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Re: [PATCH] hw/display/exynos4210_fimd: Fix potential NULL pointer deref
From: |
AlexChen |
Subject: |
Re: [PATCH] hw/display/exynos4210_fimd: Fix potential NULL pointer dereference |
Date: |
Sat, 31 Oct 2020 10:57:47 +0800 |
User-agent: |
Mozilla/5.0 (Windows NT 6.2; WOW64; rv:17.0) Gecko/20130509 Thunderbird/17.0.6 |
On 2020/10/30 22:28, Peter Maydell wrote:
> On Fri, 30 Oct 2020 at 10:23, AlexChen <alex.chen@huawei.com> wrote:
>>
>> In exynos4210_fimd_update(), the pointer s is dereferenced before
>> being check if it is valid, which may lead to NULL pointer dereference.
>> So move the assignment to global_width after checking that the s is valid
>>
>> Reported-by: Euler Robot <euler.robot@huawei.com>
>> Signed-off-by: Alex Chen <alex.chen@huawei.com>
>> ---
>> hw/display/exynos4210_fimd.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/display/exynos4210_fimd.c b/hw/display/exynos4210_fimd.c
>> index 4c16e1f5a0..a1179d2f89 100644
>> --- a/hw/display/exynos4210_fimd.c
>> +++ b/hw/display/exynos4210_fimd.c
>> @@ -1275,12 +1275,12 @@ static void exynos4210_fimd_update(void *opaque)
>> bool blend = false;
>> uint8_t *host_fb_addr;
>> bool is_dirty = false;
>> - const int global_width = (s->vidtcon[2] & FIMD_VIDTCON2_SIZE_MASK) + 1;
>>
>> if (!s || !s->console || !s->enabled ||
>> surface_bits_per_pixel(qemu_console_surface(s->console)) == 0) {
>> return;
>> }
>> + const int global_width = (s->vidtcon[2] & FIMD_VIDTCON2_SIZE_MASK) + 1;
>> exynos4210_update_resolution(s);
>> surface = qemu_console_surface(s->console);
>
> Yep, this is a bug, but QEMU's coding style doesn't permit
> variable declarations in the middle of functions. You need
> to split the declaration (which stays where it is) and the
> initialization (which can moved down below the !s test.
>
Thans for your review. I have also considered this modification to be
incompatible with
the QEMU's coding style. But the type of global_width is const int which cannot
be
assigned once they are defined.
Could we define the global_width as int, such as this modification:
diff --git a/hw/display/exynos4210_fimd.c b/hw/display/exynos4210_fimd.c
index 4c16e1f5a0..34a960a976 100644
--- a/hw/display/exynos4210_fimd.c
+++ b/hw/display/exynos4210_fimd.c
@@ -1275,12 +1275,14 @@ static void exynos4210_fimd_update(void *opaque)
bool blend = false;
uint8_t *host_fb_addr;
bool is_dirty = false;
- const int global_width = (s->vidtcon[2] & FIMD_VIDTCON2_SIZE_MASK) + 1;
+ int global_width;
if (!s || !s->console || !s->enabled ||
surface_bits_per_pixel(qemu_console_surface(s->console)) == 0) {
return;
}
+
+ global_width = (s->vidtcon[2] & FIMD_VIDTCON2_SIZE_MASK) + 1;
exynos4210_update_resolution(s);
surface = qemu_console_surface(s->console);