bisecting fixing commit since fdc072324f3c66190a20f57490b4842a391d8233
building syzkaller on 58da4c35b15200b7279f18ea15bc8644618aae78
testing commit fdc072324f3c66190a20f57490b4842a391d8233 with gcc (GCC) 8.1.0
kernel signature: 618f079767a546f4f0d65322b0d476c985d3196fe8030737a181b917ae40619d
all runs: crashed: KASAN: use-after-free Write in get_block
testing current HEAD c14d30dc9987047b439b03d6e6db7d54d9f7f180
testing commit c14d30dc9987047b439b03d6e6db7d54d9f7f180 with gcc (GCC) 8.1.0
kernel signature: 6d8c9185453c373c55689d9a7d344c87d1eefae2fdb7062e084f745c49e9cf9f
all runs: crashed: KASAN: use-after-free Write in get_block
revisions tested: 2, total time: 26m59.607006745s (build: 19m26.674229297s, test: 6m6.62010511s)
the crash still happens on HEAD
commit msg: Linux 4.19.139
crash: KASAN: use-after-free Write in get_block
Process accounting resumed
Process accounting resumed
Process accounting resumed
Process accounting resumed
==================================================================
BUG: KASAN: use-after-free in alloc_branch fs/minix/itree_common.c:92 [inline]
BUG: KASAN: use-after-free in get_block+0xf30/0x1120 fs/minix/itree_common.c:191
Write of size 2 at addr ffff8880765dcba4 by task syz-executor.4/6616

CPU: 1 PID: 6616 Comm: syz-executor.4 Not tainted 4.19.139-syzkaller #0
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+0x123/0x177 lib/dump_stack.c:118
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 __asan_report_store2_noabort+0x17/0x20 mm/kasan/report.c:436
 alloc_branch fs/minix/itree_common.c:92 [inline]
 get_block+0xf30/0x1120 fs/minix/itree_common.c:191
 V1_minix_get_block+0x9/0x10 fs/minix/itree_v1.c:56
 minix_get_block+0xa7/0x110 fs/minix/inode.c:379
 __block_write_begin_int+0x39b/0x1a80 fs/buffer.c:1978
 __block_write_begin fs/buffer.c:2028 [inline]
 block_write_begin+0x48/0x260 fs/buffer.c:2087
 minix_write_begin+0x2f/0xc0 fs/minix/inode.c:415
 generic_perform_write+0x289/0x480 mm/filemap.c:3162
 __generic_file_write_iter+0x201/0x580 mm/filemap.c:3287
 generic_file_write_iter+0x29f/0x650 mm/filemap.c:3315
 call_write_iter include/linux/fs.h:1821 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x443/0x890 fs/read_write.c:487
 __kernel_write+0xe4/0x350 fs/read_write.c:506
 do_acct_process+0xa74/0xed0 kernel/acct.c:520
 acct_pin_kill+0x29/0x100 kernel/acct.c:174
 pin_kill+0x140/0x640 fs/fs_pin.c:50
 mnt_pin_kill+0x51/0x130 fs/fs_pin.c:87
 cleanup_mnt+0xff/0x130 fs/namespace.c:1095
 __cleanup_mnt+0xd/0x10 fs/namespace.c:1105
 task_work_run+0x108/0x180 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:193 [inline]
 exit_to_usermode_loop+0x1a9/0x200 arch/x86/entry/common.c:167
 prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
 do_syscall_64+0x413/0x4e0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45f2d7
Code: 64 89 04 25 d0 02 00 00 58 5f ff d0 48 89 c7 e8 8f be ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 2d 8c fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff604699f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000045f2d7
RDX: 0000000000402ff8 RSI: 0000000000000002 RDI: 00007fff60469aa0
RBP: 000000000000000b R08: 0000000000000000 R09: 0000000000000009
R10: 0000000000000005 R11: 0000000000000246 R12: 00007fff6046ab30
R13: 000000000198f940 R14: 0000000000000000 R15: 00007fff6046ab30

The buggy address belongs to the page:
page:ffffea0001d97700 count:0 mapcount:0 mapping:0000000000000000 index:0x1
flags: 0xfffe0000000000()
raw: 00fffe0000000000 ffffea0001d97048 ffff8880aeb2fc48 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880765dca80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880765dcb00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880765dcb80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff8880765dcc00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880765dcc80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
MINIX-fs: mounting unchecked file system, running fsck is recommended