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SubjectKASAN: use-after-free Read in j1939_tp_txtimer
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Hello,

syzbot found the following crash on:

HEAD commit: 46cf053e Linux 5.5-rc3
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=158ac866e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
dashboard link: https://syzkaller.appspot.com/bug?extid=5322482fe520b02aea30
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11af21fee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=116b4ec1e00000

The bug was bisected to:

commit 9d71dd0c70099914fcd063135da3c580865e924c
Author: The j1939 authors <linux-can@vger.kernel.org>
Date: Mon Oct 8 09:48:36 2018 +0000

can: add support of SAE J1939 protocol

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=124d0ac1e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=114d0ac1e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=164d0ac1e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5322482fe520b02aea30@syzkaller.appspotmail.com
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")

==================================================================
BUG: KASAN: use-after-free in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: use-after-free in j1939_session_tx_dat
net/can/j1939/transport.c:790 [inline]
BUG: KASAN: use-after-free in j1939_xtp_txnext_transmiter
net/can/j1939/transport.c:847 [inline]
BUG: KASAN: use-after-free in j1939_tp_txtimer+0x777/0x1b00
net/can/j1939/transport.c:1095
Read of size 7 at addr ffff88809073d917 by task ksoftirqd/0/9

CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.5.0-rc3-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:639
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
memcpy+0x24/0x50 mm/kasan/common.c:125
memcpy include/linux/string.h:380 [inline]
j1939_session_tx_dat net/can/j1939/transport.c:790 [inline]
j1939_xtp_txnext_transmiter net/can/j1939/transport.c:847 [inline]
j1939_tp_txtimer+0x777/0x1b00 net/can/j1939/transport.c:1095
__run_hrtimer kernel/time/hrtimer.c:1517 [inline]
__hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1579
hrtimer_run_softirq+0x17e/0x270 kernel/time/hrtimer.c:1596
__do_softirq+0x262/0x98c kernel/softirq.c:292
run_ksoftirqd kernel/softirq.c:603 [inline]
run_ksoftirqd+0x8e/0x110 kernel/softirq.c:595
smpboot_thread_fn+0x6a3/0xa40 kernel/smpboot.c:165
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 16:
save_stack+0x23/0x90 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+0xcf/0xe0 mm/kasan/common.c:486
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:521
slab_post_alloc_hook mm/slab.h:584 [inline]
slab_alloc_node mm/slab.c:3263 [inline]
kmem_cache_alloc_node+0x138/0x740 mm/slab.c:3575
__alloc_skb+0xd5/0x5e0 net/core/skbuff.c:197
alloc_skb include/linux/skbuff.h:1049 [inline]
j1939_tp_tx_dat_new+0x38/0x530 net/can/j1939/transport.c:568
j1939_tp_tx_dat net/can/j1939/transport.c:606 [inline]
j1939_session_tx_dat net/can/j1939/transport.c:791 [inline]
j1939_xtp_txnext_transmiter net/can/j1939/transport.c:847 [inline]
j1939_tp_txtimer+0x7a7/0x1b00 net/can/j1939/transport.c:1095
__run_hrtimer kernel/time/hrtimer.c:1517 [inline]
__hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1579
hrtimer_run_softirq+0x17e/0x270 kernel/time/hrtimer.c:1596
__do_softirq+0x262/0x98c kernel/softirq.c:292

Freed by task 16:
save_stack+0x23/0x90 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+0x102/0x150 mm/kasan/common.c:474
kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
__cache_free mm/slab.c:3426 [inline]
kmem_cache_free+0x86/0x320 mm/slab.c:3694
kfree_skbmem net/core/skbuff.c:623 [inline]
kfree_skbmem+0xfb/0x1c0 net/core/skbuff.c:617
__kfree_skb net/core/skbuff.c:680 [inline]
consume_skb net/core/skbuff.c:838 [inline]
consume_skb+0x103/0x410 net/core/skbuff.c:832
vcan_tx+0x29f/0x7f0 drivers/net/can/vcan.c:110
__netdev_start_xmit include/linux/netdevice.h:4447 [inline]
netdev_start_xmit include/linux/netdevice.h:4461 [inline]
xmit_one net/core/dev.c:3420 [inline]
dev_hard_start_xmit+0x1a3/0x9b0 net/core/dev.c:3436
__dev_queue_xmit+0x2b05/0x35c0 net/core/dev.c:4013
dev_queue_xmit+0x18/0x20 net/core/dev.c:4046
can_send+0x439/0x890 net/can/af_can.c:277
j1939_send_one+0x29d/0x360 net/can/j1939/main.c:340
j1939_tp_tx_dat net/can/j1939/transport.c:615 [inline]
j1939_session_tx_dat net/can/j1939/transport.c:791 [inline]
j1939_xtp_txnext_transmiter net/can/j1939/transport.c:847 [inline]
j1939_tp_txtimer+0x5a9/0x1b00 net/can/j1939/transport.c:1095
__run_hrtimer kernel/time/hrtimer.c:1517 [inline]
__hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1579
hrtimer_run_softirq+0x17e/0x270 kernel/time/hrtimer.c:1596
__do_softirq+0x262/0x98c kernel/softirq.c:292

The buggy address belongs to the object at ffff88809073d840
which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 215 bytes inside of
224-byte region [ffff88809073d840, ffff88809073d920)
The buggy address belongs to the page:
page:ffffea000241cf40 refcount:1 mapcount:0 mapping:ffff88821b774e00
index:0x0
raw: 00fffe0000000200 ffffea00026df588 ffffea00023d9308 ffff88821b774e00
raw: 0000000000000000 ffff88809073d0c0 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809073d800: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff88809073d880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809073d900: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88809073d980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809073da00: fb fb fb fb fb fb fb fb 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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