Re: [PATCH] staging: ion: fix corruption of ion_import_dma_buf

[Colin Cross]

On Wed, Sep 9, 2015 at 10:19 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> (adding Colin and John)
>
>
> On 09/09/2015 12:41 AM, Shawn Lin wrote:
>>
>> we found this issue but still exit in lastest kernel. Simply
>> keep ion_handle_create under mutex_lock to avoid this race.
>>
>> WARNING: CPU: 2 PID: 2648 at drivers/staging/android/ion/ion.c:512
>> ion_handle_add+0xb4/0xc0()
>> ion_handle_add: buffer already found.
>> Modules linked in: iwlmvm iwlwifi mac80211 cfg80211 compat
>> CPU: 2 PID: 2648 Comm: TimedEventQueue Tainted: G        W    3.14.0 #7
>>   00000000 00000000 9a3efd2c 80faf273 9a3efd6c 9a3efd5c 80935dc9 811d7fd3
>>   9a3efd88 00000a58 812208a0 00000200 80e128d4 80e128d4 8d4ae00c a8cd8600
>>   a8cd8094 9a3efd74 80935e0e 00000009 9a3efd6c 811d7fd3 9a3efd88 9a3efd9c
>> Call Trace:
>>    [<80faf273>] dump_stack+0x48/0x69
>>    [<80935dc9>] warn_slowpath_common+0x79/0x90
>>    [<80e128d4>] ? ion_handle_add+0xb4/0xc0
>>    [<80e128d4>] ? ion_handle_add+0xb4/0xc0
>>    [<80935e0e>] warn_slowpath_fmt+0x2e/0x30
>>    [<80e128d4>] ion_handle_add+0xb4/0xc0
>>    [<80e144cc>] ion_import_dma_buf+0x8c/0x110
>>    [<80c517c4>] reg_init+0x364/0x7d0
>>    [<80993363>] ? futex_wait+0x123/0x210
>>    [<80992e0e>] ? get_futex_key+0x16e/0x1e0
>>    [<8099308f>] ? futex_wake+0x5f/0x120
>>    [<80c51e19>] vpu_service_ioctl+0x1e9/0x500
>>    [<80994aec>] ? do_futex+0xec/0x8e0
>>    [<80971080>] ? prepare_to_wait_event+0xc0/0xc0
>>    [<80c51c30>] ? reg_init+0x7d0/0x7d0
>>    [<80a22562>] do_vfs_ioctl+0x2d2/0x4c0
>>    [<80b198ad>] ? inode_has_perm.isra.41+0x2d/0x40
>>    [<80b199cf>] ? file_has_perm+0x7f/0x90
>>    [<80b1a5f7>] ? selinux_file_ioctl+0x47/0xf0
>>    [<80a227a8>] SyS_ioctl+0x58/0x80
>>    [<80fb45e8>] syscall_call+0x7/0x7
>>    [<80fb0000>] ? mmc_do_calc_max_discard+0xab/0xe4
>>
>> Fixes: 83271f626 ("ion: hold reference to handle...")
>> Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
>> ---
>>
>>   drivers/staging/android/ion/ion.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/staging/android/ion/ion.c
>> b/drivers/staging/android/ion/ion.c
>> index eec878e..32e7b5c 100644
>> --- a/drivers/staging/android/ion/ion.c
>> +++ b/drivers/staging/android/ion/ion.c
>> @@ -1179,13 +1179,13 @@ struct ion_handle *ion_import_dma_buf(struct
>> ion_client *client, int fd)
>>                 mutex_unlock(&client->lock);
>>                 goto end;
>>         }
>> -       mutex_unlock(&client->lock);
>>
>>         handle = ion_handle_create(client, buffer);
>> -       if (IS_ERR(handle))
>> +       if (IS_ERR(handle)) {
>> +               mutex_unlock(&client->lock);
>>                 goto end;
>> +       }
>>
>> -       mutex_lock(&client->lock);
>>         ret = ion_handle_add(client, handle);
>>         mutex_unlock(&client->lock);
>>         if (ret) {
>>
>
> So the patch looks correct but the locking change there seems like it was
> added
> deliberately. Colin/John, do you remember why the locking for
> ion_import_dma_buf
> changed? Was there a deadlock condition somewhere?
>
> Thanks,
> Laura

I can't see any reason to not hold the mutex across ion_handle_create.
The patch that introduced the bug
(83271f6262c91a49df325c52bec8f00f4de294ca, ion: hold reference to
handle after ion_uhandle_get) required that the mutex not be held
around the call to ion_handle_put, but didn't affect
ion_handle_create.
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