Re: [PATCH] mm: fix protection of mm_struct fields in get_cmdline()

[Konstantin Khlebnikov <khlebnikov@yandex-team.ru>]

On 15.05.2019 11:22, Oscar Salvador wrote:
> On Wed, May 15, 2019 at 11:15:37AM +0300, Konstantin Khlebnikov wrote:
>> Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|
>> end and env_start|end in mm_struct") related mm fields are protected with
>> separate spinlock and mmap_sem held for read is not enough for protection.
>>
>> Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> 
> This was already addressed by [1]?

Yep.

> 
> [1] https://patchwork.kernel.org/patch/10923003/
> 
>> ---
>>   mm/util.c |    4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index e2e4f8c3fa12..540e7c157cf2 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -717,12 +717,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
>>   	if (!mm->arg_end)
>>   		goto out_mm;	/* Shh! No looking before we're done */
>>   
>> -	down_read(&mm->mmap_sem);
>> +	spin_lock(&mm->arg_lock);
>>   	arg_start = mm->arg_start;
>>   	arg_end = mm->arg_end;
>>   	env_start = mm->env_start;
>>   	env_end = mm->env_end;
>> -	up_read(&mm->mmap_sem);
>> +	spin_unlock(&mm->arg_lock);
>>   
>>   	len = arg_end - arg_start;
>>   
>>
>