From: Eric Biggers <ebiggers3@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
Giovanni Cabiddu <giovanni.cabiddu@intel.com>,
Arnd Bergmann <arnd@arndb.de>, Eric Biggers <ebiggers@google.com>,
Mike Snitzer <snitzer@redhat.com>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
qat-linux@intel.com, linux-kernel@vger.kernel.org,
dm-devel@redhat.com, linux-crypto@vger.kernel.org,
Lars Persson <larper@axis.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
"David S. Miller" <davem@davemloft.net>,
Alasdair Kergon <agk@redhat.com>, Rabin Vincent <rabinv@axis.com>
Subject: Re: [dm-devel] [PATCH v3 9/9] crypto: shash: Remove VLA usage in unaligned hashing
Date: Sat, 30 Jun 2018 00:03:01 -0700 [thread overview]
Message-ID: <20180630070301.GA1706@sol.localdomain> (raw)
In-Reply-To: <20180629002843.31095-10-keescook@chromium.org>
On Thu, Jun 28, 2018 at 05:28:43PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this uses
> the newly defined max alignment to perform unaligned hashing to avoid
> VLAs, and drops the helper function while adding sanity checks on the
> resulting buffer sizes. Additionally, the __aligned_largest macro is
> removed since this helper was the only user.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> crypto/shash.c | 19 ++++++++-----------
> include/linux/compiler-gcc.h | 1 -
> 2 files changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/crypto/shash.c b/crypto/shash.c
> index ab6902c6dae7..8081c5e03770 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -73,13 +73,6 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
> }
> EXPORT_SYMBOL_GPL(crypto_shash_setkey);
>
> -static inline unsigned int shash_align_buffer_size(unsigned len,
> - unsigned long mask)
> -{
> - typedef u8 __aligned_largest u8_aligned;
> - return len + (mask & ~(__alignof__(u8_aligned) - 1));
> -}
> -
> static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,
> unsigned int len)
> {
> @@ -88,11 +81,13 @@ static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,
> unsigned long alignmask = crypto_shash_alignmask(tfm);
> unsigned int unaligned_len = alignmask + 1 -
> ((unsigned long)data & alignmask);
> - u8 ubuf[shash_align_buffer_size(unaligned_len, alignmask)]
> - __aligned_largest;
> + u8 ubuf[MAX_ALGAPI_ALIGNMASK + 1];
> u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
> int err;
>
> + if (WARN_ON(buf + unaligned_len > ubuf + sizeof(ubuf)))
> + return -EINVAL;
> +
How is 'ubuf' guaranteed to be large enough? You removed the __aligned
attribute, so 'ubuf' can have any alignment. So the aligned pointer 'buf' may
be as high as '&ubuf[alignmask]'. Then, up to 'alignmask' bytes of data will be
copied into 'buf'... resulting in up to '2 * alignmask' bytes needed in 'ubuf'.
But you've only guaranteed 'alignmask + 1' bytes.
> if (unaligned_len > len)
> unaligned_len = len;
>
> @@ -124,11 +119,13 @@ static int shash_final_unaligned(struct shash_desc *desc, u8 *out)
> unsigned long alignmask = crypto_shash_alignmask(tfm);
> struct shash_alg *shash = crypto_shash_alg(tfm);
> unsigned int ds = crypto_shash_digestsize(tfm);
> - u8 ubuf[shash_align_buffer_size(ds, alignmask)]
> - __aligned_largest;
> + u8 ubuf[SHASH_MAX_DIGESTSIZE];
> u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
> int err;
>
> + if (WARN_ON(buf + ds > ubuf + sizeof(ubuf)))
> + return -EINVAL;
> +
Similar problem here. Wouldn't 'ubuf' need to be of size 'alignmask + ds'?
> err = shash->final(desc, buf);
> if (err)
> goto out;
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index f1a7492a5cc8..1f1cdef36a82 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -125,7 +125,6 @@
> */
> #define __pure __attribute__((pure))
> #define __aligned(x) __attribute__((aligned(x)))
> -#define __aligned_largest __attribute__((aligned))
> #define __printf(a, b) __attribute__((format(printf, a, b)))
> #define __scanf(a, b) __attribute__((format(scanf, a, b)))
> #define __attribute_const__ __attribute__((__const__))
> --
> 2.17.1
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
next prev parent reply other threads:[~2018-06-30 7:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-29 0:28 [PATCH v3 0/9] Crypto: Remove VLA usage (part 1) Kees Cook
2018-06-29 0:28 ` [PATCH v3 1/9] crypto: xcbc: Remove VLA usage Kees Cook
2018-06-29 0:28 ` [PATCH v3 2/9] crypto: cbc: " Kees Cook
2018-06-29 0:28 ` [PATCH v3 3/9] crypto: shash: " Kees Cook
2018-06-29 0:28 ` [PATCH v3 4/9] dm integrity: " Kees Cook
2018-06-29 20:43 ` Arnd Bergmann
2018-06-29 21:56 ` Kees Cook
2018-07-01 6:29 ` Herbert Xu
2018-06-29 0:28 ` [PATCH v3 5/9] crypto: ahash: " Kees Cook
2018-06-29 0:28 ` [PATCH v3 6/9] dm verity fec: " Kees Cook
2018-06-29 0:28 ` [PATCH v3 7/9] crypto alg: Introduce generic max blocksize and alignmask Kees Cook
2018-06-29 0:28 ` [PATCH v3 8/9] crypto: qat: Remove VLA usage Kees Cook
2018-06-29 0:28 ` [PATCH v3 9/9] crypto: shash: Remove VLA usage in unaligned hashing Kees Cook
2018-06-30 7:03 ` Eric Biggers [this message]
2018-07-01 17:04 ` [dm-devel] " Kees Cook
2018-07-01 17:20 ` Eric Biggers
2018-07-02 17:34 ` Kees Cook
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180630070301.GA1706@sol.localdomain \
--to=ebiggers3@gmail.com \
--cc=agk@redhat.com \
--cc=arnd@arndb.de \
--cc=davem@davemloft.net \
--cc=dm-devel@redhat.com \
--cc=ebiggers@google.com \
--cc=giovanni.cabiddu@intel.com \
--cc=gustavo@embeddedor.com \
--cc=herbert@gondor.apana.org.au \
--cc=keescook@chromium.org \
--cc=larper@axis.com \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=qat-linux@intel.com \
--cc=rabinv@axis.com \
--cc=snitzer@redhat.com \
--cc=tim.c.chen@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).