linux-hardening - Re: [PATCH] fscrypt: Replace 1-element array with flexible array

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Message-ID: <20230522230206.GA3187780@google.com>
Date:   Mon, 22 May 2023 23:02:06 +0000
From:   Eric Biggers <ebiggers@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] fscrypt: Replace 1-element array with flexible array

On Mon, May 22, 2023 at 02:39:28PM -0700, Kees Cook wrote:
> In the future, we can add annotations for the flexible array member
> "encrypted_path" to have a size determined by the "len" member.

That seems unlikely, as 'struct fscrypt_symlink_data' is an on-disk data
structure.  The "len" field does not necessarily use CPU endianness, and before
being validated it might be greater than the size of the allocated space.

I agree that it should use a flex array (and thanks for catching this one that I
had forgotten about...), but the above explanation seems wrong.

- Eric