KASAN: use-after-free Read in bcm_can_tx

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cbfa1702 Linux 4.14.198
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10de8ffb900000
kernel config: https://syzkaller.appspot.com/x/.config?x=3990958d85b55e59
dashboard link: https://syzkaller.appspot.com/bug?extid=5ca851459ed04c778d1d
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13db511b900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=161ca100500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5ca851...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in bcm_can_tx+0x4dc/0x5f0 net/can/bcm.c:312
Read of size 4 at addr ffff88809d6a6a50 by task ksoftirqd/0/7

CPU: 0 PID: 7 Comm: ksoftirqd/0 Not tainted 4.14.198-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+0x1b2/0x283 lib/dump_stack.c:58
print_address_description.cold+0x54/0x1d3 mm/kasan/report.c:252
kasan_report_error.cold+0x8a/0x194 mm/kasan/report.c:351
kasan_report mm/kasan/report.c:409 [inline]
__asan_report_load4_noabort+0x68/0x70 mm/kasan/report.c:429
bcm_can_tx+0x4dc/0x5f0 net/can/bcm.c:312
bcm_tx_timeout_tsklet+0x174/0x2a0 net/can/bcm.c:422
tasklet_action+0x195/0x340 kernel/softirq.c:513
__do_softirq+0x254/0xa1d kernel/softirq.c:288
run_ksoftirqd+0x50/0x1a0 kernel/softirq.c:670
smpboot_thread_fn+0x5c1/0x920 kernel/smpboot.c:164
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Allocated by task 8519:
save_stack mm/kasan/kasan.c:447 [inline]
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xeb/0x160 mm/kasan/kasan.c:551
kmem_cache_alloc_trace+0x131/0x3d0 mm/slab.c:3618
kmalloc include/linux/slab.h:488 [inline]
kzalloc include/linux/slab.h:661 [inline]
bcm_tx_setup net/can/bcm.c:952 [inline]
bcm_sendmsg+0x2029/0x3a10 net/can/bcm.c:1388
sock_sendmsg_nosec net/socket.c:646 [inline]
sock_sendmsg+0xb5/0x100 net/socket.c:656
___sys_sendmsg+0x6c8/0x800 net/socket.c:2062
__sys_sendmsg+0xa3/0x120 net/socket.c:2096
SYSC_sendmsg net/socket.c:2107 [inline]
SyS_sendmsg+0x27/0x40 net/socket.c:2103
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

Freed by task 8519:
save_stack mm/kasan/kasan.c:447 [inline]
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0xc3/0x1a0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3496 [inline]
kfree+0xc9/0x250 mm/slab.c:3815
bcm_release+0xff/0x6c0 net/can/bcm.c:1540
__sock_release+0xcd/0x2b0 net/socket.c:602
sock_close+0x15/0x20 net/socket.c:1139
__fput+0x25f/0x7a0 fs/file_table.c:210
task_work_run+0x11f/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x46/0xbb

The buggy address belongs to the object at ffff88809d6a6900
which belongs to the cache kmalloc-1024 of size 1024
The buggy address is located 336 bytes inside of
1024-byte region [ffff88809d6a6900, ffff88809d6a6d00)
The buggy address belongs to the page:
page:ffffea000275a980 count:1 mapcount:0 mapping:ffff88809d6a6000 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff88809d6a6000 0000000000000000 0000000100000007
raw: ffffea0002184620 ffffea000270fe20 ffff88812fe50ac0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809d6a6900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809d6a6980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809d6a6a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809d6a6a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809d6a6b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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