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SubjectRe: KASAN: use-after-free Read in rxrpc_send_keepalive
From
syzbot has found a reproducer for the following crash on:

HEAD commit: ed2393ca Add linux-next specific files for 20190827
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=156adb1e600000
kernel config: https://syzkaller.appspot.com/x/.config?x=2ef5940a07ed45f4
dashboard link: https://syzkaller.appspot.com/bug?extid=d850c266e3df14da1d31
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=167ab582600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d850c266e3df14da1d31@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
==================================================================
BUG: KASAN: use-after-free in rxrpc_send_keepalive+0x8a2/0x940
net/rxrpc/output.c:634
Read of size 8 at addr ffff888086b01218 by task kworker/0:1/12

CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.3.0-rc6-next-20190827 #74
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: krxrpcd rxrpc_peer_keepalive_worker
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
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
rxrpc_send_keepalive+0x8a2/0x940 net/rxrpc/output.c:634
rxrpc_peer_keepalive_dispatch net/rxrpc/peer_event.c:369 [inline]
rxrpc_peer_keepalive_worker+0x7be/0xd02 net/rxrpc/peer_event.c:430
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 8741:
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 mm/slab.c:3655 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3664
kmalloc_array include/linux/slab.h:614 [inline]
kcalloc include/linux/slab.h:625 [inline]
alloc_pipe_info+0x199/0x420 fs/pipe.c:676
get_pipe_inode fs/pipe.c:738 [inline]
create_pipe_files+0x8e/0x730 fs/pipe.c:770
__do_pipe_flags+0x48/0x250 fs/pipe.c:807
do_pipe2+0x84/0x160 fs/pipe.c:855
__do_sys_pipe2 fs/pipe.c:873 [inline]
__se_sys_pipe2 fs/pipe.c:871 [inline]
__x64_sys_pipe2+0x54/0x80 fs/pipe.c:871
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8741:
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
free_pipe_info+0x243/0x300 fs/pipe.c:709
put_pipe_info+0xd0/0xf0 fs/pipe.c:582
pipe_release+0x1e6/0x280 fs/pipe.c:603
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
do_syscall_64+0x65f/0x760 arch/x86/entry/common.c:300
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888086b01200
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 24 bytes inside of
1024-byte region [ffff888086b01200, ffff888086b01600)
The buggy address belongs to the page:
page:ffffea00021ac000 refcount:1 mapcount:0 mapping:ffff8880aa400c40
index:0xffff888086b00480 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00027b5588 ffffea00028e3808 ffff8880aa400c40
raw: ffff888086b00480 ffff888086b00000 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888086b01100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888086b01180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888086b01200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888086b01280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888086b01300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

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