz...@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:
--
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