bisecting fixing commit since b850307b279cbd12ab8c654d1a3dfe55319cc475
building syzkaller on eabcced43245881efa7769d938bcaf795ed48742
testing commit b850307b279cbd12ab8c654d1a3dfe55319cc475 with gcc (GCC) 8.1.0
kernel signature: 78d7f07609a55db491364a6c207b2eb551b22546ea86233b5d46a3bcecae03fd
run #0: crashed: KASAN: use-after-free 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: slab-out-of-bounds Read in __ext4_check_dir_entry
run #8: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #9: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
testing current HEAD 3f2ecb86cb909da0b9157fd2952ad79924cbe5ae
testing commit 3f2ecb86cb909da0b9157fd2952ad79924cbe5ae with gcc (GCC) 8.1.0
kernel signature: 9b01f3bd8158f0750a1d8b341a78c539f4469d7c4df6b376b162e18943c60ab7
run #0: crashed: KASAN: slab-out-of-bounds Read in __ext4_check_dir_entry
run #1: crashed: KASAN: use-after-free 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: use-after-free Read in __ext4_check_dir_entry
run #5: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #6: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #7: crashed: KASAN: use-after-free Read in __ext4_check_dir_entry
run #8: OK
run #9: OK
revisions tested: 2, total time: 30m38.95979146s (build: 17m37.888816928s, test: 12m10.265928529s)
the crash still happens on HEAD
commit msg: Linux 4.14.212
crash: KASAN: use-after-free Read in __ext4_check_dir_entry
IPv6: ADDRCONF(NETDEV_CHANGE): macsec0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_vlan: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_vlan: link becomes ready
==================================================================
batman_adv: The newly added mac address (aa:aa:aa:aa:aa:3d) already exists on: batadv_slave_0
BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x2c6/0x3f0 fs/ext4/dir.c:82
Read of size 1 at addr ffff8881d8075001 by task syz-executor.2/7144

CPU: 1 PID: 7144 Comm: syz-executor.2 Not tainted 4.14.212-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/0x1f1 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.cold.7+0x11a/0x2d4 mm/kasan/report.c:409
batman_adv: It is strongly recommended to keep mac addresses unique to avoid problems!
 __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/0x2e00 fs/ext4/dir.c:240
batman_adv: The newly added mac address (aa:aa:aa:aa:aa:3d) already exists on: batadv_slave_0
 iterate_dir+0x188/0x660 fs/readdir.c:52
batman_adv: It is strongly recommended to keep mac addresses unique to avoid problems!
 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
IPv6: ADDRCONF(NETDEV_UP): batadv_slave_0: link is not ready
RIP: 0033:0x45cad9
RSP: 002b:00007f98388b3c78 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00000000004dd0a0 RCX: 000000000045cad9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000000f6 R14: 00000000004c3a80 R15: 00007f98388b46d4

The buggy address belongs to the page:
page:ffffea0007601d40 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x17ffe0000000000()
raw: 017ffe0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: ffff8881f672ee98 ffffea000763e9a0 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
batman_adv: batadv0: Interface activated: batadv_slave_0
 ffff8881d8074f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
IPv6: ADDRCONF(NETDEV_UP): veth1_macvtap: link is not ready
 ffff8881d8074f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881d8075000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8881d8075080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881d8075100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================