[syzbot] [fs?] [mm?] KMSAN: kernel-infoleak in hugetlbfs_read_iter

[syzbot <syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    439fc29dfd3b Merge tag 'drm-fixes-2025-11-09' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c7517c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cbf50e713aaa5cb0
dashboard link: https://syzkaller.appspot.com/bug?extid=f64019ba229e3a5c411b
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=107f3084580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10634b42580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cfc76859b0d7/disk-439fc29d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1a4aa2e08e02/vmlinux-439fc29d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/24591c797483/bzImage-439fc29d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
BUG: KMSAN: kernel-infoleak in iterate_iovec include/linux/iov_iter.h:52 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:330 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x4e4/0x33f0 lib/iov_iter.c:185
 instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_iovec include/linux/iov_iter.h:52 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x4e4/0x33f0 lib/iov_iter.c:185
 copy_page_to_iter+0x482/0x910 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 hugetlbfs_read_iter+0x6cd/0xe10 fs/hugetlbfs/inode.c:281
 do_iter_readv_writev+0x9e1/0xc20 fs/read_write.c:-1
 vfs_readv+0x34a/0xf30 fs/read_write.c:1018
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x2a3/0x510 fs/read_write.c:1174
 x64_sys_call+0x3064/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:296
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 __alloc_frozen_pages_noprof+0x689/0xf00 mm/page_alloc.c:5206
 alloc_buddy_hugetlb_folio mm/hugetlb.c:1944 [inline]
 only_alloc_fresh_hugetlb_folio+0x2b0/0x1280 mm/hugetlb.c:1984
 alloc_fresh_hugetlb_folio mm/hugetlb.c:2003 [inline]
 alloc_surplus_hugetlb_folio+0x178/0x5c0 mm/hugetlb.c:2223
 gather_surplus_pages mm/hugetlb.c:2415 [inline]
 hugetlb_acct_memory+0x759/0x2420 mm/hugetlb.c:5331
 hugetlb_reserve_pages+0x10d1/0x26f0 mm/hugetlb.c:7347
 memfd_alloc_folio+0x20a/0x7b0 mm/memfd.c:90
 memfd_pin_folios+0x10b3/0x16a0 mm/gup.c:3523
 udmabuf_pin_folios drivers/dma-buf/udmabuf.c:337 [inline]
 udmabuf_create+0x1256/0x1ed0 drivers/dma-buf/udmabuf.c:434
 udmabuf_ioctl_create drivers/dma-buf/udmabuf.c:486 [inline]
 udmabuf_ioctl+0x2eb/0x5b0 drivers/dma-buf/udmabuf.c:517
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0x23c/0x400 fs/ioctl.c:583
 __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:583
 x64_sys_call+0x1cbc/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Bytes 0-5 of 6 are uninitialized
Memory access of size 6 starts at ffff88804480000f
Data copied to user address 0000200000000080

CPU: 0 UID: 0 PID: 6052 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
=====================================================


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