Changeset dd50aa19 in mainline

Timestamp:

2024-09-12T12:35:23Z (2 months ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master

Children:

899bdfd

Parents:

2ee6351

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-09-11 13:51:11)

git-committer:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-09-12 12:35:23)

Message:

Allocation function tweaks

• Add reallocarray() from POSIX 2024 for overflow-safe reallocations.
• Make realloc(x, 0) act as realloc(x, 1), and print an error message because it's unspecified behavior. Previous handling of realloc(x, 0) as free(x) is problematic, because proper realloc use will mistake it for failure if the case isn't specifically checked for, leading to double-free.
• Make malloc(0) act as malloc(1), since it "just works" when code forgets to specifically check for zero in cases where zero length is meaningful.

Files:

• common/include/stdlib.h (modified) (1 diff)
• kernel/generic/src/mm/malloc.c (modified) (1 diff)
• uspace/lib/c/generic/malloc.c (modified) (4 diffs)

common/include/stdlib.h

@@ -122 +122 @@
     __attribute__((malloc));
 
+extern void *reallocarray(void *ptr, size_t nelem, size_t elsize)
+    __attribute__((warn_unused_result));
+
 __HELENOS_DECLS_END;
 #endif

kernel/generic/src/mm/malloc.c

@@ -211 +211 @@
 void *realloc(void *old_obj, size_t new_size)
 {
+        if (new_size == 0)
+                new_size = 1;
+
         if (!old_obj)
                 return malloc(new_size);

uspace/lib/c/generic/malloc.c

@@ -38 +38 @@
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdio.h>
 #include <as.h>
 #include <align.h>
@@ -725 +726 @@
  *
  */
-static void *malloc_internal(const size_t size, const size_t align)
+static void *malloc_internal(size_t size, size_t align)
 {
         malloc_assert(first_heap_area != NULL);
 
+        if (size == 0)
+                size = 1;
+
         if (align == 0)
-                return NULL;
+                align = BASE_ALIGN;
 
         size_t falign = lcm(align, BASE_ALIGN);
@@ -821 +825 @@
  *
  */
-void *realloc(void *const addr, const size_t size)
+void *realloc(void *const addr, size_t size)
 {
         if (size == 0) {
-                free(addr);
-                return NULL;
+                fprintf(stderr, "realloc() called with size 0\n");
+                size = 1;
         }
 
@@ -930 +934 @@
 }
 
+/** Reallocate memory for an array
+ *
+ * Same as realloc(ptr, nelem * elsize), except the multiplication is checked
+ * for numerical overflow. Borrowed from POSIX 2024.
+ *
+ * @param ptr
+ * @param nelem
+ * @param elsize
+ *
+ * @return Reallocated memory or NULL.
+ */
+void *reallocarray(void *ptr, size_t nelem, size_t elsize)
+{
+        if (nelem > SIZE_MAX / elsize)
+                return NULL;
+
+        return realloc(ptr, nelem * elsize);
+}
+
 /** Free a memory block
  *