KASAN: use-after-free Read in cdev

KASAN: use-after-free Read in cdev_put
Status: fixed on 2020/02/12 05:05
Reported-by: syzbot+de5ddcfa2e7edda50ff1@syzkaller.appspotmail.com
Fix commit: 0ce254bc68ed xen-blkback: prevent premature module unload
First crash: 902d, last: 858d

Fix bisection: fixed by (bisect log) :
commit 0ce254bc68edf06f93d3c0271851c619ff729d31
Author: Paul Durrant <pdurrant@amazon.com>
Date: Tue Dec 10 14:53:05 2019 +0000

xen-blkback: prevent premature module unload

similar bugs (2):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	KASAN: use-after-free Read in cdev_put	C		error	4	862d	902d	0/1	upstream: reported C repro on 2019/11/30 06:54
upstream	KASAN: use-after-free Read in cdev_put				6	724d	723d	0/22	auto-closed as invalid on 2020/07/24 11:02

Sample crash report:

input: syz1 as /devices/virtual/input/input7321
input: syz1 as /devices/virtual/input/input7322
input: syz1 as /devices/virtual/input/input7323
input: syz1 as /devices/virtual/input/input7324
==================================================================
BUG: KASAN: use-after-free in cdev_put.part.0+0x4c/0x50 fs/char_dev.c:373
Read of size 8 at addr ffff88808c2f6c28 by task syz-executor062/21631

CPU: 1 PID: 21631 Comm: syz-executor062 Not tainted 4.14.157-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x142/0x197 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 cdev_put.part.0+0x4c/0x50 fs/char_dev.c:373
 cdev_put fs/char_dev.c:372 [inline]
 chrdev_open+0x266/0x590 fs/char_dev.c:431
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3425 [inline]
 path_openat+0x8bd/0x3f70 fs/namei.c:3566
 do_filp_open+0x18e/0x250 fs/namei.c:3600
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x402ec0
RSP: 002b:00007ffc638336c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 000000000000000a RCX: 0000000000402ec0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffc638336e0
RBP: 0000000000000000 R08: 000000000000000f R09: 0000000000000004
R10: 0000000000000004 R11: 0000000000000246 R12: 00000000000004d3
R13: 00007ffc63833cf0 R14: 0000000000000004 R15: 0000000000000000

Allocated by task 21620:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 kmem_cache_alloc_trace+0x152/0x790 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 evdev_connect+0x76/0x4a0 drivers/input/evdev.c:1383
 input_attach_handler+0x154/0x1a0 drivers/input/input.c:1004
 input_register_device.cold+0xbf/0x202 drivers/input/input.c:2161
kobject: 'event5' (ffff8880a037ca38): kobject_uevent_env
 uinput_create_device drivers/input/misc/uinput.c:324 [inline]
 uinput_ioctl_handler.isra.0+0xdc8/0x18a0 drivers/input/misc/uinput.c:839
 uinput_ioctl+0x4a/0x60 drivers/input/misc/uinput.c:1010
kobject: 'event5' (ffff8880a037ca38): fill_kobj_path: path = '/devices/virtual/input/input7320/event5'
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

kobject: '(null)' (ffff8880a037ce68): kobject_cleanup, parent ffff8880a037ca38
Freed by task 21626:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
kobject: '(null)' (ffff8880a037ce68): calling ktype release
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcc/0x270 mm/slab.c:3815
 evdev_free+0x5e/0x70 drivers/input/evdev.c:364
 device_release+0x7b/0x1a0 drivers/base/core.c:821
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put.cold+0x269/0x2f9 lib/kobject.c:692
kobject: 'input7325' (ffff88809974d7a0): kobject_add_internal: parent: 'input', set: 'devices'
 cdev_default_release+0x41/0x50 fs/char_dev.c:613
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put.cold+0x269/0x2f9 lib/kobject.c:692
 cdev_put.part.0+0x39/0x50 fs/char_dev.c:374
 cdev_put fs/char_dev.c:372 [inline]
 chrdev_open+0x266/0x590 fs/char_dev.c:431
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3425 [inline]
 path_openat+0x8bd/0x3f70 fs/namei.c:3566
 do_filp_open+0x18e/0x250 fs/namei.c:3600
kobject: 'input7325' (ffff88809974d7a0): kobject_uevent_env
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88808c2f6640
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1512 bytes inside of
 2048-byte region [ffff88808c2f6640, ffff88808c2f6e40)
The buggy address belongs to the page:
page:ffffea000230bd80 count:1 mapcount:0 mapping:ffff88808c2f6640 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff88808c2f6640 0000000000000000 0000000100000003
kobject: 'input7325' (ffff88809974d7a0): fill_kobj_path: path = '/devices/virtual/input/input7325'
raw: ffffea00022fbb20 ffffea0002038ba0 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808c2f6b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88808c2f6b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88808c2f6c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88808c2f6c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
kobject: 'input7325' (ffff88809974d7a0): fill_kobj_path: path = '/devices/virtual/input/input7325'
 ffff88808c2f6d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (6):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci2-linux-4-14	2019/12/02 09:52	linux-4.14.y	fbc5fe7a54d0	f879db37	.config	log	report	syz	C
ci2-linux-4-14	2019/12/02 05:10	linux-4.14.y	fbc5fe7a54d0	f879db37	.config	log	report	syz	C
ci2-linux-4-14	2019/11/30 05:55	linux-4.14.y	43598c571e7e	3a75be00	.config	log	report	syz	C
ci2-linux-4-14	2019/12/13 10:50	linux-4.14.y	a844dc4c5442	2a752b7c	.config	log	report
ci2-linux-4-14	2019/12/10 18:09	linux-4.14.y	a844dc4c5442	4b83c8fb	.config	log	report
ci2-linux-4-14	2019/12/07 16:51	linux-4.14.y	a844dc4c5442	85f26751	.config	log	report