Re: [PATCH V2] futex: Fix the write access fault problem for real

From: Linus Torvalds
Date: Wed Jun 24 2009 - 12:48:11 EST




On Wed, 24 Jun 2009, Thomas Gleixner wrote:
>
> The solution is to not rely on access_ok and get_user() for any write
> access related fault on private and shared futexes. Instead we need to
> fault it in with verification of write access.
>
> There is no generic non destructive write mechanism which would fault
> the user page in trough a #PF, but as we already know that we will
> fault we can as well call get_user_pages() directly and avoid the #PF
> overhead.

Ack. Patch looks saner this way, and the commit message explains the
issues.

Linus
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