BUG: unable to handle kernel NULL pointer dereference in __do_softirq

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4cb967a3d9d9 selftests/bpf: fix file resource leak
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15a82ba1400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2c8e578694e13f29
dashboard link: https://syzkaller.appspot.com/bug?extid=6528c946c37ba2809d0a
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127664f6400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6528c9...@syzkaller.appspotmail.com

device nr0 entered promiscuous mode
device nr0 entered promiscuous mode
device nr0 entered promiscuous mode
device nr0 entered promiscuous mode
device nr0 entered promiscuous mode
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 1d3a54067 P4D 1d3a54067 PUD 1ba78a067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 10511 Comm: syz-executor4 Not tainted 4.19.0-rc7+ #125
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff8801daf07868 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff860a27bf
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffff8801ab2bd298
RBP: ffff8801daf07df8 R08: ffff8801c7b2e140 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff8801daf07dd0 R15: ffff8801ab2bd298
FS: 00007f851cacc700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000001bc908000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
__do_softirq+0x30b/0xad8 kernel/softirq.c:292
do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1047
</IRQ>
do_softirq.part.13+0x126/0x160 kernel/softirq.c:336
do_softirq kernel/softirq.c:328 [inline]
__local_bh_enable_ip+0x21d/0x260 kernel/softirq.c:189
local_bh_enable include/linux/bottom_half.h:32 [inline]
tun_get_user+0x1c0b/0x4250 drivers/net/tun.c:1963
tun_chr_write_iter+0xb9/0x160 drivers/net/tun.c:1993
call_write_iter include/linux/fs.h:1808 [inline]
new_sync_write fs/read_write.c:474 [inline]
__vfs_write+0x6b8/0x9f0 fs/read_write.c:487
vfs_write+0x1fc/0x560 fs/read_write.c:549
ksys_write+0x101/0x260 fs/read_write.c:598
__do_sys_write fs/read_write.c:610 [inline]
__se_sys_write fs/read_write.c:607 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:607
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f851cacbc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
RDX: 000000000000017b RSI: 0000000020000000 RDI: 000000000000000e
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f851cacc6d4
R13: 00000000004c5560 R14: 00000000004d8e98 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000000
---[ end trace 108e300304238a6e ]---
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff8801daf07868 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff860a27bf
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffff8801ab2bd298
RBP: ffff8801daf07df8 R08: ffff8801c7b2e140 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff8801daf07dd0 R15: ffff8801ab2bd298
FS: 00007f851cacc700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000001bc908000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[Eric Biggers]

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Probably stale.

#syz invalid