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 Yingliangyangyingliang@huawei.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 998b0de..2ee3d62 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1336,6 +1336,9 @@ 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;