BUG: unable to handle kernel NULL pointer dereference in generic_perform_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 3bd837bf Linux 4.19.59
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=157a8e58600000
kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2f3bc2e9ff5d4
dashboard link: https://syzkaller.appspot.com/bug?extid=e591a7e12363b67e450a
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e591a7...@syzkaller.appspotmail.com

binder: 17242:17243 ioctl 4018620d 20000100 returned -22
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 97435067 P4D 97435067 PUD a573a067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 17243 Comm: syz-executor.4 Not tainted 4.19.59 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff88805859f9f0 EFLAGS: 00010246
RAX: ffffffff875ab400 RBX: 0000000000000000 RCX: 0000000000001000
RDX: 0000000000000000 RSI: ffff888094acc570 RDI: ffff8880a68a7580
RBP: ffff88805859fb08 R08: 0000000000000000 R09: ffff88805859fa80
R10: ffffed1015d24732 R11: ffff8880ae923993 R12: 0000000000001000
R13: ffff88805859fae0 R14: ffff88805859fd48 R15: ffff888094acc570
FS: 00007ffac97f1700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000084bbb000 CR4: 00000000001406e0
Call Trace:
generic_perform_write+0x22a/0x520 /mm/filemap.c:3139
__generic_file_write_iter+0x25e/0x630 /mm/filemap.c:3264
ext4_file_write_iter+0x32b/0x1060 /fs/ext4/file.c:266
call_write_iter /./include/linux/fs.h:1820 [inline]
new_sync_write /fs/read_write.c:474 [inline]
__vfs_write+0x587/0x810 /fs/read_write.c:487
vfs_write+0x20c/0x560 /fs/read_write.c:549
ksys_write+0x14f/0x2d0 /fs/read_write.c:599
__do_sys_write /fs/read_write.c:611 [inline]
__se_sys_write /fs/read_write.c:608 [inline]
__x64_sys_write+0x73/0xb0 /fs/read_write.c:608
do_syscall_64+0xfd/0x620 /arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459819
Code: fd b7 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 b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffac97f0c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459819
RDX: 000000000000ff4a RSI: 0000000020000100 RDI: 0000000000000007
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffac97f16d4
R13: 00000000004c9796 R14: 00000000004e0ba0 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000000
kobject: 'loop5' (000000007ab946ac): kobject_uevent_env
kobject: 'loop5' (000000007ab946ac): fill_kobj_path: path
= '/devices/virtual/block/loop5'
---[ end trace ca16ac926346d8fa ]---
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff88805859f9f0 EFLAGS: 00010246
RAX: ffffffff875ab400 RBX: 0000000000000000 RCX: 0000000000001000
RDX: 0000000000000000 RSI: ffff888094acc570 RDI: ffff8880a68a7580
RBP: ffff88805859fb08 R08: 0000000000000000 R09: ffff88805859fa80
kobject: 'loop3' (00000000537e5140): kobject_uevent_env
kobject: 'loop3' (00000000537e5140): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop5' (000000007ab946ac): kobject_uevent_env
R10: ffffed1015d24732 R11: ffff8880ae923993 R12: 0000000000001000
kobject: 'loop5' (000000007ab946ac): fill_kobj_path: path
= '/devices/virtual/block/loop5'
R13: ffff88805859fae0 R14: ffff88805859fd48 R15: ffff888094acc570
FS: 00007ffac97f1700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ff6b36000 CR3: 0000000084bbb000 CR4: 00000000001406f0


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.