KASAN: use-after-free Write in free_htab_elem

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f0dc7f9c6dd9 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11dad428400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa9c20c48788d1c1
dashboard link: https://syzkaller.appspot.com/bug?extid=ce67d3e4fa77eedee964
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

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+ce67d3e4fa77eedee964@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in atomic_dec  
include/asm-generic/atomic-instrumented.h:114 [inline]
BUG: KASAN: use-after-free in free_htab_elem+0x23/0x40  
kernel/bpf/sockmap.c:224
Write of size 4 at addr ffff8801b3dce648 by task syz-executor1/8114

CPU: 0 PID: 8114 Comm: syz-executor1 Not tainted 4.17.0+ #39
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 atomic_dec include/asm-generic/atomic-instrumented.h:114 [inline]
 free_htab_elem+0x23/0x40 kernel/bpf/sockmap.c:224
 bpf_tcp_close+0x8c1/0xf80 kernel/bpf/sockmap.c:273
 inet_release+0x104/0x1f0 net/ipv4/af_inet.c:427
 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:459
 __sock_release+0xd7/0x260 net/socket.c:603
 sock_close+0x19/0x20 net/socket.c:1186
 __fput+0x353/0x890 fs/file_table.c:209
 ____fput+0x15/0x20 fs/file_table.c:243
 task_work_run+0x1e4/0x290 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x1aee/0x2730 kernel/exit.c:865
 do_group_exit+0x16f/0x430 kernel/exit.c:968
 get_signal+0x886/0x1960 kernel/signal.c:2468
 do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
 exit_to_usermode_loop+0x2cf/0x360 arch/x86/entry/common.c:162
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6ac/0x800 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455b29
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f3bbf323ce8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000072bf78 RCX: 0000000000455b29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000072bf78
RBP: 000000000072bf78 R08: 0000000000000000 R09: 000000000072bf50
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd7addc2cf R14: 00007f3bbf3249c0 R15: 0000000000000001

Allocated by task 8104:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
 kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
 kmalloc include/linux/slab.h:513 [inline]
 kzalloc include/linux/slab.h:706 [inline]
 sock_hash_alloc+0x20d/0x6a0 kernel/bpf/sockmap.c:2003
 find_and_alloc_map kernel/bpf/syscall.c:129 [inline]
 map_create+0x393/0x1010 kernel/bpf/syscall.c:453
 __do_sys_bpf kernel/bpf/syscall.c:2351 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:2328 [inline]
 __x64_sys_bpf+0x303/0x510 kernel/bpf/syscall.c:2328
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 2131:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kfree+0xd9/0x260 mm/slab.c:3813
 sock_hash_free+0x51c/0x6e0 kernel/bpf/sockmap.c:2098
 bpf_map_free_deferred+0xba/0xf0 kernel/bpf/syscall.c:262
 process_one_work+0xc64/0x1b70 kernel/workqueue.c:2153
 worker_thread+0x181/0x13a0 kernel/workqueue.c:2296
 kthread+0x345/0x410 kernel/kthread.c:240
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

The buggy address belongs to the object at ffff8801b3dce540
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 264 bytes inside of
 512-byte region [ffff8801b3dce540, ffff8801b3dce740)
The buggy address belongs to the page:
page:ffffea0006cf7380 count:1 mapcount:0 mapping:ffff8801da800940 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006caccc8 ffffea0006f57b08 ffff8801da800940
raw: 0000000000000000 ffff8801b3dce040 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b3dce500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8801b3dce580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801b3dce600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8801b3dce680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b3dce700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.