x86/apic: Fix parsing of the 'lapic' cmdline option

commit 27cf929845b10043f2257693c7d179a9e0b1980e upstream.

Including " lapic " in the kernel cmdline on an x86-64 kernel
makes it panic while parsing early params -- e.g. with no user
visible output.

Fix this bug by ensuring arg is non-NULL before passing it to
strncmp().

Reported-by: PaX Team <pageexec@freemail.hu>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1361303227-13174-1-git-send-email-minipli@googlemail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b994cc84aa7e0f0654775f82b286c77d28d9d621..cbf5121fdd2bee68d3452d65cb1d9b978c17b4f1 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -131,7 +131,7 @@ static int __init parse_lapic(char *arg)
 {
        if (config_enabled(CONFIG_X86_32) && !arg)
                force_enable_local_apic = 1;
-       else if (!strncmp(arg, "notscdeadline", 13))
+       else if (arg && !strncmp(arg, "notscdeadline", 13))
                setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
        return 0;
 }