linux-kernel - [syzbot] [ext4?] KASAN: use-after-free Read in ext4_find

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Message-ID: <6772fd43.050a0220.2f3838.04cd.GAE@google.com>
Date: Mon, 30 Dec 2024 12:06:27 -0800
From: syzbot <syzbot+ee60e584b5c6bb229126@...kaller.appspotmail.com>
To: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, tytso@....edu
Subject: [syzbot] [ext4?] KASAN: use-after-free Read in ext4_find_extent (4)

Hello,

syzbot found the following issue on:

HEAD commit:    573067a5a685 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=136d1018580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cd7202b56d469648
dashboard link: https://syzkaller.appspot.com/bug?extid=ee60e584b5c6bb229126
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1790a0b0580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee82c4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9d3b5c855aa0/disk-573067a5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0c06fc1ead83/vmlinux-573067a5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3390e59b9e4b/Image-573067a5.gz.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/ef6b4e51a02a/mount_0.gz
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/1e15bbc4371d/mount_1.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ee60e584b5c6bb229126@...kaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0x94c/0xb0c fs/ext4/extents.c:955
Read of size 4 at addr ffff0000e2d145a0 by task kworker/u8:4/45

CPU: 1 UID: 0 PID: 45 Comm: kworker/u8:4 Not tainted 6.13.0-rc3-syzkaller-g573067a5a685 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: writeback wb_workfn (flush-7:0)
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xe4/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x198/0x538 mm/kasan/report.c:489
 kasan_report+0xd8/0x138 mm/kasan/report.c:602
 __asan_report_load4_noabort+0x20/0x2c mm/kasan/report_generic.c:380
 ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
 ext4_find_extent+0x94c/0xb0c fs/ext4/extents.c:955
 ext4_ext_map_blocks+0x2b0/0x6600 fs/ext4/extents.c:4205
 ext4_map_create_blocks fs/ext4/inode.c:516 [inline]
 ext4_map_blocks+0x710/0x15d0 fs/ext4/inode.c:702
 mpage_map_one_extent fs/ext4/inode.c:2219 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2272 [inline]
 ext4_do_writepages+0x195c/0x318c fs/ext4/inode.c:2735
 ext4_writepages+0x198/0x308 fs/ext4/inode.c:2824
 do_writepages+0x304/0x7d0 mm/page-writeback.c:2702
 __writeback_single_inode+0x15c/0x15a4 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x650/0x1088 fs/fs-writeback.c:1976
 wb_writeback+0x3e0/0xe9c fs/fs-writeback.c:2156
 wb_do_writeback fs/fs-writeback.c:2303 [inline]
 wb_workfn+0x38c/0x1048 fs/fs-writeback.c:2343
 process_one_work+0x7a8/0x15cc kernel/workqueue.c:3229
 process_scheduled_works kernel/workqueue.c:3310 [inline]
 worker_thread+0x97c/0xeec kernel/workqueue.c:3391
 kthread+0x288/0x310 kernel/kthread.c:389
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:862

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff9b78a pfn:0x122d14
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000ffff9b78a 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000e2d14480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000e2d14500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff0000e2d14580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff0000e2d14600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000e2d14680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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