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Date: Thu, 30 Jul 2020 13:04:17 +0200 From: Jiri Slaby <jirislaby@...nel.org> To: Yang Yingliang <yangyingliang@...wei.com>, b.zolnierkie@...sung.com Cc: dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org, 张云海 <zhangyunhai@...ocus.com> Subject: Re: [PATCH] vgacon: Fix an out-of-bounds in vgacon_scrollback_update() 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@...wei.com> > Signed-off-by: Yang Yingliang <yangyingliang@...wei.com> > --- > 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? > vgacon_scrollback_cur->cnt++; > - p += c->vc_size_row; > - vgacon_scrollback_cur->tail += c->vc_size_row; > + p += size; > + vgacon_scrollback_cur->tail += size; > > if (vgacon_scrollback_cur->tail >= vgacon_scrollback_cur->size) > vgacon_scrollback_cur->tail = 0; > thanks, -- js suse labs
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