r13915: Fixed a very interesting class of realloc() bugs found by Coverity.

realloc can return NULL in one of two cases - (1) the realloc failed,
(2) realloc succeeded but the new size requested was zero, in which
case this is identical to a free() call.

The error paths dealing with these two cases should be different,
but mostly weren't. Secondly the standard idiom for dealing with
realloc when you know the new size is non-zero is the following :

 tmp = realloc(p, size);
 if (!tmp) {
    SAFE_FREE(p);
    return error;
 } else {
    p = tmp;
 }

However, there were *many* *many* places in Samba where we were
using the old (broken) idiom of :

 p = realloc(p, size)
 if (!p) {
    return error;
 }

which will leak the memory pointed to by p on realloc fail.

This commit (hopefully) fixes all these cases by moving to
a standard idiom of :

 p = SMB_REALLOC(p, size)
 if (!p) {
    return error;
 }

Where if the realloc returns null due to the realloc failing
or size == 0 we *guarentee* that the storage pointed to by p
has been freed. This allows me to remove a lot of code that
was dealing with the standard (more verbose) method that required
a tmp pointer. This is almost always what you want. When a
realloc fails you never usually want the old memory, you
want to free it and get into your error processing asap.

For the 11 remaining cases where we really do need to keep the
old pointer I have invented the new macro SMB_REALLOC_KEEP_OLD_ON_ERROR,
which can be used as follows :

 tmp = SMB_REALLOC_KEEP_OLD_ON_ERROR(p, size);
 if (!tmp) {
    SAFE_FREE(p);
    return error;
 } else {
    p = tmp;
 }

SMB_REALLOC_KEEP_OLD_ON_ERROR guarentees never to free the
pointer p, even on size == 0 or realloc fail. All this is
done by a hidden extra argument to Realloc(), BOOL free_old_on_error
which is set appropriately by the SMB_REALLOC and SMB_REALLOC_KEEP_OLD_ON_ERROR
macros (and their array counterparts).

It remains to be seen what this will do to our Coverity bug count :-).

Jeremy.
(This used to be commit 1d710d06a214f3f1740e80e0bffd6aab44aac2b0)

1 files changed, 71 insertions, 28 deletions

diff --git a/source3/lib/util.c b/source3/lib/util.c
index d4443a6480..758ebfd27d 100644
--- a/source3/lib/util.c
+++ b/source3/lib/util.c
@@ -291,13 +291,15 @@ void add_gid_to_array_unique(TALLOC_CTX *mem_ctx, gid_t gid,
 			return;
 	}
 
-	if (mem_ctx != NULL)
+	if (mem_ctx != NULL) {
 		*gids = TALLOC_REALLOC_ARRAY(mem_ctx, *gids, gid_t, *num_gids+1);
-	else
+	} else {
 		*gids = SMB_REALLOC_ARRAY(*gids, gid_t, *num_gids+1);
+	}
 
-	if (*gids == NULL)
+	if (*gids == NULL) {
 		return;
+	}
 
 	(*gids)[*num_gids] = gid;
 	*num_gids += 1;
@@ -342,14 +344,10 @@ const char *get_numlist(const char *p, uint32 **num, int *count)
 	(*num  ) = NULL;
 
 	while ((p = Atoic(p, &val, ":,")) != NULL && (*p) != ':') {
-		uint32 *tn;
-		
-		tn = SMB_REALLOC_ARRAY((*num), uint32, (*count)+1);
-		if (tn == NULL) {
-			SAFE_FREE(*num);
+		*num = SMB_REALLOC_ARRAY((*num), uint32, (*count)+1);
+		if (!(*num)) {
 			return NULL;
-		} else
-			(*num) = tn;
+		}
 		(*num)[(*count)] = val;
 		(*count)++;
 		p++;
@@ -941,32 +939,68 @@ void *calloc_array(size_t size, size_t nmemb)
 
