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=qpxydaacu1rq...@mail.gmail.com > > Signed-off-by: Kees Cook <keesc...@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-de...@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel
