[syzbot] [ntfs3?] KMSAN: uninit-value in ni_seek_data_or_hole

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cca95436be15 Merge tag 'phy-fixes-7.1' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10e36d6a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=91978e795dcd971b
dashboard link: https://syzkaller.appspot.com/bug?extid=c2cfe997245202e46f10
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=147dad96580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140c2cec580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fb3ceeccf5bc/disk-cca95436.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/af588c0672f1/vmlinux-cca95436.xz
kernel image: https://storage.googleapis.com/syzbot-assets/beac806b38fd/bzImage-cca95436.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/7ca9c62c48ea/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c2cfe9...@syzkaller.appspotmail.com

ntfs3(loop0): Mark volume as dirty due to NTFS errors
ntfs3(loop0): ino=1a, mi_enum_attr
ntfs3(loop0): ino=1a, mi_enum_attr
ntfs3(loop0): Failed to initialize $Extend/$Reparse.
=====================================================
BUG: KMSAN: uninit-value in ni_seek_data_or_hole+0x24f/0x5f0 fs/ntfs3/frecord.c:2862
ni_seek_data_or_hole+0x24f/0x5f0 fs/ntfs3/frecord.c:2862
ntfs_llseek+0x22a/0x4a0 fs/ntfs3/file.c:1530
vfs_llseek fs/read_write.c:391 [inline]
ksys_lseek fs/read_write.c:404 [inline]
__do_sys_lseek fs/read_write.c:414 [inline]
__se_sys_lseek fs/read_write.c:412 [inline]
__x64_sys_lseek+0x29d/0x460 fs/read_write.c:412
x64_sys_call+0x3004/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:9
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
ni_seek_data_or_hole+0x248/0x5f0 fs/ntfs3/frecord.c:2862
ntfs_llseek+0x22a/0x4a0 fs/ntfs3/file.c:1530
vfs_llseek fs/read_write.c:391 [inline]
ksys_lseek fs/read_write.c:404 [inline]
__do_sys_lseek fs/read_write.c:414 [inline]
__se_sys_lseek fs/read_write.c:412 [inline]
__x64_sys_lseek+0x29d/0x460 fs/read_write.c:412
x64_sys_call+0x3004/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:9
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable lcn created at:
ni_seek_data_or_hole+0x72/0x5f0 fs/ntfs3/frecord.c:2851
ntfs_llseek+0x22a/0x4a0 fs/ntfs3/file.c:1530

CPU: 0 UID: 0 PID: 5901 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
=====================================================


---
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[Edward Adam Davis]

#syz test

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 7b035da63c12..d511b6a75ae8 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -2859,6 +2859,11 @@ loff_t ni_seek_data_or_hole(struct ntfs_inode *ni, loff_t offset, bool data)
return err;
}

+ if (!clen) {
+ /* Corrupted file. */
+ return -EINVAL;
+ }
+
if (lcn == RESIDENT_LCN) {
/* clen - resident size in bytes. clen == ni->vfs_inode.i_size */
if (offset >= clen) {
@@ -2909,10 +2914,6 @@ loff_t ni_seek_data_or_hole(struct ntfs_inode *ni, loff_t offset, bool data)
}
}

- if (!clen) {
- /* Corrupted file. */
- return -EINVAL;
- }
}
}

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
lost connection to test machine



Tested on:

commit: e8c2f9fd Merge tag 'for-7.1/hpfs-fixes' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=103f5aa6580000

kernel config: https://syzkaller.appspot.com/x/.config?x=91978e795dcd971b
dashboard link: https://syzkaller.appspot.com/bug?extid=c2cfe997245202e46f10
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=10119aec580000

[Edward Adam Davis]

The target VCN being sought was not found within runs[0], causing
run_lookup() to return false. This causes run_lookup_entry() to return
false, which in turn results in a len value of 0, and the new parameter
passed to attr_data_get_block() is NULL. Collectively, these factors
ultimately cause attr_data_get_block_locked() to exit prematurely without
initializing lcn, thereby triggering [1].

To prevent [1], the clen check within ni_seek_data_or_hole() has been
moved to occur before the lcn check.

[1]

BUG: KMSAN: uninit-value in ni_seek_data_or_hole+0x24f/0x5f0 fs/ntfs3/frecord.c:2862
ni_seek_data_or_hole+0x24f/0x5f0 fs/ntfs3/frecord.c:2862
ntfs_llseek+0x22a/0x4a0 fs/ntfs3/file.c:1530
vfs_llseek fs/read_write.c:391 [inline]

Fixes: c61326967728 ("fs/ntfs3: implement llseek SEEK_DATA/SEEK_HOLE by scanning data runs")
Reported-by: syzbot+c2cfe9...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c2cfe997245202e46f10
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/ntfs3/frecord.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--
2.43.0