[PATCH v1 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access_begin()

[Christophe Leroy]

Le 22/01/2020 à 18:41, Al Viro a écrit :
> On Wed, Jan 22, 2020 at 08:13:12AM -0800, Linus Torvalds wrote:
>> On Wed, Jan 22, 2020 at 5:00 AM Christophe Leroy
>> <christophe.leroy at c-s.fr> wrote:
>>>
>>> Modify filldir() and filldir64() to request the real area they need
>>> to get access to.
>>
>> Not like this.
>>
>> This makes the situation for architectures like x86 much worse, since
>> you now use "put_user()" for the previous dirent filling. Which does
>> that expensive user access setup/teardown twice again.
>>
>> So either you need to cover both the dirent's with one call, or you
>> just need to cover the whole (original) user buffer passed in. But not
>> this unholy mixing of both unsafe_put_user() and regular put_user().
> 
> I would suggest simply covering the range from dirent->d_off to
> buf->current_dir->d_name[namelen]; they are going to be close to
> each other and we need those addresses anyway...
> 

In v2, I'm covering from the beginning of parent dirent to the end of 
current dirent.

Christophe