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    Subject[PATCH 4.14 202/315] fscrypt: dont ignore minor_hash when hash is 0
    Date
    From: Eric Biggers <ebiggers@google.com>

    commit 77f30bfcfcf484da7208affd6a9e63406420bf91 upstream.

    When initializing a no-key name, fscrypt_fname_disk_to_usr() sets the
    minor_hash to 0 if the (major) hash is 0.

    This doesn't make sense because 0 is a valid hash code, so we shouldn't
    ignore the filesystem-provided minor_hash in that case. Fix this by
    removing the special case for 'hash == 0'.

    This is an old bug that appears to have originated when the encryption
    code in ext4 and f2fs was moved into fs/crypto/. The original ext4 and
    f2fs code passed the hash by pointer instead of by value. So
    'if (hash)' actually made sense then, as it was checking whether a
    pointer was NULL. But now the hashes are passed by value, and
    filesystems just pass 0 for any hashes they don't have. There is no
    need to handle this any differently from the hashes actually being 0.

    It is difficult to reproduce this bug, as it only made a difference in
    the case where a filename's 32-bit major hash happened to be 0.
    However, it probably had the largest chance of causing problems on
    ubifs, since ubifs uses minor_hash to do lookups of no-key names, in
    addition to using it as a readdir cookie. ext4 only uses minor_hash as
    a readdir cookie, and f2fs doesn't use minor_hash at all.

    Fixes: 0b81d0779072 ("fs crypto: move per-file encryption from f2fs tree to fs/crypto")
    Cc: <stable@vger.kernel.org> # v4.6+
    Link: https://lore.kernel.org/r/20210527235236.2376556-1-ebiggers@kernel.org
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/crypto/fname.c | 9 ++-------
    1 file changed, 2 insertions(+), 7 deletions(-)

    --- a/fs/crypto/fname.c
    +++ b/fs/crypto/fname.c
    @@ -304,13 +304,8 @@ int fscrypt_fname_disk_to_usr(struct ino
    oname->name);
    return 0;
    }
    - if (hash) {
    - digested_name.hash = hash;
    - digested_name.minor_hash = minor_hash;
    - } else {
    - digested_name.hash = 0;
    - digested_name.minor_hash = 0;
    - }
    + digested_name.hash = hash;
    + digested_name.minor_hash = minor_hash;
    memcpy(digested_name.digest,
    FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
    FSCRYPT_FNAME_DIGEST_SIZE);

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