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SubjectKASAN: use-after-free Read in string
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Hello,

syzbot found the following crash on:

HEAD commit: 58c3f14f86c9 Merge tag 'riscv-for-linus-4.19-rc2' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15506dc1400000
kernel config: https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
dashboard link: https://syzkaller.appspot.com/bug?extid=f648cfb7e0b52bf7ae32
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1178aa46400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11735e0a400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f648cfb7e0b52bf7ae32@syzkaller.appspotmail.com

RDX: 0000000000000001 RSI: 0000000000005502 RDI: 0000000000000004
RBP: 00000000006cf018 R08: 0000000000000001 R09: 0000000000000038
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000006
R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
==================================================================
BUG: KASAN: use-after-free in string+0x2c6/0x2d0 lib/vsprintf.c:604
Read of size 1 at addr ffff8801d79c5080 by task syz-executor215/4685

CPU: 1 PID: 4685 Comm: syz-executor215 Not tainted 4.19.0-rc1+ #215
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
string+0x2c6/0x2d0 lib/vsprintf.c:604
vsnprintf+0x48f/0x1b60 lib/vsprintf.c:2293
add_uevent_var+0x140/0x2f0 lib/kobject_uevent.c:659
input_dev_uevent+0x15d/0x860 drivers/input/input.c:1594
dev_uevent+0x340/0x7e0 drivers/base/core.c:1008
kobject_uevent_env+0x45b/0x1110 lib/kobject_uevent.c:547
kobject_uevent+0x1f/0x30 lib/kobject_uevent.c:636
kobject_cleanup lib/kobject.c:649 [inline]
kobject_release lib/kobject.c:691 [inline]
kref_put include/linux/kref.h:70 [inline]
kobject_put+0x1fb/0x280 lib/kobject.c:708
put_device+0x20/0x30 drivers/base/core.c:2024
input_put_device include/linux/input.h:349 [inline]
evdev_free+0x4f/0x70 drivers/input/evdev.c:369
device_release+0x7e/0x210 drivers/base/core.c:891
kobject_cleanup lib/kobject.c:662 [inline]
kobject_release lib/kobject.c:691 [inline]
kref_put include/linux/kref.h:70 [inline]
kobject_put+0x194/0x280 lib/kobject.c:708
cdev_default_release+0x3e/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:70 [inline]
kobject_put+0x194/0x280 lib/kobject.c:708
cdev_put.part.0+0x36/0x50 fs/char_dev.c:368
cdev_put+0x1f/0x30 fs/char_dev.c:366
__fput+0x8ae/0xa40 fs/file_table.c:281
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x1ae4/0x26e0 kernel/exit.c:867
do_group_exit+0x177/0x440 kernel/exit.c:970
__do_sys_exit_group kernel/exit.c:981 [inline]
__se_sys_exit_group kernel/exit.c:979 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:979
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x443a68
Code: Bad RIP value.
RSP: 002b:00007fff70261298 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000443a68
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004c39c8 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d5180 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4685:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc_track_caller+0x14a/0x720 mm/slab.c:3733
kstrndup+0x5f/0xe0 mm/util.c:98
uinput_setup_device_legacy drivers/input/misc/uinput.c:549 [inline]
uinput_write+0x2fb/0x1120 drivers/input/misc/uinput.c:621
__vfs_write+0x117/0x9d0 fs/read_write.c:485
vfs_write+0x1fc/0x560 fs/read_write.c:549
ksys_write+0x101/0x260 fs/read_write.c:598
__do_sys_write fs/read_write.c:610 [inline]
__se_sys_write fs/read_write.c:607 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:607
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 4685:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x210 mm/slab.c:3813
uinput_destroy_device+0xf8/0x250 drivers/input/misc/uinput.c:310
uinput_ioctl_handler.isra.10+0x1439/0x2540 drivers/input/misc/uinput.c:880
uinput_ioctl+0x4c/0x60 drivers/input/misc/uinput.c:1047
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
__do_sys_ioctl fs/ioctl.c:709 [inline]
__se_sys_ioctl fs/ioctl.c:707 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d79c5080
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
32-byte region [ffff8801d79c5080, ffff8801d79c50a0)
The buggy address belongs to the page:
page:ffffea00075e7140 count:1 mapcount:0 mapping:ffff8801dac001c0
index:0xffff8801d79c5fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00075e0908 ffffea00075e7408 ffff8801dac001c0
raw: ffff8801d79c5fc1 ffff8801d79c5000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d79c4f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d79c5000: 00 00 fc fc fc fc fc fc 00 00 00 fc fc fc fc fc
> ffff8801d79c5080: fb fb fb fb fc fc fc fc 07 fc fc fc fc fc fc fc
^
ffff8801d79c5100: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff8801d79c5180: 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.
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