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

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Message-ID: <691d7c0f.a70a0220.2ea503.0014.GAE@google.com>
Date: Wed, 19 Nov 2025 00:13:03 -0800
From: syzbot <syzbot+ee60e584b5c6bb229126@...kaller.appspotmail.com>
To: albinbabuvarghese20@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [ext4?] KASAN: use-after-free Read in ext4_find_extent (4)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel panic: KASAN: panic_on_warn set ...

>ffff88806ecb8c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88806ecb8c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806ecb8d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Kernel panic - not syncing: KASAN: panic_on_warn set ...
CPU: 1 UID: 0 PID: 15465 Comm: syz.0.2193 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x99/0x250 lib/dump_stack.c:120
 vpanic+0x237/0x6d0 kernel/panic.c:489
 panic+0xb9/0xc0 kernel/panic.c:626
 check_panic_on_warn+0x89/0xb0 kernel/panic.c:376
 end_report+0x78/0x160 mm/kasan/report.c:227
 kasan_report+0x129/0x150 mm/kasan/report.c:597
 ext4_ext_rm_leaf fs/ext4/extents.c:2630 [inline]
 ext4_ext_remove_space+0x3211/0x42f0 fs/ext4/extents.c:2968
 ext4_ext_truncate+0x17e/0x300 fs/ext4/extents.c:4487
 ext4_truncate+0xb4f/0x12e0 fs/ext4/inode.c:4614
 ext4_truncate_failed_write fs/ext4/truncate.h:22 [inline]
 ext4_write_end+0x76e/0x9f0 fs/ext4/inode.c:1486
 ext4_da_write_end+0x84/0xcf0 fs/ext4/inode.c:3277
 generic_perform_write+0x62a/0x900 mm/filemap.c:4275
 ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5c9/0xb30 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd18e38e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd18f1a9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007fd18e5b5fa0 RCX: 00007fd18e38e929
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007fd18e410b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000e7c R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fd18e5b5fa0 R15: 00007ffe86830148
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..


Tested on:

commit:         8b690556 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1419e97c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6e611fe59206f39f
dashboard link: https://syzkaller.appspot.com/bug?extid=ee60e584b5c6bb229126
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1144b212580000