 /****************************************************************************
  Expand a pointer to be a particular size.
+ Note that this version of Realloc has an extra parameter that decides
+ whether to free the passed in storage on allocation failure or if the
+ new size is zero.
+
+ This is designed for use in the typical idiom of :
+
+ p = SMB_REALLOC(p, size)
+ if (!p) {
+    return error;
+ }
+
+ and not to have to keep track of the old 'p' contents to free later, nor
+ to worry if the size parameter was zero. In the case where NULL is returned
+ we guarentee that p has been freed.
+
+ If free later semantics are desired, then pass 'free_old_on_error' as False which
+ guarentees that the old contents are not freed on error, even if size == 0. To use
+ this idiom use :
+
+ tmp = SMB_REALLOC_KEEP_OLD_ON_ERROR(p, size);
+ if (!tmp) {
+    SAFE_FREE(p);
+    return error;
+ } else {
+    p = tmp;
+ }
+
+ Changes were instigated by Coverity error checking. JRA.
 ****************************************************************************/
 
-void *Realloc(void *p,size_t size)
+void *Realloc(void *p, size_t size, BOOL free_old_on_error)
 {
 	void *ret=NULL;
 
 	if (size == 0) {
-		SAFE_FREE(p);
-		DEBUG(5,("Realloc asked for 0 bytes\n"));
+		if (free_old_on_error) {
+			SAFE_FREE(p);
+		}
+		DEBUG(2,("Realloc asked for 0 bytes\n"));
 		return NULL;
 	}
 
 #if defined(PARANOID_MALLOC_CHECKER)
-	if (!p)
+	if (!p) {
 		ret = (void *)malloc_(size);
-	else
+	} else {
 		ret = (void *)realloc_(p,size);
+	}
 #else
-	if (!p)
+	if (!p) {
 		ret = (void *)malloc(size);
-	else
+	} else {
 		ret = (void *)realloc(p,size);
+	}
 #endif
 
-	if (!ret)
+	if (!ret) {
+		if (free_old_on_error && p) {
+			SAFE_FREE(p);
+		}
 		DEBUG(0,("Memory allocation error: failed to expand to %d bytes\n",(int)size));
+	}
 
 	return(ret);
 }
@@ -975,23 +1009,28 @@ void *Realloc(void *p,size_t size)
  Type-safe realloc.
 ****************************************************************************/
 
-void *realloc_array(void *p,size_t el_size, unsigned int count)
+void *realloc_array(void *p, size_t el_size, unsigned int count, BOOL keep_old_on_error)
 {
 	if (count >= MAX_ALLOC_SIZE/el_size) {
+		if (!keep_old_on_error) {
+			SAFE_FREE(p);
+		}
 		return NULL;
 	}
-	return Realloc(p,el_size*count);
+	return Realloc(p, el_size*count, keep_old_on_error);
 }
 
 /****************************************************************************
- (Hopefully) efficient array append
+ (Hopefully) efficient array append.
 ****************************************************************************/
+
 void add_to_large_array(TALLOC_CTX *mem_ctx, size_t element_size,
 			void *element, void **array, uint32 *num_elements,
 			ssize_t *array_size)
 {
-	if (*array_size < 0)
+	if (*array_size < 0) {
 		return;
+	}
 
 	if (*array == NULL) {
 		if (*array_size == 0) {
@@ -1002,13 +1041,15 @@ void add_to_large_array(TALLOC_CTX *mem_ctx, size_t element_size,
 			goto error;
 		}
 
-		if (mem_ctx != NULL)
+		if (mem_ctx != NULL) {
 			*array = TALLOC(mem_ctx, element_size * (*array_size));
-		else
+		} else {
 			*array = SMB_MALLOC(element_size * (*array_size));
+		}
 
-		if (*array == NULL)
+		if (*array == NULL) {
 			goto error;
+		}
 	}
 
 	if (*num_elements == *array_size) {
@@ -1018,15 +1059,17 @@ void add_to_large_array(TALLOC_CTX *mem_ctx, size_t element_size,
 			goto error;
 		}
 
-		if (mem_ctx != NULL)
+		if (mem_ctx != NULL) {
 			*array = TALLOC_REALLOC(mem_ctx, *array,
 						element_size * (*array_size));
-		else
+		} else {
 			*array = SMB_REALLOC(*array,
 					     element_size * (*array_size));
+		}
 
-		if (*array == NULL)
+		if (*array == NULL) {
 			goto error;
+		}
 	}
 
 	memcpy((char *)(*array) + element_size*(*num_elements),