Re: [PATCH] crypto: chacha20poly1305 - validate the digest size

[Herbert Xu <herbert@gondor.apana.org.au>]

On Mon, Dec 11, 2017 at 12:15:17PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> If the rfc7539 template was instantiated with a hash algorithm with
> digest size larger than 16 bytes (POLY1305_DIGEST_SIZE), then the digest
> overran the 'tag' buffer in 'struct chachapoly_req_ctx', corrupting the
> subsequent memory, including 'cryptlen'.  This caused a crash during
> crypto_skcipher_decrypt().
> 
> Fix it by, when instantiating the template, requiring that the
> underlying hash algorithm has the digest size expected for Poly1305.
> 
> Reproducer:
> 
>     #include <linux/if_alg.h>
>     #include <sys/socket.h>
>     #include <unistd.h>
> 
>     int main()
>     {
>             int algfd, reqfd;
>             struct sockaddr_alg addr = {
>                     .salg_type = "aead",
>                     .salg_name = "rfc7539(chacha20,sha256)",
>             };
>             unsigned char buf[32] = { 0 };
> 
>             algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
>             bind(algfd, (void *)&addr, sizeof(addr));
>             setsockopt(algfd, SOL_ALG, ALG_SET_KEY, buf, sizeof(buf));
>             reqfd = accept(algfd, 0, 0);
>             write(reqfd, buf, 16);
>             read(reqfd, buf, 16);
>     }
> 
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Fixes: 71ebc4d1b27d ("crypto: chacha20poly1305 - Add a ChaCha20-Poly1305 AEAD construction, RFC7539")
> Cc: <stable@vger.kernel.org> # v4.2+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
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