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[libvirt] [PATCH 1/4] memory: make it safer to expand arrays



Note - I did _not_ update HACKING.  Do we have a makefile rule
for doing an auto-xsl translation from hacking.html.in yet, or
is something I'll have to do manually before pushing this?

* src/util/memory.h (VIR_REALLOC_N): Update docs.
(VIR_EXPAND_N, VIR_SHRINK_N): New macros.
(virAlloc, virAllocN, virReallocN, virAllocVar, virFree): Add some
gcc attributes.
* src/util/memory.c (virExpandN, virShrinkN): New functions.
(virReallocN): Update docs.
* docs/hacking.html.in: Prefer newer interfaces over
VIR_REALLOC_N, since uninitialized memory can bite us.
---
 docs/hacking.html.in |   24 +++++++++++--------
 src/util/memory.c    |   59 +++++++++++++++++++++++++++++++++++++++++++++++++-
 src/util/memory.h    |   51 ++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 117 insertions(+), 17 deletions(-)

diff --git a/docs/hacking.html.in b/docs/hacking.html.in
index deab530..4cc92f4 100644
--- a/docs/hacking.html.in
+++ b/docs/hacking.html.in
@@ -332,11 +332,11 @@
       Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
       codebase, because they encourage a number of serious coding bugs and do
       not enable compile time verification of checks for NULL. Instead of these
-      routines, use the macros from memory.h
+      routines, use the macros from memory.h.
     </p>

     <ul>
-      <li><p>eg to allocate  a single object:</p>
+      <li><p>To allocate a single object:</p>

 <pre>
       virDomainPtr domain;
@@ -347,11 +347,11 @@
       }
 </pre></li>

-      <li><p>eg to allocate an array of objects</p>
+      <li><p>To allocate an array of objects</p>

 <pre>
        virDomainPtr domains;
-       int ndomains = 10;
+       size_t ndomains = 10;

        if (VIR_ALLOC_N(domains, ndomains) &lt; 0) {
            virReportOOMError();
@@ -359,7 +359,7 @@
        }
 </pre></li>

-      <li><p>eg to allocate an array of object pointers</p>
+      <li><p>To allocate an array of object pointers</p>

 <pre>
        virDomainPtr *domains;
@@ -371,18 +371,22 @@
        }
 </pre></li>

-      <li><p>eg to re-allocate the array of domains to be longer</p>
+      <li><p>To re-allocate the array of domains to be 10 elements longer</p>

 <pre>
-       ndomains = 20
-
-       if (VIR_REALLOC_N(domains, ndomains) &lt; 0) {
+       if (VIR_EXPAND_N(domains, ndomains, 10) &lt; 0) {
            virReportOOMError();
            return NULL;
        }
 </pre></li>

-      <li><p>eg to free the domain</p>
+      <li><p>To trim an array of domains to have one less element</p>
+
+<pre>
+       VIR_SHRINK_N(domains, ndomains, 1);
+</pre></li>
+
+      <li><p>To free the domain</p>

 <pre>
        VIR_FREE(domain);
diff --git a/src/util/memory.c b/src/util/memory.c
index dd1216b..e95aa47 100644
--- a/src/util/memory.c
+++ b/src/util/memory.c
@@ -1,6 +1,7 @@
 /*
  * memory.c: safer memory allocation
  *
+ * Copyright (C) 2010 Red Hat, Inc.
  * Copyright (C) 2008 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -24,6 +25,7 @@
 #include <stddef.h>

 #include "memory.h"
+#include "ignore-value.h"


 #if TEST_OOM
@@ -141,7 +143,7 @@ int virAllocN(void *ptrptr, size_t size, size_t count)
  * 'count' elements, each 'size' bytes in length. Update 'ptrptr'
  * with the address of the newly allocated memory. On failure,
  * 'ptrptr' is not changed and still points to the original memory
- * block. The newly allocated memory is filled with zeros.
+ * block. Any newly allocated memory in 'ptrptr' is uninitialized.
  *
  * Returns -1 on failure to allocate, zero on success
  */
@@ -165,6 +167,61 @@ int virReallocN(void *ptrptr, size_t size, size_t count)
 }

