KASAN: use-after-free Read in __dev_map_entry_free

[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=15ad7d10400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa9c20c48788d1c1
dashboard link: https://syzkaller.appspot.com/bug?extid=457d3e2ffbcf31aee5c0
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1195225f800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=171a7ce4400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+457d3e2ffbcf31aee5c0@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in dev_map_flush_old kernel/bpf/devmap.c:365  
[inline]
BUG: KASAN: use-after-free in __dev_map_entry_free+0x2a8/0x300  
kernel/bpf/devmap.c:379
Read of size 8 at addr ffff8801b8da38c8 by task ksoftirqd/1/18

CPU: 1 PID: 18 Comm: ksoftirqd/1 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
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 dev_map_flush_old kernel/bpf/devmap.c:365 [inline]
 __dev_map_entry_free+0x2a8/0x300 kernel/bpf/devmap.c:379
 __rcu_reclaim kernel/rcu/rcu.h:178 [inline]
 rcu_do_batch kernel/rcu/tree.c:2558 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2818 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2785 [inline]
 rcu_process_callbacks+0xe9d/0x1760 kernel/rcu/tree.c:2802
 __do_softirq+0x2e0/0xaf5 kernel/softirq.c:284
 run_ksoftirqd+0x86/0x100 kernel/softirq.c:645
 smpboot_thread_fn+0x417/0x870 kernel/smpboot.c:164
 kthread+0x345/0x410 kernel/kthread.c:240
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

Allocated by task 6675:
 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]
 dev_map_alloc+0x208/0x7f0 kernel/bpf/devmap.c:102
 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 26:
 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
 dev_map_free+0x4fa/0x670 kernel/bpf/devmap.c:191
 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 ffff8801b8da37c0
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 264 bytes inside of
 512-byte region [ffff8801b8da37c0, ffff8801b8da39c0)
The buggy address belongs to the page:
page:ffffea0006e368c0 count:1 mapcount:0 mapping:ffff8801da800940  
index:0xffff8801b8da3540
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0007217b88 ffffea0006e30cc8 ffff8801da800940
raw: ffff8801b8da3540 ffff8801b8da3040 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b8da3780: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8801b8da3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801b8da3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8801b8da3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b8da3980: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


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