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KASAN: use-after-free Read in ext4_read_inline_data

Status: upstream: reported C repro on 2026/01/13 01:31
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+6986a30df88382d1f7bf@syzkaller.appspotmail.com
First crash: 4d01h, last: 3d22h
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [ext4?] KASAN: use-after-free Read in ext4_read_inline_data 0 (2) 2026/01/13 06:43
Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/01/13 06:43 20m kartikey406@gmail.com patch upstream OK log

Sample crash report:
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
loop0: detected capacity change from 2048 to 2045
==================================================================
BUG: KASAN: use-after-free in ext4_read_inline_data+0x1d0/0x2c0 fs/ext4/inline.c:214
Read of size 68 at addr ffff8880566c2810 by task syz.0.17/5510

CPU: 0 UID: 0 PID: 5510 Comm: syz.0.17 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+0xe8/0x150 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
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:200
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 ext4_read_inline_data+0x1d0/0x2c0 fs/ext4/inline.c:214
 ext4_read_inline_dir+0x2b3/0xb80 fs/ext4/inline.c:1405
 ext4_readdir+0x3e8/0x3e90 fs/ext4/dir.c:162
 iterate_dir+0x399/0x570 fs/readdir.c:108
 __do_sys_getdents64 fs/readdir.c:410 [inline]
 __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f97a4b8f7c9
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:00007f97a59cc038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f97a4de5fa0 RCX: 00007f97a4b8f7c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007f97a4c13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f97a4de6038 R14: 00007f97a4de5fa0 R15: 00007fff8c641cb8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x7fd834db2 pfn:0x566c2
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea000159b0c8 ffffea000159b148 0000000000000000
raw: 00000007fd834db2 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 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO|__GFP_COMP), pid 5511, tgid 5511 (rm), ts 103393754947, free_ts 103419734757
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1857
 prep_new_page mm/page_alloc.c:1865 [inline]
 get_page_from_freelist+0x24e0/0x2580 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof mm/mempolicy.c:2505 [inline]
 vma_alloc_folio_noprof+0xe4/0x200 mm/mempolicy.c:2540
 folio_prealloc+0x30/0x180 mm/memory.c:-1
 alloc_anon_folio mm/memory.c:5165 [inline]
 do_anonymous_page mm/memory.c:5222 [inline]
 do_pte_missing+0x14e8/0x3330 mm/memory.c:4399
 handle_pte_fault mm/memory.c:6273 [inline]
 __handle_mm_fault mm/memory.c:6411 [inline]
 handle_mm_fault+0x1b26/0x32b0 mm/memory.c:6580
 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+0x71/0xd0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
page last free pid 5511 tgid 5511 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1406 [inline]
 free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:3000
 folios_put_refs+0x584/0x670 mm/swap.c:1002
 free_pages_and_swap_cache+0x4be/0x520 mm/swap_state.c:358
 __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+0x439/0xb10 mm/mmap.c:1290
 __mmput+0x118/0x430 kernel/fork.c:1173
 exit_mm+0x169/0x230 kernel/exit.c:581
 do_exit+0x627/0x22f0 kernel/exit.c:959
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 __do_sys_exit_group kernel/exit.c:1123 [inline]
 __se_sys_exit_group kernel/exit.c:1121 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1121
 __pfx_syscall_get_nr+0x0/0x10 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880566c2700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880566c2780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880566c2800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                         ^
 ffff8880566c2880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880566c2900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/09 11:05 upstream 54e82e93ca93 d1b870e1 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-snapshot-upstream-root KASAN: use-after-free Read in ext4_read_inline_data
2026/01/09 09:27 upstream 54e82e93ca93 d1b870e1 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-snapshot-upstream-root KASAN: use-after-free Read in ext4_read_inline_data
2026/01/09 10:16 upstream 54e82e93ca93 d1b870e1 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in ext4_read_inline_data
2026/01/09 08:42 upstream 54e82e93ca93 d1b870e1 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: use-after-free Read in ext4_read_inline_data
* Struck through repros no longer work on HEAD.