bisecting fixing commit since b850307b279cbd12ab8c654d1a3dfe55319cc475
building syzkaller on eabcced43245881efa7769d938bcaf795ed48742
testing commit b850307b279cbd12ab8c654d1a3dfe55319cc475 with gcc (GCC) 8.4.1 20210217
kernel signature: cdadfc3b0525ccf5270129627f2114ef98a7eaf25e5e3d4dab4b1c7d432ea854
run #0: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #1: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #2: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #3: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #4: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #5: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #6: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #7: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #8: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #9: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #10: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #11: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #12: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #13: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #14: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #15: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #16: OK
run #17: OK
run #18: OK
run #19: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
testing current HEAD 3242aa3a635c0958671ee1e4b0958dcc7c4e5c79
testing commit 3242aa3a635c0958671ee1e4b0958dcc7c4e5c79 with gcc (GCC) 8.4.1 20210217
kernel signature: dcc687288e55e0067be8203fa4d7203962ee2e44e60853a40083bd1322c1eb27
run #0: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #1: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #2: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #3: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #4: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #5: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #6: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #7: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #8: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #9: OK
revisions tested: 2, total time: 33m52.026809714s (build: 15m10.164718741s, test: 17m38.837033697s)
the crash still happens on HEAD
commit msg: Linux 4.14.222
crash: KASAN: use-after-free Read in __ext4_check_dir_entry
IPv6: ADDRCONF(NETDEV_UP): batadv_slave_0: link is not ready
batman_adv: batadv0: Interface activated: batadv_slave_0
IPv6: ADDRCONF(NETDEV_UP): veth0_vlan: link is not ready
==================================================================
IPv6: ADDRCONF(NETDEV_UP): vlan0: link is not ready
BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x2c6/0x3f0 fs/ext4/dir.c:82
Read of size 1 at addr ffff8881da5df001 by task syz-executor.3/7078

CPU: 1 PID: 7078 Comm: syz-executor.3 Not tainted 4.14.222-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x14b/0x1e7 lib/dump_stack.c:58
 print_address_description.cold.6+0x9/0x1ca mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold.7+0x11a/0x2d3 mm/kasan/report.c:393
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:427
 __ext4_check_dir_entry+0x2c6/0x3f0 fs/ext4/dir.c:82
 ext4_readdir+0x72a/0x3010 fs/ext4/dir.c:240
 iterate_dir+0x188/0x660 fs/readdir.c:52
 SYSC_getdents fs/readdir.c:269 [inline]
 SyS_getdents+0x111/0x1d0 fs/readdir.c:250
 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x464599
RSP: 002b:00007f898c34e198 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000464599
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00000000004f5b60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000055bf00
R13: 00007f898c34e6bc R14: 00000000ffffffff R15: 0000000000000003

The buggy address belongs to the page:
page:ffffea00076977c0 count:0 mapcount:-127 mapping:          (null) index:0x0
flags: 0x17ffe0000000000()
raw: 017ffe0000000000 0000000000000000 0000000000000000 00000000ffffff80
raw: ffff88823fff9e80 ffff88823fff9e80 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881da5def00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881da5def80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881da5df000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8881da5df080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881da5df100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================