[moderation] [fs?] KASAN: stack-out-of-bounds Read in unwind_next_frame (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4a26e7032d7d Merge tag 'core-bugs-2025-12-01' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=166fe4c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cabbc708f0a470fb
dashboard link: https://syzkaller.appspot.com/bug?extid=d11a51df2898c594fa4a
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/41d09ea4104d/disk-4a26e703.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e8c0f32d0475/vmlinux-4a26e703.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f19b39e18b64/bzImage-4a26e703.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d11a51...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in user_mode arch/x86/include/asm/ptrace.h:214 [inline]
BUG: KASAN: stack-out-of-bounds in unwind_next_frame+0x1cb0/0x2390 arch/x86/kernel/unwind_orc.c:482
Read of size 2 at addr ffffc900047a78d0 by task syz.2.5242/24863

CPU: 0 UID: 0 PID: 24863 Comm: syz.2.5242 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
user_mode arch/x86/include/asm/ptrace.h:214 [inline]
unwind_next_frame+0x1cb0/0x2390 arch/x86/kernel/unwind_orc.c:482
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save_tsk+0x15f/0x200 kernel/stacktrace.c:150
proc_pid_stack+0x12c/0x1f0 fs/proc/base.c:492
proc_single_show+0xee/0x190 fs/proc/base.c:812
traverse+0x1ee/0x580 fs/seq_file.c:111
seq_read_iter+0xd08/0xe20 fs/seq_file.c:195
seq_read+0x369/0x480 fs/seq_file.c:162
vfs_read+0x200/0xa30 fs/read_write.c:570
ksys_pread64 fs/read_write.c:763 [inline]
__do_sys_pread64 fs/read_write.c:771 [inline]
__se_sys_pread64 fs/read_write.c:768 [inline]
__x64_sys_pread64+0x193/0x220 fs/read_write.c:768
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbb08b8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbb099b5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007fbb08de5fa0 RCX: 00007fbb08b8f749
RDX: 0000000000001005 RSI: 0000200000001580 RDI: 0000000000000003
RBP: 00007fbb08c13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000a R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbb08de6038 R14: 00007fbb08de5fa0 R15: 00007ffe365751b8
</TASK>

The buggy address belongs to a 8-page vmalloc region starting at 0xffffc900047a0000 allocated at copy_process+0x54b/0x3c10 kernel/fork.c:2012
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888066ad5640 pfn:0x66ad5
memcg:ffff88802a98eb02
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: ffff888066ad5640 0000000000000000 00000001ffffffff ffff88802a98eb02
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x2dc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO|__GFP_NOWARN), pid 24834, tgid 24834 (syz.9.5237), ts 2201704750630, free_ts 2200964256248
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x234/0x290 mm/page_alloc.c:1845
prep_new_page mm/page_alloc.c:1853 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3879
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5178
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
vm_area_alloc_pages mm/vmalloc.c:3647 [inline]
__vmalloc_area_node mm/vmalloc.c:3724 [inline]
__vmalloc_node_range_noprof+0x96c/0x12d0 mm/vmalloc.c:3897
__vmalloc_node_noprof+0xc2/0x110 mm/vmalloc.c:3960
alloc_thread_stack_node kernel/fork.c:311 [inline]
dup_task_struct+0x3d4/0x830 kernel/fork.c:881
copy_process+0x54b/0x3c10 kernel/fork.c:2012
kernel_clone+0x21e/0x820 kernel/fork.c:2610
__do_sys_clone3 kernel/fork.c:2912 [inline]
__se_sys_clone3+0x256/0x2d0 kernel/fork.c:2891
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 16361 tgid 16361 stack trace:
create_dummy_stack mm/page_owner.c:94 [inline]
register_dummy_stack+0x89/0xe0 mm/page_owner.c:100
init_page_owner+0x2e/0x620 mm/page_owner.c:118
invoke_init_callbacks mm/page_ext.c:148 [inline]
page_ext_init+0x511/0x550 mm/page_ext.c:486
mm_core_init+0x56/0x70 mm/mm_init.c:2721

Memory state around the buggy address:
ffffc900047a7780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900047a7800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900047a7880: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f2 00 00
^
ffffc900047a7900: 00 f2 f2 f2 f2 f2 00 f2 f2 f2 00 00 f3 f3 f3 f3
ffffc900047a7980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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