[syzbot] [iommu?] KMSAN: uninit-value in pfn_reader_next

[syzbot]

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+df2807...@syzkaller.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
=====================================================


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***

Subject: [PATCH] iommufd: Initialize pfn_reader in iopt_area_fill_domains()
Author: karti...@gmail.com


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

KMSAN reported an uninitialized value in batch_add_pfn_num() when
accessing batch->npfns[] and batch->pfns[] arrays. This occurs because
struct pfn_reader pfns was declared without initialization, leaving
the embedded pfn_batch structure and its arrays uninitialized.

Initialize pfns to zero to ensure all fields and embedded structures
start in a known state.

Reported-by: syzbot+df2807...@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
drivers/iommu/iommufd/pages.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c
index dbe51ecb9a20..a07373cf013c 100644
--- a/drivers/iommu/iommufd/pages.c
+++ b/drivers/iommu/iommufd/pages.c
@@ -1897,7 +1897,7 @@ int iopt_area_fill_domains(struct iopt_area *area, struct iopt_pages *pages)
unsigned long done_all_end_index;
struct iommu_domain *domain;
unsigned long unmap_index;
- struct pfn_reader pfns;
+ struct pfn_reader pfns = {};
unsigned long index;
int rc;

--
2.43.0