KASAN: slab-out-of-bounds Read in vcs_scr_readw

KASAN: slab-out-of-bounds Read in vcs_scr_readw

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    596cf45c Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c1d196e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8eb54eee6e6ca4a7
dashboard link: https://syzkaller.appspot.com/bug?extid=7d027845265d531ba506
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c6090ee00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13821b7ae00000

The bug was bisected to:

commit d21b0be246bf3bbf569e6e239f56abb529c7154e
Author: Nicolas Pitre <nicolas.pitre@linaro.org>
Date:   Wed Jun 27 03:56:41 2018 +0000

     vt: introduce unicode mode for /dev/vcs

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1292fbf2e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1192fbf2e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1692fbf2e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7d027845265d531ba506@syzkaller.appspotmail.com
Fixes: d21b0be246bf ("vt: introduce unicode mode for /dev/vcs")

==================================================================
BUG: KASAN: slab-out-of-bounds in vcs_scr_readw+0xc2/0xd0  
drivers/tty/vt/vt.c:4665
Read of size 2 at addr ffff8882192c52c0 by task syz-executor391/9679

CPU: 0 PID: 9679 Comm: syz-executor391 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x197/0x210 lib/dump_stack.c:118
  print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
  __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
  kasan_report+0x12/0x20 mm/kasan/common.c:638
  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:133
  vcs_scr_readw+0xc2/0xd0 drivers/tty/vt/vt.c:4665
  vcs_write+0x646/0xcf0 drivers/tty/vt/vc_screen.c:545
  __vfs_write+0x8a/0x110 fs/read_write.c:494
  vfs_write+0x268/0x5d0 fs/read_write.c:558
  ksys_write+0x14f/0x290 fs/read_write.c:611
  __do_sys_write fs/read_write.c:623 [inline]
  __se_sys_write fs/read_write.c:620 [inline]
  __x64_sys_write+0x73/0xb0 fs/read_write.c:620
  do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x444399
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 7b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe50ca6938 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007ffe50ca6940 RCX: 0000000000444399
RDX: 00000000fffffecb RSI: 0000000020000300 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000400c60
R10: 00007ffe50ca6480 R11: 0000000000000246 R12: 00000000004020a0
R13: 0000000000402130 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 1:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_kmalloc mm/kasan/common.c:512 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:485
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:526
  __do_kmalloc mm/slab.c:3656 [inline]
  __kmalloc+0x163/0x770 mm/slab.c:3665
  kmalloc include/linux/slab.h:561 [inline]
  kzalloc include/linux/slab.h:670 [inline]
  vc_do_resize+0x262/0x1460 drivers/tty/vt/vt.c:1187
  vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
  fbcon_init+0x122d/0x1a90 drivers/video/fbdev/core/fbcon.c:1212
  visual_init+0x30a/0x5e0 drivers/tty/vt/vt.c:1051
  do_bind_con_driver+0x54c/0x8b0 drivers/tty/vt/vt.c:3532
  do_take_over_console+0x449/0x5a0 drivers/tty/vt/vt.c:4113
  do_fbcon_takeover+0x116/0x220 drivers/video/fbdev/core/fbcon.c:581
  fbcon_fb_registered+0x275/0x340 drivers/video/fbdev/core/fbcon.c:3252
  do_register_framebuffer drivers/video/fbdev/core/fbmem.c:1652 [inline]
  register_framebuffer+0x5c3/0xa10 drivers/video/fbdev/core/fbmem.c:1821
  vga16fb_probe+0x711/0x825 drivers/video/fbdev/vga16fb.c:1373
  platform_drv_probe+0x8d/0x140 drivers/base/platform.c:725
  really_probe+0x291/0x710 drivers/base/dd.c:548
  driver_probe_device+0x110/0x220 drivers/base/dd.c:721
  __device_attach_driver+0x1c9/0x230 drivers/base/dd.c:828
  bus_for_each_drv+0x172/0x1f0 drivers/base/bus.c:430
  __device_attach+0x237/0x390 drivers/base/dd.c:894
  device_initial_probe+0x1b/0x20 drivers/base/dd.c:941
  bus_probe_device+0x1f1/0x2a0 drivers/base/bus.c:490
  device_add+0x14fe/0x1d00 drivers/base/core.c:2487
  platform_device_add+0x34d/0x6c0 drivers/base/platform.c:562
  vga16fb_init+0x15f/0x1d6 drivers/video/fbdev/vga16fb.c:1431
  do_one_initcall+0x120/0x81a init/main.c:938
  do_initcall_level init/main.c:1006 [inline]
  do_initcalls init/main.c:1014 [inline]
  do_basic_setup init/main.c:1031 [inline]
  kernel_init_freeable+0x4ca/0x5b9 init/main.c:1191
  kernel_init+0x12/0x1bf init/main.c:1109
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8882192c4000
  which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 4800 bytes inside of
  8192-byte region [ffff8882192c4000, ffff8882192c6000)
The buggy address belongs to the page:
page:ffffea000864b100 refcount:1 mapcount:0 mapping:ffff8880aa4021c0  
index:0x0 compound_mapcount: 0
raw: 057ffe0000010200 ffffea000864ae08 ffffea000863fe08 ffff8880aa4021c0
raw: 0000000000000000 ffff8882192c4000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8882192c5180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffff8882192c5200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8882192c5280: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
                                            ^
  ffff8882192c5300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff8882192c5380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: KASAN: slab-out-of-bounds Read in vcs_scr_readw

[Nicolas Pitre]

On Tue, 3 Dec 2019, syzbot wrote:

> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    596cf45c Merge branch 'akpm' (patches from Andrew)
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14c1d196e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8eb54eee6e6ca4a7
> dashboard link: https://syzkaller.appspot.com/bug?extid=7d027845265d531ba506
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c6090ee00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13821b7ae00000
> 
> The bug was bisected to:
> 
> commit d21b0be246bf3bbf569e6e239f56abb529c7154e
> Author: Nicolas Pitre <nicolas.pitre@linaro.org>
> Date:   Wed Jun 27 03:56:41 2018 +0000
> 
>    vt: introduce unicode mode for /dev/vcs
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1292fbf2e00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1192fbf2e00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1692fbf2e00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+7d027845265d531ba506@syzkaller.appspotmail.com
> Fixes: d21b0be246bf ("vt: introduce unicode mode for /dev/vcs")

This is most likely the same issue that was fixed and queued for 
mainline already. The fix is accessible as commit 0c9acb1af77a in the 
linux-next tree.


Nicolas

Re: KASAN: slab-out-of-bounds Read in vcs_scr_readw

[syzbot]

syzbot suspects this bug was fixed by commit:

commit 0c9acb1af77a3cb8707e43f45b72c95266903cee
Author: Nicolas Pitre <nico@fluxnic.net>
Date:   Tue Nov 5 09:33:16 2019 +0000

     vcs: prevent write access to vcsu devices

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11602fb6e00000
start commit:   76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=7d027845265d531ba506
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17c0459ce00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d4477ae00000

If the result looks correct, please mark the bug fixed by replying with:

#syz fix: vcs: prevent write access to vcsu devices

For information about bisection process see: https://goo.gl/tpsmEJ#bisection