tree c11b892999c65d8b1d805191f88b15bf4a058be2
parent a6825f1c1fa83b1e92b6715ee5771a4d6524d3b9
author Darrick J. Wong <djwong@us.ibm.com> 1218753813 -0700
committer Ingo Molnar <mingo@elte.hu> 1218800310 +0200

x86, msr: fix NULL pointer deref due to msr_open on nonexistent CPUs

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

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>