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Date: Tue, 13 Mar 2018 12:39:03 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Tycho Andersen <tycho@...ho.ws>
Cc: David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 2/2] dh key: get rid of stack array allocation
Quoting Tycho Andersen (tycho@...ho.ws):
> Similarly to the previous patch, we would like to get rid of stack
> allocated arrays: https://lkml.org/lkml/2018/3/7/621
>
> In this case, we can also use a malloc style approach to free the temporary
> buffer, being careful to also use kzfree to free them (indeed, at least one
> of these has a memzero_explicit, but it seems like maybe they both
> should?).
>
> Signed-off-by: Tycho Andersen <tycho@...ho.ws>
> CC: David Howells <dhowells@...hat.com>
> CC: James Morris <jmorris@...ei.org>
> CC: "Serge E. Hallyn" <serge@...lyn.com>
Acked-by: Serge Hallyn <serge@...lyn.com>
for both, thanks.
> ---
> security/keys/dh.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/security/keys/dh.c b/security/keys/dh.c
> index d1ea9f325f94..f02261b24759 100644
> --- a/security/keys/dh.c
> +++ b/security/keys/dh.c
> @@ -162,19 +162,27 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
> goto err;
>
> if (zlen && h) {
> - u8 tmpbuffer[h];
> + u8 *tmpbuffer;
> size_t chunk = min_t(size_t, zlen, h);
> - memset(tmpbuffer, 0, chunk);
> +
> + err = -ENOMEM;
> + tmpbuffer = kzalloc(chunk, GFP_KERNEL);
> + if (!tmpbuffer)
> + goto err;
>
> do {
> err = crypto_shash_update(desc, tmpbuffer,
> chunk);
> - if (err)
> + if (err) {
> + kzfree(tmpbuffer);
> goto err;
> + }
>
> zlen -= chunk;
> chunk = min_t(size_t, zlen, h);
> } while (zlen);
> +
> + kzfree(tmpbuffer);
> }
>
> if (src && slen) {
> @@ -184,13 +192,20 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
> }
>
> if (dlen < h) {
> - u8 tmpbuffer[h];
> + u8 *tmpbuffer;
> +
> + err = -ENOMEM;
> + tmpbuffer = kzalloc(h, GFP_KERNEL);
> + if (!tmpbuffer)
> + goto err;
>
> err = crypto_shash_final(desc, tmpbuffer);
> - if (err)
> + if (err) {
> + kzfree(tmpbuffer);
> goto err;
> + }
> memcpy(dst, tmpbuffer, dlen);
> - memzero_explicit(tmpbuffer, h);
> + kzfree(tmpbuffer);
> return 0;
> } else {
> err = crypto_shash_final(desc, dst);
> --
> 2.15.1
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