syzbot
KASAN: use-after-free Read in filemap_map_pages
Status:
upstream: reported C repro on 2026/06/01 11:47
Labels:
prio:high
actionable
[Documentation on labels]
Reported-by: syzbot+b72767277f29b6407083@syzkaller.appspotmail.com
First crash: 103d, last: 9d00h
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✨ AI Patch Versions (5)
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Last patch testing requests (4)
Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ptep_get include/linux/pgtable.h:495 [inline]
BUG: KASAN: use-after-free in filemap_map_folio_range mm/filemap.c:3820 [inline]
BUG: KASAN: use-after-free in filemap_map_pages+0x1b75/0x1f80 mm/filemap.c:3955
Read of size 8 at addr ffff88803f851a00 by task syz-executor403/6035
CPU: 2 UID: 0 PID: 6035 Comm: syz-executor403 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
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/0x1c0 mm/kasan/report.c:595
ptep_get include/linux/pgtable.h:495 [inline]
filemap_map_folio_range mm/filemap.c:3820 [inline]
filemap_map_pages+0x1b75/0x1f80 mm/filemap.c:3955
do_fault_around mm/memory.c:5818 [inline]
do_read_fault mm/memory.c:5851 [inline]
do_fault+0x985/0x1750 mm/memory.c:5994
do_pte_missing mm/memory.c:4566 [inline]
handle_pte_fault mm/memory.c:6379 [inline]
__handle_mm_fault+0x187d/0x2a00 mm/memory.c:6517
handle_mm_fault+0x37b/0xa30 mm/memory.c:6686
do_user_addr_fault+0x74c/0x12f0 arch/x86/mm/fault.c:1394
handle_page_fault arch/x86/mm/fault.c:1483 [inline]
exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1536
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
RIP: 0010:fault_in_readable+0xde/0x190 mm/gup.c:2161
Code: 68 46 ae ff 4c 89 f0 48 85 c0 0f 85 bf 00 00 00 e8 77 4c ae ff 0f 01 cb 0f ae e8 4c 89 fb 4d 85 ff 75 31 eb 48 e8 62 4c ae ff <44> 8a 33 e8 5a 4c ae ff 48 81 c3 00 10 00 00 31 ff 48 81 e3 00 f0
RSP: 0018:ffffc90003a87af8 EFLAGS: 00050293
RAX: 0000000000000000 RBX: 00007fe62c200000 RCX: ffffffff825c2758
RDX: ffff888033b84a80 RSI: ffffffff825c271e RDI: ffff888033b84a80
RBP: 00007fe62c200001 R08: 0000000000000006 R09: 00007fe62c200001
R10: 00007fe62c200000 R11: 0000000000000000 R12: 0000000000000001
R13: 1ffff92000750f60 R14: 0000000000000000 R15: 00007fe62c200000
fault_in_iov_iter_readable+0x101/0x2c0 lib/iov_iter.c:106
generic_perform_write+0x863/0xa40 mm/filemap.c:4413
shmem_file_write_iter+0x10e/0x140 mm/shmem.c:3424
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_pwrite64 fs/read_write.c:794 [inline]
__do_sys_pwrite64 fs/read_write.c:802 [inline]
__se_sys_pwrite64 fs/read_write.c:799 [inline]
__x64_sys_pwrite64+0x1eb/0x250 fs/read_write.c:799
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe62c7fce5e
Code: 08 0f 85 f5 e2 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007fe62b9fe1a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007fe62b9fe6c0 RCX: 00007fe62c7fce5e
RDX: 0000000000000001 RSI: 00007fe62c200000 RDI: 0000000000000003
RBP: 0000000000000021 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffdde346d90 R15: 00007ffdde346e78
</TASK>
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888000000000 pfn:0x3f851
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: ffff888000000000 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 0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_COMP), pid 6004, tgid 6004 (cmp), ts 79653237963, free_ts 79740307238
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304
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:3685 [inline]
pmd_alloc_one_noprof include/asm-generic/pgalloc.h:143 [inline]
__pmd_alloc+0x3b/0x950 mm/memory.c:6772
pmd_alloc include/linux/mm.h:3601 [inline]
__handle_mm_fault+0xa9c/0x2a00 mm/memory.c:6469
handle_mm_fault+0x37b/0xa30 mm/memory.c:6686
do_user_addr_fault+0x5a3/0x12f0 arch/x86/mm/fault.c:1343
handle_page_fault arch/x86/mm/fault.c:1483 [inline]
exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1536
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
page last free pid 6002 tgid 6002 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0x79f/0x1090 mm/page_alloc.c:2950
__pagetable_free include/linux/mm.h:3695 [inline]
pagetable_free include/linux/mm.h:3719 [inline]
pagetable_dtor_free include/linux/mm.h:3818 [inline]
__tlb_remove_table include/asm-generic/tlb.h:221 [inline]
__tlb_remove_table_free mm/mmu_gather.c:228 [inline]
tlb_remove_table_rcu+0x2cf/0x380 mm/mmu_gather.c:291
rcu_do_batch kernel/rcu/tree.c:2645 [inline]
rcu_core+0x5a2/0x10d0 kernel/rcu/tree.c:2897
handle_softirqs+0x1ea/0x9b0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x162/0x210 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
Memory state around the buggy address:
ffff88803f851900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88803f851980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88803f851a00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88803f851a80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88803f851b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
----------------
Code disassembly (best guess):
0: 68 46 ae ff 4c push $0x4cffae46
5: 89 f0 mov %esi,%eax
7: 48 85 c0 test %rax,%rax
a: 0f 85 bf 00 00 00 jne 0xcf
10: e8 77 4c ae ff call 0xffae4c8c
15: 0f 01 cb stac
18: 0f ae e8 lfence
1b: 4c 89 fb mov %r15,%rbx
1e: 4d 85 ff test %r15,%r15
21: 75 31 jne 0x54
23: eb 48 jmp 0x6d
25: e8 62 4c ae ff call 0xffae4c8c
* 2a: 44 8a 33 mov (%rbx),%r14b <-- trapping instruction
2d: e8 5a 4c ae ff call 0xffae4c8c
32: 48 81 c3 00 10 00 00 add $0x1000,%rbx
39: 31 ff xor %edi,%edi
3b: 48 rex.W
3c: 81 .byte 0x81
3d: e3 00 jrcxz 0x3f
3f: f0 lock
Struck through repros no longer work on HEAD.