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BUG: KASAN: use-after-free in atomic_dec_return include/asm-generic/atomic-instrumented.h:198 [inline]
BUG: KASAN: use-after-free in dst_release+0x27/0xa0 net/core/dst.c:185
Write of size 4 at addr ffff8801b1a9d240 by task syz-executor3/12446

CPU: 0 PID: 12446 Comm: syz-executor3 Not tainted 4.16.0+ #288
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1a7/0x27d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23c/0x360 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 atomic_dec_return include/asm-generic/atomic-instrumented.h:198 [inline]
 dst_release+0x27/0xa0 net/core/dst.c:185
 sk_dst_set include/net/sock.h:1812 [inline]
 sk_dst_reset include/net/sock.h:1824 [inline]
 sock_setbindtodevice net/core/sock.c:610 [inline]
 sock_setsockopt+0x431/0x1b20 net/core/sock.c:707
 compat_sock_setsockopt net/compat.c:383 [inline]
 __compat_sys_setsockopt+0x37d/0x710 net/compat.c:400
 C_SYSC_setsockopt net/compat.c:416 [inline]
 compat_SyS_setsockopt+0x34/0x50 net/compat.c:413
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f06c99
RSP: 002b:00000000f5f020ac EFLAGS: 00000282 ORIG_RAX: 000000000000016e
RAX: ffffffffffffffda RBX: 0000000000000014 RCX: 0000000000000001
RDX: 0000000000000019 RSI: 0000000020000000 RDI: 0000000000000010
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 12446:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3542
 dst_alloc+0x11f/0x1a0 net/core/dst.c:104
 rt_dst_alloc+0xe9/0x540 net/ipv4/route.c:1520
 __mkroute_output net/ipv4/route.c:2265 [inline]
 ip_route_output_key_hash_rcu+0xa49/0x2c60 net/ipv4/route.c:2493
 ip_route_output_key_hash+0x20b/0x370 net/ipv4/route.c:2322
 __ip_route_output_key include/net/route.h:126 [inline]
 ip_route_output_flow+0x26/0xa0 net/ipv4/route.c:2577
 ip_route_output_ports include/net/route.h:163 [inline]
 pptp_connect+0xa84/0x1170 drivers/net/ppp/pptp.c:453
 __sys_connect+0x213/0x4a0 net/socket.c:1664
 SYSC_connect net/socket.c:1675 [inline]
 SyS_connect+0x24/0x30 net/socket.c:1672
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 12438:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3486 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3744
 dst_destroy+0x266/0x380 net/core/dst.c:140
 dst_destroy_rcu+0x16/0x20 net/core/dst.c:153
 __rcu_reclaim kernel/rcu/rcu.h:178 [inline]
 rcu_do_batch kernel/rcu/tree.c:2675 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
 rcu_process_callbacks+0xd6c/0x17b0 kernel/rcu/tree.c:2914
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801b1a9d200
 which belongs to the cache ip_dst_cache of size 168
The buggy address is located 64 bytes inside of
 168-byte region [ffff8801b1a9d200, ffff8801b1a9d2a8)
The buggy address belongs to the page:
page:ffffea0006c6a740 count:1 mapcount:0 mapping:ffff8801b1a9d000 index:0xffff8801b1a9df00
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801b1a9d000 ffff8801b1a9df00 0000000100000003
raw: ffff8801d67c6638 ffffea0006b3d460 ffff8801d4ef4800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b1a9d100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b1a9d180: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
>ffff8801b1a9d200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff8801b1a9d280: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b1a9d300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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