syzbot has found reproducer for the following crash on upstream commit
c18bb396d3d261ebbb4efbc05129c5d354c541e4 (Tue Apr 10 00:04:10 2018 +0000)
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
syzbot dashboard link: https://syzkaller.appspot.com/bug?extid=7a1cff37dbbef9e7ba4c


So far this crash happened 7 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5445199996125184
syzkaller reproducer: https://syzkaller.appspot.com/x/repro.syz?id=5779667084640256 Raw console output: https://syzkaller.appspot.com/x/log.txt?id=5571293525049344 Kernel config: https://syzkaller.appspot.com/x/.config?id=-771321277174894814
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7a1cff37dbbef9e7b...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed.

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
==================================================================
 fail_dump lib/fault-inject.c:51 [inline]
 should_fail.cold.4+0xa/0x1a lib/fault-inject.c:149
BUG: KASAN: use-after-free in alloc_pid+0x9e8/0xa50 kernel/pid.c:236
Read of size 4 at addr ffff8801ad357898 by task syzkaller392486/4543

 __should_failslab+0x124/0x180 mm/failslab.c:32
 should_failslab+0x9/0x14 mm/slab_common.c:1522
 slab_pre_alloc_hook mm/slab.h:423 [inline]
 slab_alloc mm/slab.c:3378 [inline]
 kmem_cache_alloc+0x2af/0x760 mm/slab.c:3552
 __d_alloc+0xc1/0xc00 fs/dcache.c:1624
 d_alloc+0x8e/0x370 fs/dcache.c:1702
 d_alloc_name+0xb3/0x110 fs/dcache.c:1756
 proc_setup_self+0xbe/0x375 fs/proc/self.c:43
 proc_fill_super+0x24d/0x2f5 fs/proc/inode.c:514
 mount_ns+0x12a/0x1d0 fs/super.c:1036
 proc_mount+0x73/0xa0 fs/proc/root.c:101
 mount_fs+0xae/0x328 fs/super.c:1222
 vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:3303 [inline]
 kern_mount_data+0x50/0xc0 fs/namespace.c:3303
 pid_ns_prepare_proc+0x1e/0x90 fs/proc/root.c:222
 alloc_pid+0x8cf/0xa50 kernel/pid.c:208
 copy_process.part.38+0x36bf/0x6ee0 kernel/fork.c:1809
 copy_process kernel/fork.c:1608 [inline]
 _do_fork+0x291/0x12a0 kernel/fork.c:2089
 SYSC_clone kernel/fork.c:2196 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2190
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x442639
RSP: 002b:00007ffd890f8138 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000442639
RDX: 00000000200008c0 RSI: 0000000020000800 RDI: 000000002000c100
RBP: 00007ffd890f8250 R08: 0000000020000940 R09: 0000000400000000
R10: 0000000020000900 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000001380 R15: 00007ffd890f8278
CPU: 1 PID: 4543 Comm: syzkaller392486 Not tainted 4.16.0+ #17
proc_fill_super: can't allocate /proc/self
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+0xac/0x2f5 mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 alloc_pid+0x9e8/0xa50 kernel/pid.c:236
 copy_process.part.38+0x36bf/0x6ee0 kernel/fork.c:1809
 copy_process kernel/fork.c:1608 [inline]
 _do_fork+0x291/0x12a0 kernel/fork.c:2089
 SYSC_clone kernel/fork.c:2196 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2190
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x442639
RSP: 002b:00007ffd890f8138 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000442639
RDX: 00000000200008c0 RSI: 0000000020000800 RDI: 000000002000c100
RBP: 00007ffd890f8250 R08: 0000000020000940 R09: 0000000000000000
R10: 0000000020000900 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffd890f8278

Allocated by task 4543:
 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
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3554
 kmem_cache_zalloc include/linux/slab.h:691 [inline]
 create_pid_namespace kernel/pid_namespace.c:97 [inline]
 copy_pid_ns+0x2c3/0xb40 kernel/pid_namespace.c:156
 create_new_namespaces+0x48a/0x8f0 kernel/nsproxy.c:94
 copy_namespaces+0x3f7/0x4c0 kernel/nsproxy.c:165
 copy_process.part.38+0x353a/0x6ee0 kernel/fork.c:1798
 copy_process kernel/fork.c:1608 [inline]
 _do_fork+0x291/0x12a0 kernel/fork.c:2089
 SYSC_clone kernel/fork.c:2196 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2190
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 4397:
 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]
 kmem_cache_free+0x86/0x2d0 mm/slab.c:3756
 delayed_free_pidns+0xaa/0xe0 kernel/pid_namespace.c:138
 __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+0x941/0x15f0 kernel/rcu/tree.c:2914
 __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801ad357850
 which belongs to the cache pid_namespace of size 240
The buggy address is located 72 bytes inside of
 240-byte region [ffff8801ad357850, ffff8801ad357940)
The buggy address belongs to the page:
page:ffffea0006b4d5c0 count:1 mapcount:0 mapping:ffff8801ad357000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801ad357000 0000000000000000 000000010000000d
raw: ffffea0007641de0 ffff8801d47f3248 ffff8801d4f030c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801ad357780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801ad357800: 00 00 fc fc fc fc fc fc fc fc fb fb fb fb fb fb
ffff8801ad357880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff8801ad357900: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8801ad357980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

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