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Subjectlinux-next test error: KASAN: use-after-free Write in afs_wake_up_async_call
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Hello,

syzbot found the following crash on:

HEAD commit: 64302eab Add linux-next specific files for 20200613
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17bc9eda100000
kernel config: https://syzkaller.appspot.com/x/.config?x=a4b041729071d963
dashboard link: https://syzkaller.appspot.com/bug?extid=ada89e25a220b3befb36
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ada89e25a220b3befb36@syzkaller.appspotmail.com

tipc: TX() has been purged, node left!
==================================================================
BUG: KASAN: use-after-free in afs_wake_up_async_call+0x6aa/0x770 fs/afs/rxrpc.c:707
Write of size 1 at addr ffff8880940ca9e4 by task kworker/u4:7/6779

CPU: 0 PID: 6779 Comm: kworker/u4:7 Not tainted 5.7.0-next-20200613-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x413 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
afs_wake_up_async_call+0x6aa/0x770 fs/afs/rxrpc.c:707
rxrpc_notify_socket+0x1db/0x5d0 net/rxrpc/recvmsg.c:40
__rxrpc_set_call_completion.part.0+0x172/0x410 net/rxrpc/recvmsg.c:76
__rxrpc_call_completed net/rxrpc/recvmsg.c:112 [inline]
rxrpc_call_completed+0xca/0xf0 net/rxrpc/recvmsg.c:111
rxrpc_discard_prealloc+0x781/0xab0 net/rxrpc/call_accept.c:233
rxrpc_listen+0x147/0x360 net/rxrpc/af_rxrpc.c:245
afs_close_socket+0x95/0x320 fs/afs/rxrpc.c:110
afs_net_exit+0x1bc/0x310 fs/afs/main.c:155
ops_exit_list.isra.0+0xa8/0x150 net/core/net_namespace.c:186
cleanup_net+0x511/0xa50 net/core/net_namespace.c:603
process_one_work+0x965/0x1690 kernel/workqueue.c:2269
worker_thread+0x96/0xe10 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Allocated by task 6836:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc mm/kasan/common.c:494 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:467
kmem_cache_alloc_trace+0x153/0x7d0 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
afs_alloc_call+0x55/0x630 fs/afs/rxrpc.c:141
afs_charge_preallocation+0xe9/0x2d0 fs/afs/rxrpc.c:757
afs_open_socket+0x292/0x360 fs/afs/rxrpc.c:92
afs_net_init+0xa6c/0xe30 fs/afs/main.c:125
ops_init+0xaf/0x420 net/core/net_namespace.c:151
setup_net+0x2de/0x860 net/core/net_namespace.c:341
copy_net_ns+0x293/0x590 net/core/net_namespace.c:482
create_new_namespaces+0x3fb/0xb30 kernel/nsproxy.c:110
unshare_nsproxy_namespaces+0xbd/0x1f0 kernel/nsproxy.c:231
ksys_unshare+0x43d/0x8e0 kernel/fork.c:2983
__do_sys_unshare kernel/fork.c:3051 [inline]
__se_sys_unshare kernel/fork.c:3049 [inline]
__x64_sys_unshare+0x2d/0x40 kernel/fork.c:3049
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 6779:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0xf7/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x109/0x2b0 mm/slab.c:3757
afs_put_call+0x585/0xa40 fs/afs/rxrpc.c:190
rxrpc_discard_prealloc+0x764/0xab0 net/rxrpc/call_accept.c:230
rxrpc_listen+0x147/0x360 net/rxrpc/af_rxrpc.c:245
afs_close_socket+0x95/0x320 fs/afs/rxrpc.c:110
afs_net_exit+0x1bc/0x310 fs/afs/main.c:155
ops_exit_list.isra.0+0xa8/0x150 net/core/net_namespace.c:186
cleanup_net+0x511/0xa50 net/core/net_namespace.c:603
process_one_work+0x965/0x1690 kernel/workqueue.c:2269
worker_thread+0x96/0xe10 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

The buggy address belongs to the object at ffff8880940ca800
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 484 bytes inside of
1024-byte region [ffff8880940ca800, ffff8880940cac00)
The buggy address belongs to the page:
page:ffffea0002503280 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002507e08 ffffea00029a7988 ffff8880aa000c40
raw: 0000000000000000 ffff8880940ca000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880940ca880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880940ca900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880940ca980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880940caa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880940caa80: 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.
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