[Qemu-devel] [PATCH] i386: avoid null pointer dereference

[P J P]

   Hello,

A null pointer dereference issue was reported by Mr Ling Liu, CC'd here. It 
occurs while doing I/O port write operations via hmp interface. In that, 
'current_cpu' remains null as it is not called from cpu_exec loop, which 
results in the said issue.

Below is a proposed (tested)patch to fix this issue; Does it look okay?

===
> From ae88a4947fab9a148cd794f8ad2d812e7f5a1d0f Mon Sep 17 00:00:00 2001
From: Prasad J Pandit <address@hidden>
Date: Fri, 18 Dec 2015 11:16:07 +0530
Subject: [PATCH] i386: avoid null pointer dereference

When I/O port write operation is called from hmp interface,
'current_cpu' remains null, as it is not called from cpu_exec()
loop. This leads to a null pointer dereference in vapic_write
routine. Add check to avoid it.

Reported-by: Ling Liu <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
---
 hw/i386/kvmvapic.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
index c6d34b2..18157c7 100644
--- a/hw/i386/kvmvapic.c
+++ b/hw/i386/kvmvapic.c
@@ -634,6 +634,10 @@ static int vapic_prepare(VAPICROMState *s)
 static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
                         unsigned int size)
 {
+    if (!current_cpu) {
+        return;
+    }
+
     CPUState *cs = current_cpu;
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
--
2.4.3
===


Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F