kdb: do a sanity check on the cpu in kdb_per_cpu()
The "whichcpu" comes from argv[3].  The cpu_online() macro looks up the
cpu in a bitmap of online cpus, but if the value is too high then it
could read beyond the end of the bitmap and possibly Oops.
Fixes: 5d5314d679 ("kdb: core for kgdb back end (1 of 2)")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
			
			
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				| @ -2583,7 +2583,7 @@ static int kdb_per_cpu(int argc, const char **argv) | ||||
| 		diag = kdbgetularg(argv[3], &whichcpu); | ||||
| 		if (diag) | ||||
| 			return diag; | ||||
| 		if (!cpu_online(whichcpu)) { | ||||
| 		if (whichcpu >= nr_cpu_ids || !cpu_online(whichcpu)) { | ||||
| 			kdb_printf("cpu %ld is not online\n", whichcpu); | ||||
| 			return KDB_BADCPUNUM; | ||||
| 		} | ||||
|  | ||||
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