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

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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>
This commit is contained in:
Darrick J. Wong 2008-08-14 15:43:33 -07:00 committed by Ingo Molnar
parent a6825f1c1f
commit 967060d00d
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/msr.c
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@ -131,7 +131,7 @@ static int msr_open(struct inode *inode, struct file *file)
ret = -EIO; /* MSR not supported */
out:
unlock_kernel();
return 0;
return ret;
}
/*