 /**
+ * virExpandN:
+ * @ptrptr: pointer to pointer for address of allocated memory
+ * @size: number of bytes per element
+ * @countptr: pointer to number of elements in array
+ * @add: number of elements to add
+ *
+ * Resize the block of memory in 'ptrptr' to be an array of
+ * '*countptr' + 'add' elements, each 'size' bytes in length.
+ * Update 'ptrptr' and 'countptr'  with the details of the newly
+ * allocated memory. On failure, 'ptrptr' and 'countptr' are not
+ * changed. Any newly allocated memory in 'ptrptr' is zero-filled.
+ *
+ * Returns -1 on failure to allocate, zero on success
+ */
+int virExpandN(void *ptrptr, size_t size, size_t *countptr, size_t add)
+{
+    int res;
+
+    if (*countptr + add < *countptr) {
+        errno = ENOMEM;
+        return -1;
+    }
+    res = virReallocN(ptrptr, size, *countptr + add);
+    if (res == 0) {
+        memset(*(char **)ptrptr + (size * *countptr), 0, size * add);
+        *countptr += add;
+    }
+    return res;
+}
+
+/**
+ * virShrinkN:
+ * @ptrptr: pointer to pointer for address of allocated memory
+ * @size: number of bytes per element
+ * @countptr: pointer to number of elements in array
+ * @remove: number of elements to remove
+ *
+ * Resize the block of memory in 'ptrptr' to be an array of
+ * '*countptr' - 'remove' elements, each 'size' bytes in length.
+ * Update 'ptrptr' and 'countptr'  with the details of the newly
+ * allocated memory. If 'remove' is larger than 'countptr', free
+ * the entire array.
+ */
+void virShrinkN(void *ptrptr, size_t size, size_t *countptr, size_t remove)
+{
+    if (remove < *countptr)
+        ignore_value(virReallocN(ptrptr, size, *countptr -= remove));
+    else {
+        virFree(ptrptr);
+        *countptr = 0;
+    }
+}
+
+
+/**
  * Vir_Alloc_Var:
  * @ptrptr: pointer to hold address of allocated memory
  * @struct_size: size of initial struct
diff --git a/src/util/memory.h b/src/util/memory.h
index 60e2be6..98ac2b3 100644
--- a/src/util/memory.h
+++ b/src/util/memory.h
@@ -46,14 +46,21 @@


 /* Don't call these directly - use the macros below */
-int virAlloc(void *ptrptr, size_t size) ATTRIBUTE_RETURN_CHECK;
-int virAllocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK;
-int virReallocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK;
+int virAlloc(void *ptrptr, size_t size) ATTRIBUTE_RETURN_CHECK
+    ATTRIBUTE_NONNULL(1);
+int virAllocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK
+    ATTRIBUTE_NONNULL(1);
+int virReallocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK
+    ATTRIBUTE_NONNULL(1);
+int virExpandN(void *ptrptr, size_t size, size_t *count, size_t add)
+    ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
+void virShrinkN(void *ptrptr, size_t size, size_t *count, size_t remove)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
 int virAllocVar(void *ptrptr,
                 size_t struct_size,
                 size_t element_size,
-                size_t count) ATTRIBUTE_RETURN_CHECK;
-void virFree(void *ptrptr);
+                size_t count) ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1);
+void virFree(void *ptrptr) ATTRIBUTE_NONNULL(1);

 /**
  * VIR_ALLOC:
@@ -87,12 +94,44 @@ void virFree(void *ptrptr);
  *
  * Re-allocate an array of 'count' elements, each sizeof(*ptr)
  * bytes long and store the address of allocated memory in
- * 'ptr'. Fill the newly allocated memory with zeros
+ * 'ptr'. If 'ptr' grew, the added memory is uninitialized.
  *
  * Returns -1 on failure, 0 on success
  */
 # define VIR_REALLOC_N(ptr, count) virReallocN(&(ptr), sizeof(*(ptr)), (count))

+/**
+ * VIR_EXPAND_N:
+ * @ptr: pointer to hold address of allocated memory
+ * @count: variable tracking number of elements currently allocated
+ * @add: number of elements to add
+ *
+ * Re-allocate an array of 'count' elements, each sizeof(*ptr)
+ * bytes long, to be 'count' + 'add' elements long, then store the
+ * address of allocated memory in 'ptr' and the new size in 'count'.
+ * The new elements are filled with zero.
+ *
+ * Returns -1 on failure, 0 on success
+ */
+# define VIR_EXPAND_N(ptr, count, add) \
+    virExpandN(&(ptr), sizeof(*(ptr)), &(count), add)
+
+/**
+ * VIR_SHRINK_N:
+ * @ptr: pointer to hold address of allocated memory
+ * @count: variable tracking number of elements currently allocated
+ * @remove: number of elements to remove
+ *
+ * Re-allocate an array of 'count' elements, each sizeof(*ptr)
+ * bytes long, to be 'count' - 'remove' elements long, then store the
+ * address of allocated memory in 'ptr' and the new size in 'count'.
+ * If 'count' <= 'remove', the entire array is freed.
+ *
+ * No return value.
+ */
+# define VIR_SHRINK_N(ptr, count, remove) \
+    virShrinkN(&(ptr), sizeof(*(ptr)), &(count), remove)
+
 /*
  * VIR_ALLOC_VAR_OVERSIZED:
  * @M: size of base structure
-- 
1.7.2.1


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