On Tue, Nov 9, 2021 at 7:49 PM Richard W.M. Jones <[email protected]> wrote:
>
> ---
> common/include/Makefile.am | 1 +
> common/utils/Makefile.am | 3 +-
> common/include/checked-overflow.h | 61 +++++++++++++++++++++++++++++++
> common/utils/vector.c | 26 +++++++++----
> 4 files changed, 82 insertions(+), 9 deletions(-)
>
> diff --git a/common/include/Makefile.am b/common/include/Makefile.am
> index a7d0d026..52d97216 100644
> --- a/common/include/Makefile.am
> +++ b/common/include/Makefile.am
> @@ -37,6 +37,7 @@ EXTRA_DIST = \
> ascii-ctype.h \
> ascii-string.h \
> byte-swapping.h \
> + checked-overflow.h \
> exit-with-parent.h \
> isaligned.h \
> ispowerof2.h \
> diff --git a/common/utils/Makefile.am b/common/utils/Makefile.am
> index 55415535..012a5c25 100644
> --- a/common/utils/Makefile.am
> +++ b/common/utils/Makefile.am
> @@ -52,6 +52,7 @@ libutils_la_SOURCES = \
> $(NULL)
> libutils_la_CPPFLAGS = \
> -I$(top_srcdir)/include \
> + -I$(top_srcdir)/common/include \
> $(NULL)
> libutils_la_CFLAGS = \
> $(WARNINGS_CFLAGS) \
> @@ -101,7 +102,7 @@ test_quotes_CPPFLAGS = -I$(srcdir)
> test_quotes_CFLAGS = $(WARNINGS_CFLAGS)
>
> test_vector_SOURCES = test-vector.c vector.c vector.h bench.h
> -test_vector_CPPFLAGS = -I$(srcdir)
> +test_vector_CPPFLAGS = -I$(srcdir) -I$(top_srcdir)/common/include
> test_vector_CFLAGS = $(WARNINGS_CFLAGS)
>
> bench: test-vector
> diff --git a/common/include/checked-overflow.h
> b/common/include/checked-overflow.h
> new file mode 100644
> index 00000000..b571e2c6
> --- /dev/null
> +++ b/common/include/checked-overflow.h
> @@ -0,0 +1,61 @@
> +/* nbdkit
> + * Copyright (C) 2013-2021 Red Hat Inc.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions are
> + * met:
> + *
> + * * Redistributions of source code must retain the above copyright
> + * notice, this list of conditions and the following disclaimer.
> + *
> + * * Redistributions in binary form must reproduce the above copyright
> + * notice, this list of conditions and the following disclaimer in the
> + * documentation and/or other materials provided with the distribution.
> + *
> + * * Neither the name of Red Hat nor the names of its contributors may be
> + * used to endorse or promote products derived from this software without
> + * specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
> + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
> + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
> + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
> + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
> + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
> + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
> + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE.
> + */
> +
> +/* This header file defines functions for checking overflow in common
> + * integer arithmetic operations.
> + *
> + * It uses GCC/Clang built-ins: a possible future enhancement is to
> + * provide fallbacks in plain C or for other compilers. The only
> + * purpose of having a header file for this is to have a single place
> + * where we would extend this in future.
> + */
> +
> +#ifndef NBDKIT_CHECKED_OVERFLOW_H
> +#define NBDKIT_CHECKED_OVERFLOW_H
> +
> +#if !defined(__GNUC__) && !defined(__clang__)
> +#error "this file may need to be ported to your compiler"
> +#endif
> +
> +/* Add two uint64_t values. Returns true if overflow happened. */
> +#define ADD_UINT64_T_OVERFLOW(a, b, r) __builtin_add_overflow((a), (b), (r))
> +
> +/* Multiply two uint64_t values. Returns true if overflow happened. */
> +#define MUL_UINT64_T_OVERFLOW(a, b, r) __builtin_mul_overflow((a), (b), (r))
> +
> +/* Add two size_t values. Returns true if overflow happened. */
> +#define ADD_SIZE_T_OVERFLOW(a, b, r) __builtin_add_overflow((a), (b), (r))
> +
> +/* Multiple two size_t values. Returns true if overflow happened. */
> +#define MUL_SIZE_T_OVERFLOW(a, b, r) __builtin_mul_overflow((a), (b), (r))
> +
> +#endif /* NBDKIT_CHECKED_OVERFLOW_H */
> diff --git a/common/utils/vector.c b/common/utils/vector.c
> index dff051e9..e4ea7f3f 100644
> --- a/common/utils/vector.c
> +++ b/common/utils/vector.c
> @@ -36,6 +36,7 @@
> #include <stdlib.h>
> #include <errno.h>
>
> +#include "checked-overflow.h"
> #include "vector.h"
>
> int
> @@ -44,21 +45,30 @@ generic_vector_reserve (struct generic_vector *v, size_t
> n, size_t itemsize)
> void *newptr;
> size_t reqcap, reqbytes, newcap, newbytes;
>
> - /* New capacity requested. We must allocate this minimum (or fail). */
> - reqcap = v->cap + n;
> - reqbytes = reqcap * itemsize;
> - if (reqbytes < v->cap * itemsize) {
> + /* New capacity requested. We must allocate this minimum (or fail).
> + * reqcap = v->cap + n
> + * reqbytes = reqcap * itemsize
> + */
This should explain the next lines? I'm not sure about it, it makes
the code more complicated and the commented code can get out
of sync with the actual code.
> + if (ADD_SIZE_T_OVERFLOW (v->cap, n, &reqcap) ||
> + MUL_SIZE_T_OVERFLOW (reqcap, itemsize, &reqbytes)) {
Is order guaranteed?
I think it will be more clear as separate if blocks, even if we need
to have 2 blocks for returning ENOMEM.
> errno = ENOMEM;
> - return -1; /* overflow */
> + return -1;
> }
>
> /* However for the sake of optimization, scale buffer by 3/2 so that
> * repeated reservations don't call realloc often.
> + * newcap = v->cap + (v->cap + 1) / 2
> + * newbytes = newcap * itemsize
> */
> - newcap = v->cap + (v->cap + 1) / 2;
> - newbytes = newcap * itemsize;
> -
> + if (ADD_SIZE_T_OVERFLOW (v->cap, 1, &newcap))
> + goto fallback;
> + newcap /= 2;
> + if (ADD_SIZE_T_OVERFLOW (v->cap, newcap, &newcap))
> + goto fallback;
This probably works but adding v->cap and newcap and storing
back in newcap is pretty confusing. I would use a temporary:
if (ADD_SIZE_T_OVERFLOW (v->cap, 1, &extracap))
goto fallback;
extracap /= 2;
if (ADD_SIZE_T_OVERFLOW (v->cap, extracap, &newcap))
goto fallback;
> + if (MUL_SIZE_T_OVERFLOW (newcap, itemsize, &newbytes))
> + goto fallback;
> if (newbytes < reqbytes) {
> + fallback:
Jumping inside an if block is evil.
I would try to extract the code to compute the new capacity into a helper
function:
if (next_capacity(v-cap, n, itemsize, &newcap))
return -1;
This function can return early instead of jumping around or fail
if we cannot reserve n items. In the worst case this function will
only hide the overflow macros.
Nir
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