[PATCH] arm64/smp: check !ipi_desc[i] in arch_show_interrupts

[Chen Jun]

There is a potential dereferencing null pointer issue in
arch_show_interrupts.

Problem 1:
int arch_show_interrupts(struct seq_file *p, int prec)
        for (i = 0; i < NR_IPI; i++) {
                seq_printf(p, "%10u ", irq_desc_kstat_cpu(ipi_desc[i],
			cpu));

Only ipi_desc[0..nr_ipi - 1] are initialized in set_smp_ipi_range.
and ipi_desc[nr_ipi..NR_IPI] are NULL.
irq_desc_kstat_cpu will dereference NULL pointer.
For now, the problem can not be triggered, because NR_IPI is always
equal to nr_ipi.

Problem 2:
If request_percpu_irq failed in set_smp_ipi_range, ipi_desc[i]
would be NULL.
irq_desc_kstat_cpu will dereference NULL pointer.

check !ipi_desc[i] (as arm does) to avoid the problem.

Signed-off-by: Chen Jun <chenjun102 at huawei.com>
---
 arch/arm64/kernel/smp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 62ed361a4376..3d54f464428b 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -781,6 +781,9 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 	unsigned int cpu, i;
 
 	for (i = 0; i < NR_IPI; i++) {
+		if (!ipi_desc[i])
+			continue;
+
 		seq_printf(p, "%*s%u:%s", prec - 1, "IPI", i,
 			   prec >= 4 ? " " : "");
 		for_each_online_cpu(cpu)
-- 
2.17.1