KASAN: use-after-free Read in ext4_read_inline_data (2)

Status: upstream: reported C repro on 2026/09/14 16:38
Subsystems: ext4
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+085a394c92518a04fd09@syzkaller.appspotmail.com
First crash: 17h22m, last: 17h22m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
4353d80d assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: use-after-free Read in ext4_read_inline_data (2) 2026/09/14 00:19 2026/09/14 00:19 2026/09/14 01:15 70a60e12
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Title Replies (including bot) Last reply
[syzbot] [ext4?] KASAN: use-after-free Read in ext4_read_inline_data (2) 0 (1) 2026/09/14 16:38
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: use-after-free Read in ext4_read_inline_data ext4 19 syz, C 4 248d 244d 0/29 auto-obsoleted due to no activity on 2026/04/19 11:05
linux-6.6 KASAN: slab-use-after-free Read in ext4_read_inline_data origin:upstream 19 syz, C 4 20d 85d 0/2 upstream: reported C repro on 2026/06/21 05:23

Sample crash report:
=========
==================================================================
BUG: KASAN: use-after-free in ext4_read_inline_data+0x1c9/0x2b0 fs/ext4/inline.c:213
Read of size 68 at addr ffff8880723bf51a by task syz-executor313/5649

CPU: 1 UID: 0 PID: 5649 Comm: syz-executor313 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 ext4_read_inline_data+0x1c9/0x2b0 fs/ext4/inline.c:213
 ext4_read_inline_dir+0x320/0xc20 fs/ext4/inline.c:1422
 ext4_readdir+0x46c/0x4250 fs/ext4/dir.c:164
 iterate_dir+0x2e2/0x4d0 fs/readdir.c:110
 __do_sys_getdents64 fs/readdir.c:399 [inline]
 __se_sys_getdents64+0xf1/0x280 fs/readdir.c:384
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f74cc073df3
Code: 48 0f 45 c2 48 83 c4 08 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 ff ff ff 7f 48 39 c2 48 0f 47 d0 b8 d9 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 c7 c2 d0 ff ff ff f7 d8
RSP: 002b:00007fff22d6b888 EFLAGS: 00000293 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 0000555562e4b9d0 RCX: 00007f74cc073df3
RDX: 0000000000008000 RSI: 0000555562e4ba00 RDI: 0000000000000005
RBP: 0000555562e4ba00 R08: 00007f74cc0e35a0 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000293 R12: 0000555562e4b9d4
R13: ffffffffffffffd0 R14: 0000000000000016 R15: 431bde82d7b634db
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x723bf
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001c86008 ffffea0001c8ef88 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x500cc2(GFP_HIGHUSER|__GFP_ACCOUNT), pid 5495, tgid 5495 (sshd-session), ts 69474537754
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2209/0x2280 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x217/0x5a0 mm/page_alloc.c:5436
 alloc_pages_mpol+0x21e/0x390 mm/mempolicy.c:2486
 alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
 alloc_pages_noprof+0xb1/0x2b0 mm/mempolicy.c:2577
 anon_pipe_prefill_and_lock fs/pipe.c:158 [inline]
 anon_pipe_write+0x21b/0x1a30 fs/pipe.c:534
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5499 tgid 5499 ts 69475806887 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_frozen_pages+0xc93/0xd90 mm/page_alloc.c:2962
 __folio_put+0x4b3/0x590 mm/folio.c:105
 folio_put include/linux/mm.h:2160 [inline]
 put_page include/linux/mm.h:2229 [inline]
 anon_pipe_trim_and_unlock+0x3e2/0x520 fs/pipe.c:191
 anon_pipe_read+0xf1c/0x10c0 fs/pipe.c:472
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x595/0xa80 fs/read_write.c:574
 ksys_read+0x150/0x270 fs/read_write.c:716
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880723bf400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880723bf480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880723bf500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8880723bf580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880723bf600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/14 00:17 upstream 2f0c1cf72f46 70a60e12 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-kasan-gce-root KASAN: use-after-free Read in ext4_read_inline_data
* Struck through repros no longer work on HEAD.