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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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fs/ntfs3: prevent uninitialized lcn caused by zero len

syzbot reported a uninit-value in ntfs_iomap_begin [1].

Since runs was not touched yet, run_lookup_entry() immediately fails
and returns false, which makes the value of "*len" 0.
Simultaneously, the new value and err value are also 0, causing the
logic in attr_data_get_block_locked() to jump directly to ok, ultimately
resulting in *lcn being triggered before it is set [1].

In ntfs_iomap_begin(), the check for a 0 value in clen is moved forward
to before updating lcn to avoid this [1].

[1]
BUG: KMSAN: uninit-value in ntfs_iomap_begin+0x8c0/0x1460 fs/ntfs3/inode.c:825
ntfs_iomap_begin+0x8c0/0x1460 fs/ntfs3/inode.c:825
iomap_iter+0x9b7/0x1540 fs/iomap/iter.c:110

Local variable lcn created at:
ntfs_iomap_begin+0x15d/0x1460 fs/ntfs3/inode.c:786

Fixes: 10d7c95af043 ("fs/ntfs3: add delayed-allocation (delalloc) support")
Reported-by: syzbot+7be88937363ac7ab7bb0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7be88937363ac7ab7bb0
Tested-by: syzbot+7be88937363ac7ab7bb0@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

authored by

Edward Adam Davis and committed by
Konstantin Komarov e98266e8 48d9b57b

+5 -5
+5 -5
fs/ntfs3/inode.c
··· 827 827 return err; 828 828 } 829 829 830 + if (!clen) { 831 + /* broken file? */ 832 + return -EINVAL; 833 + } 834 + 830 835 if (lcn == EOF_LCN) { 831 836 /* request out of file. */ 832 837 if (flags & IOMAP_REPORT) { ··· 863 858 iomap->offset = 0; 864 859 iomap->length = clen; /* resident size in bytes. */ 865 860 return 0; 866 - } 867 - 868 - if (!clen) { 869 - /* broken file? */ 870 - return -EINVAL; 871 861 } 872 862 873 863 iomap->bdev = inode->i_sb->s_bdev;