KASAN: slab-out-of-bounds Read in rxrpc_send_keepalive

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 089cf7f6 Linux 5.3-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=138924d6600000
kernel config: https://syzkaller.appspot.com/x/.config?x=b89bb446a3faaba4
dashboard link: https://syzkaller.appspot.com/bug?extid=9793cab84a94fab264ea
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [da...@davemloft.net dhow...@redhat.com
linu...@lists.infradead.org linux-...@vger.kernel.org
net...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9793ca...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in rxrpc_send_keepalive+0x8a2/0x940
net/rxrpc/output.c:634
Read of size 8 at addr ffff8880a97f4058 by task kworker/1:0/17407

CPU: 1 PID: 17407 Comm: kworker/1:0 Not tainted 5.3.0-rc7 #0
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.cold+0xd4/0x306 mm/kasan/report.c:351
__kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
kasan_report+0x12/0x17 mm/kasan/common.c:618
__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 9731:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:493 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:466
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:501
slab_post_alloc_hook mm/slab.h:520 [inline]
slab_alloc mm/slab.c:3319 [inline]
kmem_cache_alloc+0x121/0x710 mm/slab.c:3483
getname_flags fs/namei.c:138 [inline]
getname_flags+0xd6/0x5b0 fs/namei.c:128
getname+0x1a/0x20 fs/namei.c:209
do_sys_open+0x2c9/0x5d0 fs/open.c:1083
__do_sys_open fs/open.c:1107 [inline]
__se_sys_open fs/open.c:1102 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1102
do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9731:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:455
kasan_slab_free+0xe/0x10 mm/kasan/common.c:463
__cache_free mm/slab.c:3425 [inline]
kmem_cache_free+0x86/0x320 mm/slab.c:3693
putname+0xef/0x130 fs/namei.c:259
do_sys_open+0x318/0x5d0 fs/open.c:1098
__do_sys_open fs/open.c:1107 [inline]
__se_sys_open fs/open.c:1102 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1102
do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a97f4640
which belongs to the cache names_cache of size 4096
The buggy address is located 1512 bytes to the left of
4096-byte region [ffff8880a97f4640, ffff8880a97f5640)
The buggy address belongs to the page:
page:ffffea0002a5fd00 refcount:1 mapcount:0 mapping:ffff88821bc46380
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0001740d88 ffffea00014bff08 ffff88821bc46380
raw: 0000000000000000 ffff8880a97f4640 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a97f3f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a97f3f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a97f4000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880a97f4080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a97f4100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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[syzbot]

> net/rxrpc/output.c:634

> #syz dup: KASAN: use-after-free Read in rxrpc_send_keepalive

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