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BUG: KASAN: use-after-free in strlen+0x79/0x90 lib/string.c:527
Read of size 1 at addr ffff8881d5400208 by task syz-executor.5/22884

CPU: 1 PID: 22884 Comm: syz-executor.5 Not tainted 5.5.0-rc2-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+0xef/0x16e lib/dump_stack.c:118
 print_address_description.constprop.0+0x16/0x200 mm/kasan/report.c:374
 __kasan_report.cold+0x37/0x7f mm/kasan/report.c:506
 kasan_report+0xe/0x20 mm/kasan/common.c:639
 strlen+0x79/0x90 lib/string.c:527
 strlen include/linux/string.h:302 [inline]
 str_to_user+0x27/0x90 drivers/input/evdev.c:783
 evdev_do_ioctl drivers/input/evdev.c:1186 [inline]
 evdev_ioctl_handler+0x130a/0x19f0 drivers/input/evdev.c:1284
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x90c/0x1420 fs/ioctl.c:732
 ksys_ioctl+0x9b/0xc0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:754
 do_syscall_64+0xb6/0x5c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45af49
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:00007fdd446d8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045af49
RDX: 0000000020000040 RSI: 0000000080404507 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fdd446d96d4
R13: 00000000004c362e R14: 00000000004d96f8 R15: 00000000ffffffff

Allocated by task 1598:
 save_stack+0x1b/0x80 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+0xbf/0xd0 mm/kasan/common.c:486
 kmalloc include/linux/slab.h:556 [inline]
 syslog_print kernel/printk/printk.c:1356 [inline]
 do_syslog kernel/printk/printk.c:1529 [inline]
 do_syslog+0x53b/0x1380 kernel/printk/printk.c:1503
 kmsg_read+0x8a/0xb0 fs/proc/kmsg.c:40
 proc_reg_read+0x1c1/0x280 fs/proc/inode.c:223
 __vfs_read+0x76/0x100 fs/read_write.c:425
 vfs_read+0x1ea/0x430 fs/read_write.c:461
 ksys_read+0x127/0x250 fs/read_write.c:587
 do_syscall_64+0xb6/0x5c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 1598:
 save_stack+0x1b/0x80 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+0x129/0x170 mm/kasan/common.c:474
 slab_free_hook mm/slub.c:1425 [inline]
 slab_free_freelist_hook mm/slub.c:1458 [inline]
 slab_free mm/slub.c:3005 [inline]
 kfree+0xda/0x310 mm/slub.c:3957
 syslog_print kernel/printk/printk.c:1415 [inline]
 do_syslog kernel/printk/printk.c:1529 [inline]
 do_syslog+0x1104/0x1380 kernel/printk/printk.c:1503
 kmsg_read+0x8a/0xb0 fs/proc/kmsg.c:40
 proc_reg_read+0x1c1/0x280 fs/proc/inode.c:223
 __vfs_read+0x76/0x100 fs/read_write.c:425
 vfs_read+0x1ea/0x430 fs/read_write.c:461
 ksys_read+0x127/0x250 fs/read_write.c:587
 do_syscall_64+0xb6/0x5c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881d5400000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 520 bytes inside of
 1024-byte region [ffff8881d5400000, ffff8881d5400400)
The buggy address belongs to the page:
page:ffffea0007550000 refcount:1 mapcount:0 mapping:ffff8881da002280 index:0x0 compound_mapcount: 0
raw: 0200000000010200 ffffea000748f200 0000000200000002 ffff8881da002280
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881d5400100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881d5400180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881d5400200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8881d5400280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881d5400300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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