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SubjectKASAN: use-after-free Read in slcan_open
From
Hello,

syzbot found the following crash on:

HEAD commit: 32ef9553 Merge tag 'fsnotify_for_v5.5-rc1' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12a48e9ce00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff560c3de405258c
dashboard link: https://syzkaller.appspot.com/bug?extid=b5ec6fd05ab552a78532
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12943882e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10562f86e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b5ec6fd05ab552a78532@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in slc_sync drivers/net/can/slcan.c:504 [inline]
BUG: KASAN: use-after-free in slcan_open+0x8a1/0x9e0
drivers/net/can/slcan.c:579
Read of size 8 at addr ffff88809a6e0b88 by task syz-executor961/9030

CPU: 1 PID: 9030 Comm: syz-executor961 Not tainted 5.4.0-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:634
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
slc_sync drivers/net/can/slcan.c:504 [inline]
slcan_open+0x8a1/0x9e0 drivers/net/can/slcan.c:579
tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:469
tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:596
tiocsetd drivers/tty/tty_io.c:2334 [inline]
tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2594
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4429e9
Code: e8 dc 02 03 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 1b 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc7db87168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004429e9
RDX: 00000000200000c0 RSI: 0000000000005423 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000003031
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000004 R14: 00007ffc7db871dc R15: 0000000000000000

Allocated by task 9029:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
__do_kmalloc_node mm/slab.c:3615 [inline]
__kmalloc_node+0x4e/0x70 mm/slab.c:3622
kmalloc_node include/linux/slab.h:599 [inline]
kvmalloc_node+0xbd/0x100 mm/util.c:564
kvmalloc include/linux/mm.h:670 [inline]
kvzalloc include/linux/mm.h:678 [inline]
alloc_netdev_mqs+0x98/0xde0 net/core/dev.c:9730
slc_alloc drivers/net/can/slcan.c:533 [inline]
slcan_open+0x32d/0x9e0 drivers/net/can/slcan.c:590
tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:469
tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:596
tiocsetd drivers/tty/tty_io.c:2334 [inline]
tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2594
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9029:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
kasan_set_free_info mm/kasan/common.c:332 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:471
kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
__cache_free mm/slab.c:3425 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3756
kvfree+0x61/0x70 mm/util.c:593
netdev_freemem net/core/dev.c:9684 [inline]
free_netdev+0x3c0/0x470 net/core/dev.c:9839
slcan_open+0x848/0x9e0 drivers/net/can/slcan.c:620
tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:469
tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:596
tiocsetd drivers/tty/tty_io.c:2334 [inline]
tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2594
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
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 ffff88809a6e0000
which belongs to the cache kmalloc-32k of size 32768
The buggy address is located 2952 bytes inside of
32768-byte region [ffff88809a6e0000, ffff88809a6e8000)
The buggy address belongs to the page:
page:ffffea000269b800 refcount:1 mapcount:0 mapping:ffff8880aa402540
index:0x0 compound_mapcount: 0
raw: 00fffe0000010200 ffffea000244d008 ffff8880aa401d48 ffff8880aa402540
raw: 0000000000000000 ffff88809a6e0000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809a6e0a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809a6e0b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809a6e0b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809a6e0c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809a6e0c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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