Re: [PATCH] msr: Fix NULL pointer deref due to msr_open onnonexistent CPUs

[Ingo Molnar]

* Darrick J. Wong <djwong@xxxxxxxxxx> wrote:

> msr_open tests for someone trying to open a device for a nonexistent CPU.
> However, the function always returns 0, not ret like it should, hence userspace
> can BUG the kernel trivially.  This bug was introduced by the cdev lock_kernel
> pushdown patch last May.
> 
> The BUG can be reproduced with these commands:
> 
> # mknod fubar c 202 8 <-- pick a number less than NR_CPUS that is not
>                           the number of an online CPU
> # cat fubar

applied to tip/x86/urgent - thanks Darrick.

	Ingo
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