Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

A reproducer is attached.
You may need to run it a few times.

On commit 9c763584b7c8911106bb77af7e648bef09af9d80 (4.9-rc6, Nov 20).

==================================================================
BUG: KASAN: use-after-free in bcm_rx_thr_flush+0x284/0x2b0
Read of size 1 at addr ffff88006c1faae5 by task a.out/3874

page:ffffea0001b07e80 count:1 mapcount:0 mapping:          (null) index:0x0
flags: 0x100000000000080(slab)
page dumped because: kasan: bad access detected

CPU: 1 PID: 3874 Comm: a.out Not tainted 4.9.0-rc6+ #427
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 ffff88006ab07900 ffffffff81b472e4 ffff88006ab07990 ffff88006c1faae5
 00000000000000fa 00000000000000fb ffff88006ab07980 ffffffff8150ad42
 ffff88006323ce58 0000000000000246 ffff880068ca8000 0000000000000282
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff81b472e4>] dump_stack+0xb3/0x10f lib/dump_stack.c:51
 [<     inline     >] describe_address mm/kasan/report.c:259
 [<ffffffff8150ad42>] kasan_report_error+0x122/0x560 mm/kasan/report.c:365
 [<     inline     >] kasan_report mm/kasan/report.c:387
 [<ffffffff8150b1be>] __asan_report_load1_noabort+0x3e/0x40
mm/kasan/report.c:405
 [<     inline     >] bcm_rx_do_flush net/can/bcm.c:589
 [<ffffffff83577e04>] bcm_rx_thr_flush+0x284/0x2b0 net/can/bcm.c:612
 [<     inline     >] bcm_rx_setup net/can/bcm.c:1199
 [<ffffffff83578b36>] bcm_sendmsg+0xbb6/0x30e0 net/can/bcm.c:1351
 [<     inline     >] sock_sendmsg_nosec net/socket.c:621
 [<ffffffff82b7176c>] sock_sendmsg+0xcc/0x110 net/socket.c:631
 [<ffffffff82b73651>] ___sys_sendmsg+0x771/0x8b0 net/socket.c:1954
 [<ffffffff82b7563e>] __sys_sendmsg+0xce/0x170 net/socket.c:1988
 [<     inline     >] SYSC_sendmsg net/socket.c:1999
 [<ffffffff82b7570d>] SyS_sendmsg+0x2d/0x50 net/socket.c:1995
 [<ffffffff83fc4301>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209

The buggy address belongs to the object at ffff88006c1faae0
 which belongs to the cache kmalloc-32 of size 32
The buggy address ffff88006c1faae5 is located 5 bytes inside
 of 32-byte region [ffff88006c1faae0, ffff88006c1fab00)

Freed by task 2013:
 [<ffffffff8107e236>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 [<ffffffff81509e56>] save_stack+0x46/0xd0 mm/kasan/kasan.c:495
 [<     inline     >] set_track mm/kasan/kasan.c:507
 [<ffffffff8150a6b3>] kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:571
 [<     inline     >] slab_free_hook mm/slub.c:1352
 [<     inline     >] slab_free_freelist_hook mm/slub.c:1374
 [<     inline     >] slab_free mm/slub.c:2951
 [<ffffffff81506b98>] kfree+0xe8/0x2b0 mm/slub.c:3871
 [<ffffffff819dd8c1>] selinux_cred_free+0x51/0x80 security/selinux/hooks.c:3725
 [<ffffffff819ce358>] security_cred_free+0x48/0x80 security/security.c:907
 [<ffffffff8117e27d>] put_cred_rcu+0xed/0x390 kernel/cred.c:116
 [<     inline     >] __rcu_reclaim kernel/rcu/rcu.h:118
 [<     inline     >] rcu_do_batch kernel/rcu/tree.c:2776
 [<     inline     >] invoke_rcu_callbacks kernel/rcu/tree.c:3040
 [<     inline     >] __rcu_process_callbacks kernel/rcu/tree.c:3007
 [<ffffffff8125dfe0>] rcu_process_callbacks+0xa40/0x1190 kernel/rcu/tree.c:3024
 [<ffffffff83fc70af>] __do_softirq+0x23f/0x8e5 kernel/softirq.c:284

Allocated by task 1826:
 [<ffffffff8107e236>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 [<ffffffff81509e56>] save_stack+0x46/0xd0 mm/kasan/kasan.c:495
 [<     inline     >] set_track mm/kasan/kasan.c:507
 [<ffffffff8150a0cb>] kasan_kmalloc+0xab/0xe0 mm/kasan/kasan.c:598
 [<ffffffff8150a632>] kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:537
 [<     inline     >] slab_post_alloc_hook mm/slab.h:417
 [<     inline     >] slab_alloc_node mm/slub.c:2708
 [<     inline     >] slab_alloc mm/slub.c:2716
 [<ffffffff815090ef>] __kmalloc_track_caller+0xcf/0x2a0 mm/slub.c:4240
 [<ffffffff8146bf84>] kmemdup+0x24/0x50 mm/util.c:113
 [<ffffffff819dcbe9>] selinux_cred_prepare+0x49/0xb0
security/selinux/hooks.c:3739
 [<ffffffff819ce40d>] security_prepare_creds+0x7d/0xb0 security/security.c:912
 [<ffffffff8117fab3>] prepare_creds+0x243/0x340 kernel/cred.c:277
 [<ffffffff81181bab>] copy_creds+0x7b/0x5c0 kernel/cred.c:343
 [<ffffffff81109c6e>] copy_process.part.45+0x86e/0x5b50 kernel/fork.c:1529
 [<     inline     >] copy_process kernel/fork.c:1479
 [<ffffffff8110f2fa>] _do_fork+0x1ba/0xcc0 kernel/fork.c:1933
 [<     inline     >] SYSC_clone kernel/fork.c:2043
 [<ffffffff8110fed7>] SyS_clone+0x37/0x50 kernel/fork.c:2037
 [<ffffffff81006465>] do_syscall_64+0x195/0x490 arch/x86/entry/common.c:280
 [<ffffffff83fc43c9>] return_from_SYSCALL_64+0x0/0x7a
arch/x86/entry/entry_64.S:251

Memory state around the buggy address:
 ffff88006c1fa980: fc fc fb fb fb fb fc fc fb fb fb fb fc fc fb fb
 ffff88006c1faa00: fb fb fc fc fb fb fb fb fc fc fb fb fb fb fc fc

ffff88006c1faa80: fb fb fb fb fc fc fb fb fb fb fc fc fb fb fb fb

                                                       ^
 ffff88006c1fab00: fc fc fb fb fb fb fc fc 00 00 00 00 fc fc 00 00
 ffff88006c1fab80: 00 00 fc fc fb fb fb fb fc fc fb fb fb fb fc fc
==================================================================

Thanks!