linux-kernel - [syzbot] [iommu?] KMSAN: uninit-value in pfn_reader

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Message-ID: <69746a86.050a0220.226181.0002.GAE@google.com>
Date: Fri, 23 Jan 2026 22:45:26 -0800
From: syzbot <syzbot+df28076a30d726933015@...kaller.appspotmail.com>
To: iommu@...ts.linux.dev, jgg@...pe.ca, joro@...tes.org, kevin.tian@...el.com, 
	linux-kernel@...r.kernel.org, robin.murphy@....com, 
	syzkaller-bugs@...glegroups.com, will@...nel.org
Subject: [syzbot] [iommu?] KMSAN: uninit-value in pfn_reader_next

Hello,

syzbot found the following issue on:

HEAD commit:    c072629f05d7 Merge tag 'v6.19-p4' of git://git.kernel.org/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1716005a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=df28076a30d726933015
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1436b79a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15a63d22580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b6b938ba4a72/disk-c072629f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bb1384b011b2/vmlinux-c072629f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1dd4bb2f206e/bzImage-c072629f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df28076a30d726933015@...kaller.appspotmail.com

iommufd_mock iommufd_mock0: Adding to iommu group 0
=====================================================
BUG: KMSAN: uninit-value in batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
BUG: KMSAN: uninit-value in batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]
BUG: KMSAN: uninit-value in batch_from_pages drivers/iommu/iommufd/pages.c:658 [inline]
BUG: KMSAN: uninit-value in pfn_reader_fill_span drivers/iommu/iommufd/pages.c:1220 [inline]
BUG: KMSAN: uninit-value in pfn_reader_next+0x1d5a/0x3e50 drivers/iommu/iommufd/pages.c:1247
 batch_add_pfn_num drivers/iommu/iommufd/pages.c:365 [inline]
 batch_add_pfn drivers/iommu/iommufd/pages.c:398 [inline]
 batch_from_pages drivers/iommu/iommufd/pages.c:658 [inline]
 pfn_reader_fill_span drivers/iommu/iommufd/pages.c:1220 [inline]
 pfn_reader_next+0x1d5a/0x3e50 drivers/iommu/iommufd/pages.c:1247
 pfn_reader_first+0xbcf/0xee0 drivers/iommu/iommufd/pages.c:1354
 iopt_area_fill_domains+0x202/0x1590 drivers/iommu/iommufd/pages.c:1917
 iopt_fill_domains_pages drivers/iommu/iommufd/io_pagetable.c:359 [inline]
 iopt_map_pages+0x1ba5/0x2130 drivers/iommu/iommufd/io_pagetable.c:387
 iopt_map_common+0x224/0x610 drivers/iommu/iommufd/io_pagetable.c:425
 iopt_map_user_pages+0x148/0x1c0 drivers/iommu/iommufd/io_pagetable.c:466
 iommufd_ioas_map+0x6a2/0x9b0 drivers/iommu/iommufd/ioas.c:270
 iommufd_fops_ioctl+0x82a/0x9e0 drivers/iommu/iommufd/main.c:533
 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+0x18a7/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable pfns created at:
 iopt_area_fill_domains+0x5c/0x1590 drivers/iommu/iommufd/pages.c:1900
 iopt_fill_domains_pages drivers/iommu/iommufd/io_pagetable.c:359 [inline]
 iopt_map_pages+0x1ba5/0x2130 drivers/iommu/iommufd/io_pagetable.c:387

CPU: 0 UID: 0 PID: 6065 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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If the report is already addressed, let syzbot know by replying with:
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