syzbot

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BUG: KASAN: null-ptr-deref in atomic_sub_return include/asm-generic/atomic-instrumented.h:159 [inline]
BUG: KASAN: null-ptr-deref in atomic_dec_return include/linux/atomic-fallback.h:455 [inline]
BUG: KASAN: null-ptr-deref in dst_release net/core/dst.c:174 [inline]
BUG: KASAN: null-ptr-deref in dst_release+0x2a/0xb0 net/core/dst.c:169
Write of size 4 at addr 0000000000000334 by task kworker/u4:7/8668

CPU: 0 PID: 8668 Comm: kworker/u4:7 Not tainted 5.2.0-rc3+ #56
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 __kasan_report.cold+0x5/0x40 mm/kasan/report.c:321
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x123/0x190 mm/kasan/generic.c:191
 kasan_check_write+0x14/0x20 mm/kasan/common.c:100
 atomic_sub_return include/asm-generic/atomic-instrumented.h:159 [inline]
 atomic_dec_return include/linux/atomic-fallback.h:455 [inline]
 dst_release net/core/dst.c:174 [inline]
 dst_release+0x2a/0xb0 net/core/dst.c:169
 dst_cache_destroy net/core/dst_cache.c:160 [inline]
 dst_cache_destroy+0xd3/0x1b0 net/core/dst_cache.c:152
 ipip6_dev_free+0x19/0x50 net/ipv6/sit.c:1356
 netdev_run_todo+0x48b/0x7c0 net/core/dev.c:8992
 rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:112
 sit_exit_batch_net+0x565/0x750 net/ipv6/sit.c:1892
 ops_exit_list.isra.0+0xfc/0x150 net/core/net_namespace.c:157
 cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553
 process_one_work+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
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