KASAN: use-after-free Read in ext4_xattr_set_entry (3)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c2003765 Merge tag 'io_uring-5.6-2020-03-07' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1671b01de00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4527d1e2fb19fd5c
dashboard link: https://syzkaller.appspot.com/bug?extid=15fbdaa8666ea08754f4
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+15fbdaa8666ea08754f4@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in memmove include/linux/string.h:396 [inline]
BUG: KASAN: use-after-free in ext4_xattr_set_entry+0xafc/0x34f0 fs/ext4/xattr.c:1714
Read of size 4 at addr ffff888035a85ffe by task syz-executor.3/12471

CPU: 1 PID: 12471 Comm: syz-executor.3 Not tainted 5.6.0-rc4-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+0x188/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:374
 __kasan_report.cold+0x1a/0x32 mm/kasan/report.c:506
 kasan_report+0xe/0x20 mm/kasan/common.c:641
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x128/0x190 mm/kasan/generic.c:192
 memmove+0x20/0x50 mm/kasan/common.c:117
 memmove include/linux/string.h:396 [inline]
 ext4_xattr_set_entry+0xafc/0x34f0 fs/ext4/xattr.c:1714
 ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2216
 ext4_xattr_set_handle+0x933/0x1200 fs/ext4/xattr.c:2372
 ext4_xattr_set+0x1fc/0x390 fs/ext4/xattr.c:2484
 __vfs_setxattr+0x10e/0x170 fs/xattr.c:150
 __vfs_setxattr_noperm+0x11a/0x410 fs/xattr.c:181
 vfs_setxattr+0xd2/0xf0 fs/xattr.c:224
 setxattr+0x23d/0x330 fs/xattr.c:451
 path_setxattr+0x170/0x190 fs/xattr.c:470
 __do_sys_setxattr fs/xattr.c:485 [inline]
 __se_sys_setxattr fs/xattr.c:481 [inline]
 __x64_sys_setxattr+0xc0/0x160 fs/xattr.c:481
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c4a9
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ff39057ac78 EFLAGS: 00000246 ORIG_RAX: 00000000000000bc
RAX: ffffffffffffffda RBX: 00007ff39057b6d4 RCX: 000000000045c4a9
RDX: 00000000200000c0 RSI: 0000000020000040 RDI: 0000000020000000
RBP: 000000000076bf20 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000016 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000b49 R14: 00000000004d77d8 R15: 000000000076bf2c

The buggy address belongs to the page:
page:ffffea0000d6a140 refcount:2 mapcount:0 mapping:ffff8880a2f5dba0 index:0x43a
def_blk_aops
flags: 0xfffe000000203a(referenced|dirty|lru|active|private)
raw: 00fffe000000203a ffffea00010ca048 ffffea00010d3ac8 ffff8880a2f5dba0
raw: 000000000000043a ffff888086c77930 00000002ffffffff ffff88804831c000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88804831c000

Memory state around the buggy address:
 ffff888035a85f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888035a85f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888035a86000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff888035a86080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888035a86100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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