[syzbot ci] Re: Implement a new generic pagewalk API

syzbot ci
2026-04-13T07:38:42Z

syzbot ci has tested the following series

[v1] Implement a new generic pagewalk API
https://lore.kernel.org/all/20260412174244.133715-1-osalvador@suse.de
* [RFC PATCH 1/7] mm: Add softleaf_from_pud
* [RFC PATCH 2/7] mm: Add {pmd,pud}_huge_lock helper
* [RFC PATCH 3/7] mm: Implement folio_pmd_batch
* [RFC PATCH 4/7] mm: Implement pt_range_walk
* [RFC PATCH 5/7] mm: Make /proc/pid/smaps use the new generic pagewalk API
* [RFC PATCH 6/7] mm: Make /proc/pid/numa_maps use the new generic pagewalk API
* [RFC PATCH 7/7] mm: Make /proc/pid/pagemap use the new generic pagewalk API

and found the following issues:
* KASAN: slab-out-of-bounds Write in pagemap_read
* WARNING in pt_range_walk

Full report is available here:
https://ci.syzbot.org/series/1f85248a-1ac0-48e8-8ce3-edb89a6b9ee5

***

KASAN: slab-out-of-bounds Write in pagemap_read

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 857fa8f2a5b184c206c703a3d9ce05cea683cfed
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/932ed80d-9fb1-4c99-8096-4b7a9324bb7c/config
syz repro: https://ci.syzbot.org/findings/1083a63d-0470-4ce7-8943-0a60046b9269/syz_repro

==================================================================
BUG: KASAN: slab-out-of-bounds in add_to_pagemap fs/proc/task_mmu.c:1740 [inline]
BUG: KASAN: slab-out-of-bounds in pagemap_read_walk_range fs/proc/task_mmu.c:2736 [inline]
BUG: KASAN: slab-out-of-bounds in pagemap_read+0x19bc/0x21a0 fs/proc/task_mmu.c:2829
Write of size 8 at addr ffff88816d32b000 by task syz.0.17/5958

CPU: 0 UID: 0 PID: 5958 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 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+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
add_to_pagemap fs/proc/task_mmu.c:1740 [inline]
pagemap_read_walk_range fs/proc/task_mmu.c:2736 [inline]
pagemap_read+0x19bc/0x21a0 fs/proc/task_mmu.c:2829
vfs_read+0x20c/0xa70 fs/read_write.c:572
ksys_pread64 fs/read_write.c:765 [inline]
__do_sys_pread64 fs/read_write.c:773 [inline]
__se_sys_pread64 fs/read_write.c:770 [inline]
__x64_sys_pread64+0x199/0x230 fs/read_write.c:770
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd47239c819
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:00007fd473284028 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007fd472615fa0 RCX: 00007fd47239c819
RDX: 0000000000019000 RSI: 0000200000000200 RDI: 0000000000000003
RBP: 00007fd472432c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000001000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd472616038 R14: 00007fd472615fa0 R15: 00007ffe3c81aa88
</TASK>

