Implement allocation buffers for internal use

This commit adds fixed-size allocation buffers.  The primary use
case is in NSS modules, where dynamically sized data is stored
in a fixed-size buffer provided by the caller.

Other uses include a replacement of mempcpy cascades (which is
safer due to the size checking inherent to allocation buffers).

1 files changed, 47 insertions, 0 deletions

diff --git a/malloc/alloc_buffer_alloc_array.c b/malloc/alloc_buffer_alloc_array.c
new file mode 100644
index 0000000000..68e14da8dd
--- /dev/null
+++ b/malloc/alloc_buffer_alloc_array.c
@@ -0,0 +1,47 @@
+/* Array allocation from a fixed-size buffer.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <alloc_buffer.h>
+#include <malloc-internal.h>
+#include <libc-pointer-arith.h>
+
+void *
+__libc_alloc_buffer_alloc_array (struct alloc_buffer *buf, size_t element_size,
+                                 size_t align, size_t count)
+{
+  size_t current = buf->__alloc_buffer_current;
+  /* The caller asserts that align is a power of two.  */
+  size_t aligned = ALIGN_UP (current, align);
+  size_t size;
+  bool overflow = check_mul_overflow_size_t (element_size, count, &size);
+  size_t new_current = aligned + size;
+  if (!overflow                /* Multiplication did not overflow.  */
+      && aligned >= current    /* No overflow in align step.  */
+      && new_current >= size   /* No overflow in size computation.  */
+      && new_current <= buf->__alloc_buffer_end) /* Room in buffer.  */
+    {
+      buf->__alloc_buffer_current = new_current;
+      return (void *) aligned;
+    }
+  else
+    {
+      alloc_buffer_mark_failed (buf);
+      return NULL;
+    }
+}
+libc_hidden_def (__libc_alloc_buffer_alloc_array)