KASAN: use-after-free Read in ptdump_pte

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KASAN: use-after-free Read in ptdump_pte_entry mm	19				2	489d	504d	0/29	auto-obsoleted due to no activity on 2025/05/15 12:23
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BUG: KASAN: use-after-free in ptep_get include/linux/pgtable.h:461 [inline]
BUG: KASAN: use-after-free in ptdump_pte_entry+0xec/0x100 mm/ptdump.c:124
Read of size 8 at addr ffff88806640f530 by task syz.1.2229/17788

CPU: 0 UID: 0 PID: 17788 Comm: syz.1.2229 Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 ptep_get include/linux/pgtable.h:461 [inline]
 ptdump_pte_entry+0xec/0x100 mm/ptdump.c:124
 walk_pte_range_inner+0x258/0x370 mm/pagewalk.c:49
 walk_pte_range mm/pagewalk.c:80 [inline]
 walk_pmd_range mm/pagewalk.c:173 [inline]
 walk_pud_range mm/pagewalk.c:239 [inline]
 walk_p4d_range mm/pagewalk.c:280 [inline]
 walk_pgd_range+0xee1/0x1dd0 mm/pagewalk.c:321
 walk_kernel_page_table_range_lockless mm/pagewalk.c:664 [inline]
 walk_kernel_page_table_range mm/pagewalk.c:638 [inline]
 walk_page_range_debug+0x2fd/0x370 mm/pagewalk.c:696
 ptdump_walk_pgd+0x129/0x330 mm/ptdump.c:182
 ptdump_walk_pgd_level_core+0x26c/0x300 arch/x86/mm/dump_pagetables.c:458
 ptdump_show+0x1e/0x30 arch/x86/mm/debug_pagetables.c:10
 seq_read_iter+0x32f/0x1270 fs/seq_file.c:231
 seq_read+0x33b/0x4c0 fs/seq_file.c:163
 full_proxy_read+0x135/0x1a0 fs/debugfs/file.c:378
 vfs_read+0x1e4/0xb30 fs/read_write.c:572
 ksys_read+0x12a/0x250 fs/read_write.c:717
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9f8859ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9f89458028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f9f88815fa0 RCX: 00007f9f8859ce59
RDX: 000000000000001c RSI: 0000200000004c40 RDI: 0000000000000003
RBP: 00007f9f88632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9f88816038 R14: 00007f9f88815fa0 R15: 00007fff37ecdda8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x6640f
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00019900c8 ffffea00019902c8 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 0x40dc0(GFP_KERNEL|__GFP_ZERO|__GFP_COMP), pid 5628, tgid 5628 (syz-executor), ts 76048833593, free_ts 678067566484
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x11a6/0x3410 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5221
 alloc_pages_mpol+0x1fb/0x540 mm/mempolicy.c:2490
 alloc_pages_noprof+0x1a/0x160 mm/mempolicy.c:2581
 pagetable_alloc_noprof include/linux/mm.h:3651 [inline]
 __pte_alloc_one_kernel_noprof include/asm-generic/pgalloc.h:21 [inline]
 pte_alloc_one_kernel_noprof include/asm-generic/pgalloc.h:45 [inline]
 __pte_alloc_kernel+0x22/0x5c0 mm/memory.c:465
 vmap_pages_pte_range mm/vmalloc.c:537 [inline]
 vmap_pages_pmd_range mm/vmalloc.c:581 [inline]
 vmap_pages_pud_range mm/vmalloc.c:599 [inline]
 vmap_pages_p4d_range mm/vmalloc.c:617 [inline]
 vmap_small_pages_range_noflush+0x9d8/0xd50 mm/vmalloc.c:639
 __vmap_pages_range_noflush+0x601/0x660 mm/vmalloc.c:668
 vmap_pages_range_noflush mm/vmalloc.c:694 [inline]
 __vmap_pages_range mm/vmalloc.c:703 [inline]
 __vmalloc_area_node mm/vmalloc.c:3910 [inline]
 __vmalloc_node_range_noprof+0x9ed/0x1630 mm/vmalloc.c:4064
 vmalloc_user_noprof+0x9e/0xe0 mm/vmalloc.c:4218
 kcov_ioctl+0x4c/0x720 kernel/kcov.c:726
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 809 tgid 809 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1397 [inline]
 __free_frozen_pages+0x794/0x10a0 mm/page_alloc.c:2938
 __pagetable_free include/linux/mm.h:3661 [inline]
 kernel_pgtable_work_func+0x21a/0x2f0 mm/pgtable-generic.c:438
 process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
 process_scheduled_works kernel/workqueue.c:3397 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff88806640f400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806640f480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88806640f500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                     ^
 ffff88806640f580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806640f600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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