Allocated by task 5958:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5339
kmalloc_noprof include/linux/slab.h:962 [inline]
kmalloc_array_noprof include/linux/slab.h:1109 [inline]
pagemap_read+0x287/0x21a0 fs/proc/task_mmu.c:2781
vfs_read+0x20c/0xa70 fs/read_write.c:572
ksys_pread64 fs/read_write.c:765 [inline]
__do_sys_pread64 fs/read_write.c:773 [inline]
__se_sys_pread64 fs/read_write.c:770 [inline]
__x64_sys_pread64+0x199/0x230 fs/read_write.c:770
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88816d32a000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 0 bytes to the right of
allocated 4096-byte region [ffff88816d32a000, ffff88816d32b000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x16d328
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x57ff00000000040(head|node=1|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 057ff00000000040 ffff888100042140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 057ff00000000040 ffff888100042140 dead000000000100 dead000000000122
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 057ff00000000003 ffffea0005b4ca01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 20801987900, free_ts 13278585415
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
prep_new_page mm/page_alloc.c:1897 [inline]
get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
alloc_slab_page mm/slub.c:3255 [inline]
allocate_slab+0x77/0x660 mm/slub.c:3444
new_slab mm/slub.c:3502 [inline]
refill_objects+0x331/0x3c0 mm/slub.c:7134
refill_sheaf mm/slub.c:2804 [inline]
__pcs_replace_empty_main+0x2b9/0x620 mm/slub.c:4578
alloc_from_pcs mm/slub.c:4681 [inline]
slab_alloc_node mm/slub.c:4815 [inline]
__kmalloc_cache_noprof+0x392/0x660 mm/slub.c:5334
kmalloc_noprof include/linux/slab.h:962 [inline]
kzalloc_noprof include/linux/slab.h:1200 [inline]
kobject_uevent_env+0x28c/0x9e0 lib/kobject_uevent.c:540
driver_register+0x2d4/0x320 drivers/base/driver.c:257
usb_register_driver+0x1e4/0x390 drivers/usb/core/driver.c:1078
hid_init+0x39/0x70 drivers/hid/usbhid/hid-core.c:1710
do_one_initcall+0x250/0x8d0 init/main.c:1382
do_initcall_level+0x104/0x190 init/main.c:1444
do_initcalls+0x59/0xa0 init/main.c:1460
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1692
kernel_init+0x1d/0x1d0 init/main.c:1582
page last free pid 10 tgid 10 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1433 [inline]
__free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
vfree+0x25a/0x400 mm/vmalloc.c:3479
delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
process_one_work kernel/workqueue.c:3275 [inline]
process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
kthread+0x388/0x470 kernel/kthread.c:467
ret_from_fork+0x51e/0xb90 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:
ffff88816d32af00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88816d32af80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88816d32b000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88816d32b080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88816d32b100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

***

WARNING in pt_range_walk

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 857fa8f2a5b184c206c703a3d9ce05cea683cfed
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/932ed80d-9fb1-4c99-8096-4b7a9324bb7c/config
syz repro: https://ci.syzbot.org/findings/e7c203a3-133f-4435-b9ed-ee292b6685fe/syz_repro

------------[ cut here ]------------
next_addr < vma->vm_start || next_addr >= vma->vm_end
WARNING: mm/pagewalk.c:1052 at pt_range_walk+0x145/0x35f0 mm/pagewalk.c:1052, CPU#1: syz.1.18/6005
Modules linked in:
CPU: 1 UID: 0 PID: 6005 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:pt_range_walk+0x145/0x35f0 mm/pagewalk.c:1052
Code: df e8 9f 1a 15 00 49 89 dc 48 8b 1b 4c 89 ff 48 89 de e8 7e a5 aa ff 49 39 df 4c 89 b4 24 38 01 00 00 73 14 e8 0c a3 aa ff 90 <0f> 0b 90 41 be 01 00 00 00 e9 e5 21 00 00 49 8d 5c 24 08 48 89 d8
RSP: 0018:ffffc90003a279a0 EFLAGS: 00010293
RAX: ffffffff821b140c RBX: 0000200001000000 RCX: ffff8881027a5700
RDX: 0000000000000000 RSI: 0000200001000000 RDI: 0000200001000000
RBP: ffffc90003a27bb0 R08: 00000000000000ff R09: 0000000000000003
R10: 0000000000000002 R11: 0000000000000000 R12: ffff888105317380
R13: dffffc0000000000 R14: 1ffff92000744f60 R15: 0000200001000000
FS: 00007f0ccbd736c0(0000) GS:ffff8882a9467000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0ccb04edd5 CR3: 0000000115dba000 CR4: 00000000000006f0
Call Trace:
<TASK>
pagemap_scan_walk fs/proc/task_mmu.c:2479 [inline]
do_pagemap_scan fs/proc/task_mmu.c:2573 [inline]
do_pagemap_cmd+0xfd5/0x2600 fs/proc/task_mmu.c:2869
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0ccaf9c819
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:00007f0ccbd73028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0ccb215fa0 RCX: 00007f0ccaf9c819
RDX: 0000200000000100 RSI: 00000000c0606610 RDI: 0000000000000003
RBP: 00007f0ccb032c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0ccb216038 R14: 00007f0ccb215fa0 R15: 00007ffd9c7ebb48
</TASK>

***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com

---
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