[PATCH] arm: put_user: fix possible data corruption in put_user

[Nicolas Pitre]

On Mon, 5 May 2014, Andrey Ryabinin wrote:

> On 05/05/14 13:01, Russell King - ARM Linux wrote:
> > On Mon, May 05, 2014 at 10:13:58AM +0400, Andrey Ryabinin wrote:
> >> According to arm procedure call standart r2 register is call-cloberred.
> >> So after the result of x expression was put into r2 any following
> >> function call in p may overwrite r2. To fix this, the result of p
> >> expression must be saved to the temporary variable before the
> >> assigment x expression to __r2.
> > 
> > This and the patch make no sense.  You talk about r2, but you're doing
> > nothing with r2 in the patch.
> > 
> 
> No, you didn't get it. I'll try to explain better.
> 
> Lets consider following example:
[...]

Thanks for the test code.  I do confirm there is indeed a problem.

I'm trying to make sure your patch is actually the best fix.


Nicolas