linux-kernel - Re: [syzbot] [ext4?] KASAN: slab-out-of-bounds Read in ext4_search

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Message-ID: <68df8ab8.050a0220.2c17c1.001c.GAE@google.com>
Date: Fri, 03 Oct 2025 01:35:04 -0700
From: syzbot <syzbot+3ee481e21fd75e14c397@...kaller.appspotmail.com>
To: kartikey406@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [ext4?] KASAN: slab-out-of-bounds Read in ext4_search_dir

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in ext4_search_dir

loop0: detected capacity change from 1024 to 767
==================================================================
BUG: KASAN: use-after-free in ext4_search_dir+0xf1/0x1b0 fs/ext4/namei.c:1469
Read of size 1 at addr ffff888047c19e53 by task syz.0.25/5994

CPU: 0 UID: 0 PID: 5994 Comm: syz.0.25 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 ext4_search_dir+0xf1/0x1b0 fs/ext4/namei.c:1469
 ext4_find_inline_entry+0x492/0x5f0 fs/ext4/inline.c:1621
 __ext4_find_entry+0x2fd/0x1f20 fs/ext4/namei.c:1542
 ext4_lookup_entry fs/ext4/namei.c:1703 [inline]
 ext4_lookup+0x13d/0x6c0 fs/ext4/namei.c:1771
 lookup_open fs/namei.c:3774 [inline]
 open_last_lookups fs/namei.c:3895 [inline]
 path_openat+0x10fe/0x3830 fs/namei.c:4131
 do_filp_open+0x1fa/0x410 fs/namei.c:4161
 do_sys_openat2+0x121/0x1c0 fs/open.c:1435
 do_sys_open fs/open.c:1450 [inline]
 __do_sys_creat fs/open.c:1528 [inline]
 __se_sys_creat fs/open.c:1522 [inline]
 __x64_sys_creat+0x8f/0xc0 fs/open.c:1522
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f30dc98eec9
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:00007f30dd80c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007f30dcbe5fa0 RCX: 00007f30dc98eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000100
RBP: 00007f30dca11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f30dcbe6038 R14: 00007f30dcbe5fa0 R15: 00007ffd1c506f18
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x1ce pfn:0x47c19
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea00011f0688 ffffea00011f6088 0000000000000000
raw: 00000000000001ce 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 5999, tgid 5999 (cmp), ts 160342984478, free_ts 160390502500
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
 prep_new_page mm/page_alloc.c:1858 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 folio_alloc_mpol_noprof mm/mempolicy.c:2435 [inline]
 vma_alloc_folio_noprof+0xe4/0x200 mm/mempolicy.c:2470
 folio_prealloc+0x30/0x180 mm/memory.c:-1
 wp_page_copy mm/memory.c:3679 [inline]
 do_wp_page+0x1231/0x5800 mm/memory.c:4140
 handle_pte_fault mm/memory.c:6193 [inline]
 __handle_mm_fault+0x1033/0x5400 mm/memory.c:6318
 handle_mm_fault+0x40a/0x8e0 mm/memory.c:6487
 do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
page last free pid 5999 tgid 5999 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:2963
 folios_put_refs+0x584/0x670 mm/swap.c:1002
 free_pages_and_swap_cache+0x277/0x520 mm/swap_state.c:355
 __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
 tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:397 [inline]
 tlb_flush_mmu+0x3a0/0x680 mm/mmu_gather.c:404
 tlb_finish_mmu+0xc3/0x1d0 mm/mmu_gather.c:497
 exit_mmap+0x444/0xb40 mm/mmap.c:1293
 __mmput+0x118/0x430 kernel/fork.c:1133
 exit_mm+0x1da/0x2c0 kernel/exit.c:582
 do_exit+0x648/0x2300 kernel/exit.c:954
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
 __do_sys_exit_group kernel/exit.c:1118 [inline]
 __se_sys_exit_group kernel/exit.c:1116 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1116
 x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888047c19d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888047c19d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888047c19e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                 ^
 ffff888047c19e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888047c19f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         e406d57b Merge tag 'mm-nonmm-stable-2025-10-02-15-29' ..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126965cd980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=84e81c4d0c0e900a
dashboard link: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
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=13911ee2580000