[syzbot] [net?] KASAN: use-after-free Read in filemap_map_pages

[syzbot] [net?] KASAN: use-after-free Read in filemap_map_pages

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    d60ec36cab33 Merge tag 'mm-hotfixes-stable-2026-05-25-16-2..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=124501ec580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8d24a1331e060dda
dashboard link: https://syzkaller.appspot.com/bug?extid=b72767277f29b6407083
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/864236422e21/disk-d60ec36c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/858219f0a900/vmlinux-d60ec36c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/809d091c238e/bzImage-d60ec36c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b72767277f29b6407083@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in ptep_get include/linux/pgtable.h:461 [inline]
BUG: KASAN: use-after-free in filemap_map_order0_folio mm/filemap.c:3856 [inline]
BUG: KASAN: use-after-free in filemap_map_pages+0xc7a/0x2100 mm/filemap.c:3932
Read of size 8 at addr ffff88807bed6d50 by task syz.1.7707/30545

CPU: 1 UID: 0 PID: 30545 Comm: syz.1.7707 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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
 ptep_get include/linux/pgtable.h:461 [inline]
 filemap_map_order0_folio mm/filemap.c:3856 [inline]
 filemap_map_pages+0xc7a/0x2100 mm/filemap.c:3932
 do_fault_around mm/memory.c:5867 [inline]
 do_read_fault mm/memory.c:5900 [inline]
 do_fault mm/memory.c:6043 [inline]
 do_pte_missing+0x1f38/0x33f0 mm/memory.c:4566
 handle_pte_fault mm/memory.c:6427 [inline]
 __handle_mm_fault mm/memory.c:6565 [inline]
 handle_mm_fault+0x1bf2/0x3170 mm/memory.c:6734
 do_user_addr_fault+0x75b/0x1340 arch/x86/mm/fault.c:1385
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0010:rep_movs_alternative+0x30/0x90 arch/x86/lib/copy_user_64.S:60
Code: 83 f9 08 73 25 85 c9 74 0f 8a 06 88 07 48 ff c7 48 ff c6 48 ff c9 75 f1 c3 cc cc cc cc 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 <48> 8b 06 48 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 db 83 f9 08
RSP: 0000:ffffc9000cb978b8 EFLAGS: 00050206
RAX: 00007ffffffff001 RBX: 000000000000001c RCX: 000000000000001c
RDX: 0000000000000001 RSI: 00000000800bcae0 RDI: ffffc9000cb97940
RBP: ffffc9000cb979d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52001972f2b R12: dffffc0000000000
R13: ffffc9000cb97c80 R14: ffffc9000cb97940 R15: 00000000800bcae0
 copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:141 [inline]
 _inline_copy_from_user include/linux/uaccess.h:185 [inline]
 _copy_from_user+0x7a/0xb0 lib/usercopy.c:18
 copy_from_user include/linux/uaccess.h:223 [inline]
 get_compat_msghdr+0xb3/0x4c0 net/compat.c:91
 recvmsg_copy_msghdr net/socket.c:2882 [inline]
 ___sys_recvmsg+0x1dd/0x590 net/socket.c:2956
 do_recvmmsg+0x3a5/0x800 net/socket.c:3047
 __sys_recvmmsg+0x1a5/0x290 net/socket.c:3129
 __do_compat_sys_recvmmsg_time32 net/compat.c:418 [inline]
 __se_compat_sys_recvmmsg_time32 net/compat.c:414 [inline]
 __ia32_compat_sys_recvmmsg_time32+0xbf/0xe0 net/compat.c:414
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x229/0x6e0 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x33/0x70 arch/x86/entry/syscall_32.c:332
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7fa501c
Code: 90 85 d2 74 0a 89 ce 81 e6 ff 0f 00 00 89 32 85 c0 74 05 c1 e9 0c 89 08 31 c0 5e 5d c3 90 0f 1f 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 58 b8
RSP: 002b:00000000f544550c EFLAGS: 00000206 ORIG_RAX: 0000000000000151
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00000000800000c0
RDX: 0000000000010106 RSI: 0000000000000002 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x121f pfn:0x7bed6
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f0(buddy)
raw: 00fff00000000000 ffffea0000fea188 ffffea0002346808 0000000000000000
raw: 000000000000121f 0000000000000000 00000000f0000000 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 0x140cc2(GFP_HIGHUSER|__GFP_COMP), pid 29415, tgid 29414 (syz.1.7355), ts 1634224509357, free_ts 1634614223058
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x22d/0x280 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x2593/0x2610 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5221
 alloc_pages_mpol+0x235/0x490 mm/mempolicy.c:2490
 alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
 alloc_pages_noprof+0xac/0x2a0 mm/mempolicy.c:2581
 folio_alloc_noprof+0x1e/0x30 mm/mempolicy.c:2591
 filemap_alloc_folio_noprof+0x111/0x470 mm/filemap.c:1014
 filemap_create_folio mm/filemap.c:2612 [inline]
 filemap_get_pages+0x819/0x1ef0 mm/filemap.c:2702
 filemap_read+0x447/0x1230 mm/filemap.c:2806
 __kernel_read+0x504/0x9b0 fs/read_write.c:532
 integrity_kernel_read+0x89/0xd0 security/integrity/iint.c:28
 ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:222 [inline]
 ima_calc_file_hash+0x446/0x860 security/integrity/ima/ima_crypto.c:280
 ima_collect_measurement+0x51d/0x9c0 security/integrity/ima/ima_api.c:300
 process_measurement+0x12cd/0x1c80 security/integrity/ima/ima_main.c:425
 ima_file_check+0xe1/0x130 security/integrity/ima/ima_main.c:685
 security_file_post_open+0xb3/0x260 security/security.c:2755
page last free pid 29415 tgid 29414 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1397 [inline]
 free_unref_folios+0xd9f/0x14c0 mm/page_alloc.c:2999
 folios_put_refs+0x9ff/0xb40 mm/swap.c:1008
 folio_batch_release include/linux/folio_batch.h:101 [inline]
 truncate_inode_pages_range+0x3dd/0xe30 mm/truncate.c:408
 evict+0x631/0xb10 fs/inode.c:843
 __dentry_kill+0x1a2/0x690 fs/dcache.c:718
 shrink_kill+0xa9/0x2c0 fs/dcache.c:1195
 shrink_dentry_list+0x2e0/0x5e0 fs/dcache.c:1222
 shrink_dcache_tree+0xe9/0x5d0 fs/dcache.c:-1
 do_one_tree fs/dcache.c:1721 [inline]
 shrink_dcache_for_umount+0xa8/0x1f0 fs/dcache.c:1738
 generic_shutdown_super+0x6f/0x2d0 fs/super.c:624
 kill_anon_super+0x3b/0x70 fs/super.c:1292
 deactivate_locked_super+0xbc/0x130 fs/super.c:476
 cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x70f/0x22c0 kernel/exit.c:976
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1119

