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KASAN: use-after-free Read in fbcon_cursor

Status: fixed on 2020/09/25 01:17
Subsystems: fbdev
[Documentation on labels]
Reported-by: syzbot+9116ecc1978ca3a12f43@syzkaller.appspotmail.com
Fix commit: f8d1653daec0 vt: defer kfree() of vc_screenbuf in vc_do_resize()
First crash: 1804d, last: 1559d
Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: KASAN: use-after-free Read in fbcon_putcs (log)
Repro: syz .config
  
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Discussions (9)
Title Replies (including bot) Last reply
[PATCH 4.19 000/125] 4.19.143-rc1 review 147 (147) 2020/10/26 00:54
[PATCH 4.4 00/62] 4.4.235-rc1 review 70 (70) 2020/09/30 09:01
[PATCH 5.8 000/255] 5.8.6-rc1 review 263 (263) 2020/09/03 09:29
[PATCH 4.14 00/91] 4.14.196-rc1 review 95 (95) 2020/09/02 16:46
[PATCH 4.9 00/78] 4.9.235-rc1 review 82 (82) 2020/09/02 16:46
[PATCH 5.4 000/214] 5.4.62-rc1 review 219 (219) 2020/09/02 07:24
[PATCH] vt: defer kfree() of vc_screenbuf in vc_do_resize() 5 (5) 2020/08/11 15:10
Re: KASAN: use-after-free Read in fbcon_cursor 1 (1) 2019/12/16 11:03
KASAN: use-after-free Read in fbcon_cursor 0 (1) 2019/12/15 20:35
▶ ▼ Similar bugs (2)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.14 KASAN: use-after-free Read in fbcon_cursor syz inconclusive 3 1627d 1804d 0/1 upstream: reported syz repro on 2019/12/15 04:16
linux-4.19 KASAN: use-after-free Read in fbcon_cursor syz done 4 1544d 1804d 1/1 fixed on 2020/09/30 06:27
▶ ▼ Fix bisection attempts (3)
Created Duration User Patch Repo Result
2020/06/13 00:19 0m (2) bisect fix upstream error job log
2020/04/11 08:53 19m bisect fix upstream OK (0) job log log
2020/01/28 02:33 21m bisect fix upstream OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in fbcon_cursor+0x4ef/0x660 drivers/video/fbdev/core/fbcon.c:1380
Read of size 2 at addr ffff8880959ff0cc by task syz-executor.0/10203

CPU: 1 PID: 10203 Comm: syz-executor.0 Not tainted 5.5.0-rc1-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:639
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:133
 fbcon_cursor+0x4ef/0x660 drivers/video/fbdev/core/fbcon.c:1380
 fbcon_scrolldelta+0x679/0x1220 drivers/video/fbdev/core/fbcon.c:2877
 fbcon_set_origin+0x43/0x50 drivers/video/fbdev/core/fbcon.c:2928
 set_origin+0xf3/0x400 drivers/tty/vt/vt.c:919
 vc_do_resize+0xacc/0x1460 drivers/tty/vt/vt.c:1264
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a909
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f1a84ca0c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a909
RDX: 0000000020000000 RSI: 0000000000005609 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1a84ca16d4
R13: 00000000004c7009 R14: 00000000004dd670 R15: 00000000ffffffff

Allocated by task 9734:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
 __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
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 10203:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:335 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 vc_do_resize+0xa69/0x1460 drivers/tty/vt/vt.c:1261
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 vt_ioctl+0x14bb/0x26d0 drivers/tty/vt/vt_ioctl.c:840
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880959ff0c0
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 12 bytes inside of
 32-byte region [ffff8880959ff0c0, ffff8880959ff0e0)
The buggy address belongs to the page:
page:ffffea0002567fc0 refcount:1 mapcount:0 mapping:ffff8880aa4001c0 index:0xffff8880959fffc1
raw: 00fffe0000000200 ffffea00027c7748 ffffea000276ee08 ffff8880aa4001c0
raw: ffff8880959fffc1 ffff8880959ff000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880959fef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880959ff000: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff8880959ff080: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                                              ^
 ffff8880959ff100: 00 01 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8880959ff180: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================

Crashes (10):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2019/12/15 07:04 upstream 07c4b9e9f71a eef6e580 .config console log report syz ci-upstream-kasan-gce-selinux-root
2019/12/15 05:47 upstream 07c4b9e9f71a eef6e580 .config console log report syz ci-upstream-kasan-gce-root
2019/12/25 14:54 linux-next 7ddd09fc4b74 be5c2c81 .config console log report syz ci-upstream-linux-next-kasan-gce-root
2020/08/16 02:53 upstream c9c9735c46f5 424dd8e7 .config console log report ci-upstream-kasan-gce-selinux-root
2020/08/03 10:19 upstream 5a30a78924ec 196277c4 .config console log report ci-upstream-kasan-gce-smack-root
2020/05/14 00:19 upstream 24085f70a6e1 a885920d .config console log report ci-upstream-kasan-gce-smack-root
2020/05/03 15:23 upstream f66ed1ebbfde 58ae5e18 .config console log report ci-upstream-kasan-gce-smack-root
2020/04/23 19:42 upstream c578ddb39e56 2e44d63e .config console log report ci-upstream-kasan-gce-selinux-root
2020/08/15 01:42 upstream b923f1247b72 424dd8e7 .config console log report ci-upstream-kasan-gce-386
2020/03/12 05:19 linux-next 770fbb32d34e e7caca8e .config console log report ci-upstream-linux-next-kasan-gce-root
* Struck through repros no longer work on HEAD.