Mailing List Archive: [PATCH] libxl: correct allocation size in libxl_list

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1310734995 -3600
# Node ID 89074871f15c01c9c6447d8e1814f0b6d0abe592
# Parent ebbd0497524ac8ef7c03864d95a91c4a9ecf2280
libxl: correct allocation size in libxl_list_vm

*ptr has type libxl_vminfo not libxl_domid, so correct calloc call.

This the second instance of this bug I've noticed recently, I did a
quick audit of other similar uses of sizeof(...) and all I spotted
were a couple of harmlessly reversed calloc arguments. It's a pretty
strong argument for "foo = ..alloc(sizeof(*foo))" rather than
"alloc(sizeof(foos_type))" though...

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r ebbd0497524a -r 89074871f15c tools/libxl/libxl.c
--- a/tools/libxl/libxl.c Fri Jul 15 13:29:53 2011 +0100
+++ b/tools/libxl/libxl.c Fri Jul 15 14:03:15 2011 +0100
@@ -449,7 +449,7 @@ libxl_vminfo * libxl_list_vm(libxl_ctx *
xc_domaininfo_t info[1024];
int size = 1024;

- ptr = calloc(size, sizeof(libxl_dominfo));
+ ptr = calloc(size, sizeof(libxl_vminfo));
if (!ptr)
return NULL;

diff -r ebbd0497524a -r 89074871f15c tools/libxl/libxl_dm.c
--- a/tools/libxl/libxl_dm.c Fri Jul 15 13:29:53 2011 +0100
+++ b/tools/libxl/libxl_dm.c Fri Jul 15 14:03:15 2011 +0100
@@ -757,7 +757,7 @@ retry_transaction:
libxl_domain_unpause(ctx, domid);

if (starting_r) {
- *starting_r = calloc(sizeof(libxl__device_model_starting), 1);
+ *starting_r = calloc(1, sizeof(libxl__device_model_starting));
(*starting_r)->domid = info->domid;
(*starting_r)->dom_path = libxl__xs_get_dompath(gc, info->domid);
(*starting_r)->for_spawn = NULL;
@@ -834,11 +834,11 @@ int libxl__create_device_model(libxl__gc

if (starting_r) {
rc = ERROR_NOMEM;
- *starting_r = calloc(sizeof(libxl__device_model_starting), 1);
+ *starting_r = calloc(1, sizeof(libxl__device_model_starting));
if (!*starting_r)
goto out_close;
p = *starting_r;
- p->for_spawn = calloc(sizeof(libxl__spawn_starting), 1);
+ p->for_spawn = calloc(1, sizeof(libxl__spawn_starting));
} else {
p = &buf_starting;
p->for_spawn = NULL;

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Ian Campbell writes ("[Xen-devel] [PATCH] libxl: correct allocation size in libxl_list_vm"):
> libxl: correct allocation size in libxl_list_vm

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

> *ptr has type libxl_vminfo not libxl_domid, so correct calloc call.
>
> This the second instance of this bug I've noticed recently, I did a
> quick audit of other similar uses of sizeof(...) and all I spotted
> were a couple of harmlessly reversed calloc arguments. It's a pretty
> strong argument for "foo = ..alloc(sizeof(*foo))" rather than
> "alloc(sizeof(foos_type))" though...

The correct approach to this is to make a macro along these lines:

#define OUR_CALLOC(foo) ((foo)=calloc(sizeof(*(foo))))

I think we may have some of these but we should have a complete set.

Ian.

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