Re: KASAN: use-after-free Read in add_uevent_var

[Daniel Vetter <daniel@ffwll.ch>]

On Sat, May 04, 2019 at 11:16:05AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    a4ccb5f9 Merge tag 'drm-fixes-2019-05-03' of git://anongit..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1205d570a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2bd0da4b8de0b004
> dashboard link: https://syzkaller.appspot.com/bug?extid=6da9575ba2db4da91831
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1769f62ca00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=167ae984a00000
> 
> The bug was bisected to:
> 
> commit 0a1c7959acd9674a0e4e59f911f3e5fbf25fd693
> Author: Wolfram Sang <wsa@the-dreams.de>
> Date:   Wed May 17 15:22:18 2017 +0000
> 
>     gpu: drm: tc35876x: move header file out of I2C realm

Bisect seems to have gone off the rails. No idea where or why.
-Daniel

> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=138fe12ca00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=104fe12ca00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=178fe12ca00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+6da9575ba2db4da91831@syzkaller.appspotmail.com
> Fixes: 0a1c7959acd9 ("gpu: drm: tc35876x: move header file out of I2C
> realm")
> 
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000005502
> RDX: 0000000000000000 RSI: 00000000080daf20 RDI: 00000000080f0f84
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> ==================================================================
> BUG: KASAN: use-after-free in string+0x208/0x230 lib/vsprintf.c:606
> Read of size 1 at addr ffff8880a55aa200 by task syz-executor222/7839
> 
> CPU: 1 PID: 7839 Comm: syz-executor222 Not tainted 5.1.0-rc7+ #98
> 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+0x172/0x1f0 lib/dump_stack.c:113
>  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
>  kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:129
>  string+0x208/0x230 lib/vsprintf.c:606
>  vsnprintf+0xbfc/0x1af0 lib/vsprintf.c:2396
>  add_uevent_var+0x14d/0x310 lib/kobject_uevent.c:661
>  input_dev_uevent+0x163/0x890 drivers/input/input.c:1594
>  dev_uevent+0x312/0x580 drivers/base/core.c:1180
>  kobject_uevent_env+0x487/0x1030 lib/kobject_uevent.c:549
>  kobject_uevent+0x20/0x26 lib/kobject_uevent.c:638
>  kobject_cleanup lib/kobject.c:649 [inline]
>  kobject_release lib/kobject.c:691 [inline]
>  kref_put include/linux/kref.h:67 [inline]
>  kobject_put.cold+0x177/0x2ec lib/kobject.c:708
>  put_device+0x20/0x30 drivers/base/core.c:2205
>  input_put_device include/linux/input.h:349 [inline]
>  evdev_free+0x51/0x70 drivers/input/evdev.c:369
>  device_release+0x7d/0x210 drivers/base/core.c:1064
>  kobject_cleanup lib/kobject.c:662 [inline]
>  kobject_release lib/kobject.c:691 [inline]
>  kref_put include/linux/kref.h:67 [inline]
>  kobject_put.cold+0x28f/0x2ec lib/kobject.c:708
>  cdev_default_release+0x41/0x50 fs/char_dev.c:607
>  kobject_cleanup lib/kobject.c:662 [inline]
>  kobject_release lib/kobject.c:691 [inline]
>  kref_put include/linux/kref.h:67 [inline]
>  kobject_put.cold+0x28f/0x2ec lib/kobject.c:708
>  cdev_put.part.0+0x39/0x50 fs/char_dev.c:368
>  cdev_put+0x20/0x30 fs/char_dev.c:366
>  __fput+0x6df/0x8d0 fs/file_table.c:281
>  ____fput+0x16/0x20 fs/file_table.c:309
>  task_work_run+0x14a/0x1c0 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x90a/0x2fa0 kernel/exit.c:876
>  do_group_exit+0x135/0x370 kernel/exit.c:980
>  __do_sys_exit_group kernel/exit.c:991 [inline]
>  __se_sys_exit_group kernel/exit.c:989 [inline]
>  __ia32_sys_exit_group+0x44/0x50 kernel/exit.c:989
>  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
>  do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
> RIP: 0023:0xf7ff7849
> Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90
> 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90
> 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
> RSP: 002b:00000000fff2db8c EFLAGS: 00000292 ORIG_RAX: 00000000000000fc
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000080f1298
> RDX: 0000000000000000 RSI: 00000000080daf1c RDI: 00000000080f12a0
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 7839:
>  save_stack+0x45/0xd0 mm/kasan/common.c:75
>  set_track mm/kasan/common.c:87 [inline]
>  __kasan_kmalloc mm/kasan/common.c:497 [inline]
>  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
>  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511
>  __do_kmalloc mm/slab.c:3727 [inline]
>  __kmalloc_track_caller+0x158/0x740 mm/slab.c:3742
>  kstrndup+0x5f/0xf0 mm/util.c:96
>  uinput_dev_setup+0x1d4/0x310 drivers/input/misc/uinput.c:475
>  uinput_ioctl_handler.isra.0+0x12b8/0x1cc0 drivers/input/misc/uinput.c:886
>  uinput_compat_ioctl+0x70/0x90 drivers/input/misc/uinput.c:1062
>  __do_compat_sys_ioctl fs/compat_ioctl.c:1052 [inline]
>  __se_compat_sys_ioctl fs/compat_ioctl.c:998 [inline]
>  __ia32_compat_sys_ioctl+0x197/0x620 fs/compat_ioctl.c:998
>  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
>  do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
> 
> Freed by task 7839:
>  save_stack+0x45/0xd0 mm/kasan/common.c:75
>  set_track mm/kasan/common.c:87 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
>  kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
>  __cache_free mm/slab.c:3499 [inline]
>  kfree+0xcf/0x230 mm/slab.c:3822
>  uinput_destroy_device+0xf8/0x250 drivers/input/misc/uinput.c:311
>  uinput_ioctl_handler.isra.0+0x886/0x1cc0 drivers/input/misc/uinput.c:882
>  uinput_compat_ioctl+0x70/0x90 drivers/input/misc/uinput.c:1062
>  __do_compat_sys_ioctl fs/compat_ioctl.c:1052 [inline]
>  __se_compat_sys_ioctl fs/compat_ioctl.c:998 [inline]
>  __ia32_compat_sys_ioctl+0x197/0x620 fs/compat_ioctl.c:998
>  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
>  do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
> 
> The buggy address belongs to the object at ffff8880a55aa200
>  which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 0 bytes inside of
>  32-byte region [ffff8880a55aa200, ffff8880a55aa220)
> The buggy address belongs to the page:
> page:ffffea0002956a80 count:1 mapcount:0 mapping:ffff8880aa4001c0
> index:0xffff8880a55aafc1
> flags: 0x1fffc0000000200(slab)
> raw: 01fffc0000000200 ffffea0002949e88 ffffea00029482c8 ffff8880aa4001c0
> raw: ffff8880a55aafc1 ffff8880a55aa000 0000000100000039 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880a55aa100: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>  ffff8880a55aa180: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> > ffff8880a55aa200: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>                    ^
>  ffff8880a55aa280: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>  ffff8880a55aa300: fb fb fb fb fc fc fc fc fb fb fb fb 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.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 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
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch