[moderation] [kernel?] KCSAN: data-race in _copy_from_iter / copy_mc_to_kernel

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c22e26bd0906 Merge tag 'landlock-7.0-rc1' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14183e5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7cbb341929b72cb5
dashboard link: https://syzkaller.appspot.com/bug?extid=bfef223fdab1b492ca23
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [b...@alien8.de dave....@linux.intel.com h...@zytor.com linux-...@vger.kernel.org mi...@redhat.com tg...@kernel.org x...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0a97430abcaa/disk-c22e26bd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8ec5adec5713/vmlinux-c22e26bd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d7da85ac0b56/bzImage-c22e26bd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bfef22...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_from_iter / copy_mc_to_kernel

read to 0xffff88810bdab000 of 4096 bytes by task 4327 on cpu 0:
instrument_memcpy_before include/linux/instrumented.h:165 [inline]
copy_mc_to_kernel+0x43/0xb0 arch/x86/lib/copy_mc.c:74
copy_mc_user_highpage include/linux/highmem.h:345 [inline]
copy_present_page mm/memory.c:1063 [inline]
copy_present_ptes mm/memory.c:1169 [inline]
copy_pte_range mm/memory.c:1304 [inline]
copy_pmd_range mm/memory.c:1392 [inline]
copy_pud_range mm/memory.c:1429 [inline]
copy_p4d_range mm/memory.c:1453 [inline]
copy_page_range+0x1aad/0x3cf0 mm/memory.c:1539
dup_mmap+0x852/0xf00 mm/mmap.c:1827
dup_mm kernel/fork.c:1530 [inline]
copy_mm+0x119/0x370 kernel/fork.c:1582
copy_process+0xe22/0x20c0 kernel/fork.c:2223
kernel_clone+0x16b/0x5b0 kernel/fork.c:2654
__do_sys_clone kernel/fork.c:2795 [inline]
__se_sys_clone kernel/fork.c:2779 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2779
x64_sys_call+0x1222/0x3020 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff88810bdab000 of 4096 bytes by task 4324 on cpu 1:
instrument_copy_from_user_before include/linux/instrumented.h:130 [inline]
copy_from_user_iter lib/iov_iter.c:66 [inline]
iterate_ubuf include/linux/iov_iter.h:30 [inline]
iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
__copy_from_iter lib/iov_iter.c:261 [inline]
_copy_from_iter+0x106/0xea0 lib/iov_iter.c:272
copy_page_from_iter+0x178/0x2a0 lib/iov_iter.c:434
process_vm_rw_pages mm/process_vm_access.c:43 [inline]
process_vm_rw_single_vec mm/process_vm_access.c:118 [inline]
process_vm_rw_core mm/process_vm_access.c:216 [inline]
process_vm_rw+0x6ad/0x9c0 mm/process_vm_access.c:284
__do_sys_process_vm_writev mm/process_vm_access.c:304 [inline]
__se_sys_process_vm_writev mm/process_vm_access.c:299 [inline]
__x64_sys_process_vm_writev+0x78/0x90 mm/process_vm_access.c:299
x64_sys_call+0x1592/0x3020 arch/x86/include/generated/asm/syscalls_64.h:312
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4324 Comm: syz.2.249 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================


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