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    Subject[PATCH 5.12 032/700] ntfs: fix validity check for file name attribute
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    From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>

    commit d98e4d95411bbde2220a7afa38dcc9c14d71acbe upstream.

    When checking the file name attribute, we want to ensure that it fits
    within the bounds of ATTR_RECORD. To do this, we should check that (attr
    record + file name offset + file name length) < (attr record + attr record
    length).

    However, the original check did not include the file name offset in the
    calculation. This means that corrupted on-disk metadata might not caught
    by the incorrect file name check, and lead to an invalid memory access.

    An example can be seen in the crash report of a memory corruption error
    found by Syzbot:
    https://syzkaller.appspot.com/bug?id=a1a1e379b225812688566745c3e2f7242bffc246

    Adding the file name offset to the validity check fixes this error and
    passes the Syzbot reproducer test.

    Link: https://lkml.kernel.org/r/20210614050540.289494-1-desmondcheongzx@gmail.com
    Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
    Reported-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
    Tested-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
    Acked-by: Anton Altaparmakov <anton@tuxera.com>
    Cc: Shuah Khan <skhan@linuxfoundation.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ntfs/inode.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/fs/ntfs/inode.c
    +++ b/fs/ntfs/inode.c
    @@ -477,7 +477,7 @@ err_corrupt_attr:
    }
    file_name_attr = (FILE_NAME_ATTR*)((u8*)attr +
    le16_to_cpu(attr->data.resident.value_offset));
    - p2 = (u8*)attr + le32_to_cpu(attr->data.resident.value_length);
    + p2 = (u8 *)file_name_attr + le32_to_cpu(attr->data.resident.value_length);
    if (p2 < (u8*)attr || p2 > p)
    goto err_corrupt_attr;
    /* This attribute is ok, but is it in the $Extend directory? */

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