On 30. 07. 20, 15:24, Yang Yingliang wrote:
>
> On 2020/7/30 19:04, Jiri Slaby wrote:
>> On 13. 07. 20, 12:57, Yang Yingliang wrote:
>>> I got a slab-out-of-bounds report when I doing fuzz test.
>>>
>>> [ 334.989515]
>>> ==================================================================
>>> [ 334.989577] BUG: KASAN: slab-out-of-bounds in
>>> vgacon_scroll+0x57a/0x8ed
>>> [ 334.989588] Write of size 1766 at addr ffff8883de69ff3e by task
>>> test/2658
>>> [ 334.989593]
>>> [ 334.989608] CPU: 3 PID: 2658 Comm: test Not tainted
>>> 5.7.0-rc5-00005-g152036d1379f #789
>>> [ 334.989617] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>>> BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
>>> [ 334.989624] Call Trace:
>>> [ 334.989646] dump_stack+0xe4/0x14e
>>> [ 334.989676] print_address_description.constprop.5+0x3f/0x60
>>> [ 334.989699] ? vgacon_scroll+0x57a/0x8ed
>>> [ 334.989710] __kasan_report.cold.8+0x92/0xaf
>>> [ 334.989735] ? vgacon_scroll+0x57a/0x8ed
>>> [ 334.989761] kasan_report+0x37/0x50
>>> [ 334.989789] check_memory_region+0x1c1/0x1e0
>>> [ 334.989806] memcpy+0x38/0x60
>>> [ 334.989824] vgacon_scroll+0x57a/0x8ed
>>> [ 334.989876] con_scroll+0x4ef/0x5e0
>> ...
>>> Because vgacon_scrollback_cur->tail plus memcpy size is greater than
>>> vgacon_scrollback_cur->size. Fix this by checking the memcpy size.
>>>
>>> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
>>> Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
>>> ---
>>> drivers/video/console/vgacon.c | 11 ++++++++---
>>> 1 file changed, 8 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/video/console/vgacon.c
>>> b/drivers/video/console/vgacon.c
>>> index 998b0de1812f..b51ffb9a208d 100644
>>> --- a/drivers/video/console/vgacon.c
>>> +++ b/drivers/video/console/vgacon.c
>>> @@ -243,6 +243,7 @@ static void vgacon_scrollback_startup(void)
>>> static void vgacon_scrollback_update(struct vc_data *c, int t, int
>>> count)
>>> {
>>> void *p;
>>> + int size;
>>> if (!vgacon_scrollback_cur->data ||
>>> !vgacon_scrollback_cur->size ||
>>> c->vc_num != fg_console)
>>> @@ -251,13 +252,17 @@ static void vgacon_scrollback_update(struct
>>> vc_data *c, int t, int count)
>>> p = (void *) (c->vc_origin + t * c->vc_size_row);
>>> while (count--) {
>>> + size = vgacon_scrollback_cur->size -
>>> vgacon_scrollback_cur->tail;
>>> + if (size > c->vc_size_row)
>>> + size = c->vc_size_row;
>>> +
>>> scr_memcpyw(vgacon_scrollback_cur->data +
>>> vgacon_scrollback_cur->tail,
>>> - p, c->vc_size_row);
>>> + p, size);
>> Are you sure the consumer can handle split lines? As vgacon_scrolldelta
>> (soff in particular) looks to me like it doesn't.
>>
>> Have you tested you patch? I mean with soft scrollback on the vga
>> console?
>
> I only test the patch with the reproduce program.
Out of curiosity, what is it doing? Resize and then scroll by \n (line
feed)? Can you share it?
thanks,
--
js
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