| Message ID | 20180620190408.45104-8-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | Mike Snitzer |
| Headers | show |
On Wed, Jun 20, 2018 at 12:04:04PM -0700, Kees Cook wrote: > In the quest to remove all stack VLA usage from the kernel[1], this uses > the maximum blocksize and adds a sanity check. > > [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > crypto/xcbc.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/crypto/xcbc.c b/crypto/xcbc.c > index 25c75af50d3f..016481b1f3ba 100644 > --- a/crypto/xcbc.c > +++ b/crypto/xcbc.c > @@ -65,7 +65,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent, > int bs = crypto_shash_blocksize(parent); > u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1); > int err = 0; > - u8 key1[bs]; > + u8 key1[CRYPTO_ALG_MAX_BLOCKSIZE]; > + > + if (WARN_ON(bs > sizeof(key1))) > + return -EINVAL; Similarly, why not MAX_CIPHER_BLOCKSIZE? Also, xcbc_create() only allows a 16-byte block size, and you made the API enforce the maximum for algorithms anyway. So I think the extra check here isn't very worthwhile. - Eric -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
On Wed, Jun 20, 2018 at 4:46 PM, Eric Biggers <ebiggers3@gmail.com> wrote: > On Wed, Jun 20, 2018 at 12:04:04PM -0700, Kees Cook wrote: >> In the quest to remove all stack VLA usage from the kernel[1], this uses >> the maximum blocksize and adds a sanity check. >> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com >> >> Signed-off-by: Kees Cook <keescook@chromium.org> >> --- >> crypto/xcbc.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/crypto/xcbc.c b/crypto/xcbc.c >> index 25c75af50d3f..016481b1f3ba 100644 >> --- a/crypto/xcbc.c >> +++ b/crypto/xcbc.c >> @@ -65,7 +65,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent, >> int bs = crypto_shash_blocksize(parent); >> u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1); >> int err = 0; >> - u8 key1[bs]; >> + u8 key1[CRYPTO_ALG_MAX_BLOCKSIZE]; >> + >> + if (WARN_ON(bs > sizeof(key1))) >> + return -EINVAL; > > Similarly, why not MAX_CIPHER_BLOCKSIZE? > > Also, xcbc_create() only allows a 16-byte block size, and you made the API > enforce the maximum for algorithms anyway. So I think the extra check here > isn't very worthwhile. Is the "parent" argument in crypto_xcbc_digest_setkey() always going to be the "alg" from xcbc_create()? I couldn't convince myself that was true. If it is, then yes, this VLA can trivially made to be 16, but it seemed like they were separate instances... -Kees
On Wed, Jun 20, 2018 at 05:10:04PM -0700, Kees Cook wrote: > On Wed, Jun 20, 2018 at 4:46 PM, Eric Biggers <ebiggers3@gmail.com> wrote: > > On Wed, Jun 20, 2018 at 12:04:04PM -0700, Kees Cook wrote: > >> In the quest to remove all stack VLA usage from the kernel[1], this uses > >> the maximum blocksize and adds a sanity check. > >> > >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com > >> > >> Signed-off-by: Kees Cook <keescook@chromium.org> > >> --- > >> crypto/xcbc.c | 5 ++++- > >> 1 file changed, 4 insertions(+), 1 deletion(-) > >> > >> diff --git a/crypto/xcbc.c b/crypto/xcbc.c > >> index 25c75af50d3f..016481b1f3ba 100644 > >> --- a/crypto/xcbc.c > >> +++ b/crypto/xcbc.c > >> @@ -65,7 +65,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent, > >> int bs = crypto_shash_blocksize(parent); > >> u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1); > >> int err = 0; > >> - u8 key1[bs]; > >> + u8 key1[CRYPTO_ALG_MAX_BLOCKSIZE]; > >> + > >> + if (WARN_ON(bs > sizeof(key1))) > >> + return -EINVAL; > > > > Similarly, why not MAX_CIPHER_BLOCKSIZE? > > > > Also, xcbc_create() only allows a 16-byte block size, and you made the API > > enforce the maximum for algorithms anyway. So I think the extra check here > > isn't very worthwhile. > > Is the "parent" argument in crypto_xcbc_digest_setkey() always going > to be the "alg" from xcbc_create()? I couldn't convince myself that > was true. If it is, then yes, this VLA can trivially made to be 16, > but it seemed like they were separate instances... Yes, it's guaranteed to be an instance of "xcbc" which was created by xcbc_create(), so it will have 'cra_blocksize == 16'. So until someone actually tests and enables support in the "xcbc" template for other block sizes (if the XCBC specification allows them), it would also be fine to just '#define XCBC_BLOCK_SIZE 16' at the top of the file and use that everywhere that references the block size. Eric -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
diff --git a/crypto/xcbc.c b/crypto/xcbc.c index 25c75af50d3f..016481b1f3ba 100644 --- a/crypto/xcbc.c +++ b/crypto/xcbc.c @@ -65,7 +65,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent, int bs = crypto_shash_blocksize(parent); u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1); int err = 0; - u8 key1[bs]; + u8 key1[CRYPTO_ALG_MAX_BLOCKSIZE]; + + if (WARN_ON(bs > sizeof(key1))) + return -EINVAL; if ((err = crypto_cipher_setkey(ctx->child, inkey, keylen))) return err;
In the quest to remove all stack VLA usage from the kernel[1], this uses the maximum blocksize and adds a sanity check. [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com Signed-off-by: Kees Cook <keescook@chromium.org> --- crypto/xcbc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)