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Message-ID: <20200713110445.553974-1-yangyingliang@huawei.com>
Date: Mon, 13 Jul 2020 11:04:45 +0000
From: Yang Yingliang <yangyingliang@...wei.com>
To: <b.zolnierkie@...sung.com>
CC: <dri-devel@...ts.freedesktop.org>, <linux-fbdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <yangyingliang@...wei.com>
Subject: [PATCH] vgacon: fix a UAF in do_update_region()
I got a UAF report in do_update_region() when I doing fuzz test.
[ 51.161905] BUG: KASAN: use-after-free in do_update_region+0x579/0x600
[ 51.161918] Read of size 2 at addr ffff888000100000 by task test/295
[ 51.161957] CPU: 2 PID: 295 Comm: test Not tainted 5.7.0+ #975
[ 51.161969] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[ 51.161976] Call Trace:
[ 51.162001] dump_stack+0xc6/0x11e
[ 51.162019] ? do_update_region+0x579/0x600
[ 51.162047] print_address_description.constprop.6+0x1a/0x220
[ 51.162083] ? vprintk_func+0x66/0xed
[ 51.162100] ? do_update_region+0x579/0x600
[ 51.162112] ? do_update_region+0x579/0x600
[ 51.162128] kasan_report.cold.9+0x37/0x7c
[ 51.162151] ? do_update_region+0x579/0x600
[ 51.162173] do_update_region+0x579/0x600
[ 51.162207] ? con_get_trans_old+0x230/0x230
[ 51.162229] ? retint_kernel+0x10/0x10
[ 51.162278] csi_J+0x557/0xa00
[ 51.162307] do_con_trol+0x49af/0x5cc0
[ 51.162330] ? lock_downgrade+0x720/0x720
[ 51.162347] ? reset_palette+0x1b0/0x1b0
[ 51.162369] ? lockdep_hardirqs_on_prepare+0x379/0x540
[ 51.162393] ? notifier_call_chain+0x11b/0x160
[ 51.162438] do_con_write.part.24+0xb0a/0x1a30
[ 51.162501] ? do_con_trol+0x5cc0/0x5cc0
[ 51.162522] ? console_unlock+0x7b8/0xb00
[ 51.162555] ? __mutex_unlock_slowpath+0xd4/0x670
[ 51.162574] ? this_tty+0xe0/0xe0
[ 51.162589] ? console_unlock+0x559/0xb00
[ 51.162605] ? wait_for_completion+0x260/0x260
[ 51.162638] con_write+0x31/0xb0
[ 51.162658] n_tty_write+0x4fa/0xd40
[ 51.162710] ? n_tty_read+0x1800/0x1800
[ 51.162730] ? prepare_to_wait_exclusive+0x270/0x270
[ 51.162754] ? __might_fault+0x175/0x1b0
[ 51.162783] tty_write+0x42b/0x8d0
[ 51.162795] ? n_tty_read+0x1800/0x1800
[ 51.162825] ? tty_lookup_driver+0x450/0x450
[ 51.162848] __vfs_write+0x7c/0x100
[ 51.162875] vfs_write+0x1c9/0x510
[ 51.162901] ksys_write+0xff/0x200
[ 51.162918] ? __ia32_sys_read+0xb0/0xb0
[ 51.162940] ? do_syscall_64+0x1a/0x520
[ 51.162957] ? lockdep_hardirqs_on_prepare+0x379/0x540
[ 51.162984] do_syscall_64+0xa1/0x520
[ 51.163008] entry_SYSCALL_64_after_hwframe+0x49/0xb3
After vgacon_set_origin() is called in set_origin(), the vc_origin is
set to vga_vram_base, the vc_pos should between vga_vram_base and
vga_vram_end. But we still use vc_screenbuf_size, if the vga_vram_size
is smaller than vc_screenbuf_size, vc_pos may be out of bound, using it
will cause a use-after-free(or out-of-bounds). Fix this by calling
vc_resize() if vga_vram_size is smaller than vc_screenbuf_size.
Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
---
drivers/video/console/vgacon.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index b51ffb9a208d..2eabb86bb0dd 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1341,6 +1341,9 @@ static int vgacon_set_origin(struct vc_data *c)
if (vga_is_gfx || /* We don't play origin tricks in graphic modes */
(console_blanked && !vga_palette_blanked)) /* Nor we write to blanked screens */
return 0;
+
+ if (c->vc_screenbuf_size > vga_vram_size)
+ vc_resize(c, screen_info.orig_video_cols, screen_info.orig_video_lines);
c->vc_origin = c->vc_visible_origin = vga_vram_base;
vga_set_mem_top(c);
vga_rolled_over = 0;
--
2.25.1
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