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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Thu, 6 Feb 2020 11:47:14 +0000
Message-ID: <CAKv+Gu8Zh3XmZVySHxHNX4Tgh22JFd0C7mJUGz5YBSEhxfCF6g@mail.gmail.com>
Subject: Re: [PATCH stable] crypto: chacha20poly1305 - prevent integer
 overflow on large input
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
        stable <stable@vger.kernel.org>
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On Thu, 6 Feb 2020 at 11:42, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> This code assigns src_len (size_t) to sl (int), which causes problems
> when src_len is very large. Probably nobody in the kernel should be
> passing this much data to chacha20poly1305 all in one go anyway, so I
> don't think we need to change the algorithm or introduce larger types
> or anything. But we should at least error out early in this case and
> print a warning so that we get reports if this does happen and can look
> into why anybody is possibly passing it that much data or if they're
> accidently passing -1 or similar.
>
> Fixes: d95312a3ccc0 ("crypto: lib/chacha20poly1305 - reimplement crypt_from_sg() routine")
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: stable@vger.kernel.org # 5.5+
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  lib/crypto/chacha20poly1305.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/lib/crypto/chacha20poly1305.c b/lib/crypto/chacha20poly1305.c
> index 6d83cafebc69..ad0699ce702f 100644
> --- a/lib/crypto/chacha20poly1305.c
> +++ b/lib/crypto/chacha20poly1305.c
> @@ -235,6 +235,9 @@ bool chacha20poly1305_crypt_sg_inplace(struct scatterlist *src,
>                 __le64 lens[2];
>         } b __aligned(16);
>
> +       if (WARN_ON(src_len > INT_MAX))
> +               return false;
> +
>         chacha_load_key(b.k, key);
>
>         b.iv[0] = 0;
> --
> 2.25.0
>