[Devel] [RFC PATCH 2/2] autofs: sent 32-bit sized packet for 32-bit process

[Stanislav Kinsburskiy]

31.08.2017 20:22, Dmitry V. Levin пишет:
> On Thu, Aug 31, 2017 at 05:57:11PM +0400, Stanislav Kinsburskiy wrote:
>> The structure autofs_v5_packet (except name) is not aligned by 8 bytes, which
>> lead to different sizes in 32 and 64-bit architectures.
>> Let's form 32-bit compatible packet when daemon has 32-bit addressation.
>>
>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
>> ---
>>  fs/autofs4/waitq.c |   11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
>> index 309ca6b..484cf2e 100644
>> --- a/fs/autofs4/waitq.c
>> +++ b/fs/autofs4/waitq.c
>> @@ -153,12 +153,19 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
>>  	{
>>  		struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet;
>>  		struct user_namespace *user_ns = sbi->pipe->f_cred->user_ns;
>> +		size_t name_offset;
>>  
>> -		pktsz = sizeof(*packet);
>> +		if (sbi->is32bit)
>> +			name_offset = offsetof(struct autofs_v5_packet, len) +
>> +				      sizeof(packet->len);
>> +		else
>> +			name_offset = offsetof(struct autofs_v5_packet, name);
> 
> This doesn't help at all because the offset of struct autofs_v5_packet.name
> does not change.
> 
>> +		pktsz = name_offset + sizeof(packet->name);
> 
> What changes is pktsz: it's either sizeof(struct autofs_v5_packet)
> or 4 bytes less, depending on the architecture.

Indeed. Thanks!

> For example,
> 
> #ifdef CONFIG_COMPAT
> 	if (__alignof__(compat_u64) < __alignof__(u64) && sbi->is32bit)

Unfortunately I don't get this "alignof" checks.
The intention of "is32bit" was to define this compat case completely.
Why are they required?

> 		pktsz = offsetofend(struct autofs_v5_packet, name);
> 	else
> #endif
> 	pktsz = sizeof(*packet);
> 
>