KASAN: use-after-free Read in ext4_xattr_set_entry (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    fb1c592cf4c9 Merge tag 'char-misc-4.19-rc7' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11431406400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
dashboard link: https://syzkaller.appspot.com/bug?extid=4a39a025912b265cacef
compiler:       gcc (GCC) 8.0.1 20180413 (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+4a39a025912b265cacef@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x2f6a/0x3d70  
fs/ext4/xattr.c:1600
Read of size 4 at addr ffff8801a4db491b by task syz-executor0/14364

CPU: 1 PID: 14364 Comm: syz-executor0 Not tainted 4.19.0-rc6+ #51
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+0x1c4/0x2b4 lib/dump_stack.c:113
 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_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 ext4_xattr_set_entry+0x2f6a/0x3d70 fs/ext4/xattr.c:1600
 ext4_xattr_ibody_set+0x8a/0x2c0 fs/ext4/xattr.c:2240
 ext4_xattr_set_handle+0xb8f/0x1650 fs/ext4/xattr.c:2394
 ext4_initxattrs+0xbd/0x120 fs/ext4/xattr_security.c:43
 security_inode_init_security+0x1d1/0x3d0 security/security.c:502
 ext4_init_security+0x34/0x40 fs/ext4/xattr_security.c:57
 __ext4_new_inode+0x4a6a/0x65b0 fs/ext4/ialloc.c:1160
 ext4_symlink+0x4b7/0x1130 fs/ext4/namei.c:3093
 vfs_symlink+0x37a/0x5d0 fs/namei.c:4127
 do_symlinkat+0x242/0x2d0 fs/namei.c:4154
 __do_sys_symlink fs/namei.c:4173 [inline]
 __se_sys_symlink fs/namei.c:4171 [inline]
 __x64_sys_symlink+0x59/0x80 fs/namei.c:4171
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4572a7
Code: 64 8b 5d 00 e9 14 fd ff ff 4c 8b 74 24 30 64 c7 45 00 22 00 00 00 bb  
22 00 00 00 e9 fd fc ff ff 0f 1f 00 b8 58 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 bd b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcaac01628 EFLAGS: 00000206 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004572a7
RDX: 00007ffcaac016a7 RSI: 00000000004bcfd0 RDI: 00007ffcaac01690
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000017
R10: 0000000000000075 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000b01 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0006936d00 count:0 mapcount:0 mapping:0000000000000000 index:0x1
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 dead000000000100 dead000000000200 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801a4db4800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801a4db4880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff8801a4db4900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8801a4db4980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801a4db4a00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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