Memory state around the buggy address:
 ffff88807bed6c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88807bed6c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88807bed6d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                 ^
 ffff88807bed6d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88807bed6e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
----------------
Code disassembly (best guess):
   0:	83 f9 08             	cmp    $0x8,%ecx
   3:	73 25                	jae    0x2a
   5:	85 c9                	test   %ecx,%ecx
   7:	74 0f                	je     0x18
   9:	8a 06                	mov    (%rsi),%al
   b:	88 07                	mov    %al,(%rdi)
   d:	48 ff c7             	inc    %rdi
  10:	48 ff c6             	inc    %rsi
  13:	48 ff c9             	dec    %rcx
  16:	75 f1                	jne    0x9
  18:	c3                   	ret
  19:	cc                   	int3
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	cc                   	int3
  1d:	66 2e 0f 1f 84 00 00 	cs nopw 0x0(%rax,%rax,1)
  24:	00 00 00
  27:	0f 1f 00             	nopl   (%rax)
* 2a:	48 8b 06             	mov    (%rsi),%rax <-- trapping instruction
  2d:	48 89 07             	mov    %rax,(%rdi)
  30:	48 83 c6 08          	add    $0x8,%rsi
  34:	48 83 c7 08          	add    $0x8,%rdi
  38:	83 e9 08             	sub    $0x8,%ecx
  3b:	74 db                	je     0x18
  3d:	83 f9 08             	cmp    $0x8,%ecx


---
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