[Devel] [PATCH] autofs: fix autofs_v5_packet structure for compat mode

[Stanislav Kinsburskiy]

31.08.2017 13:38, Dmitry V. Levin пишет:
> On Thu, Aug 31, 2017 at 02:11:34PM +0400, Stanislav Kinsburskiy wrote:
>> Due to integer variables alignment size of struct autofs_v5_packet in 300
>> bytes in 32-bit architectures (instead of 304 bytes in 64-bits architectures).
>>
>> This may lead to memory corruption (64 bits kernel always send 304 bytes,
>> while 32-bit userspace application expects for 300).
>>
>> https://jira.sw.ru/browse/PSBM-71078
>>
>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
>> ---
>>  include/uapi/linux/auto_fs4.h |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/include/uapi/linux/auto_fs4.h b/include/uapi/linux/auto_fs4.h
>> index e02982f..8729a47 100644
>> --- a/include/uapi/linux/auto_fs4.h
>> +++ b/include/uapi/linux/auto_fs4.h
>> @@ -137,6 +137,8 @@ struct autofs_v5_packet {
>>  	__u32 pid;
>>  	__u32 tgid;
>>  	__u32 len;
>> +	__u32 blob;		/* This is needed to align structure up to 8
>> +				   bytes for ALL archs including 32-bit */
>>  	char name[NAME_MAX+1];
>>  };
> 
> This change breaks ABI because it changes offsetof(struct autofs_v5_packet, name).
> If you need to fix the alignment, use  __attribute__((aligned(8))).
> 

Nice to know you're watching.
Yes, attribute is better.
But how ABI is broken? On x86_64 this alignment is implied, so nothing is changed.

> An alignment change would also be an ABI breakage on 32-bit architectures,
> though.
> 

True.
But from my POW better have it working on 64bit archs for 32bit apps.
But anyway, upstream guys will device, whether they want 32-bit autofs applications properly work on 64 or 32 bits.