Re: [Xen-devel] [PATCH] tools: Fix wild memory allocations from c/s 250f0b4 and 85d78b4

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 05/18/2015 08:57 AM, Andrew Cooper wrote:
> These changesets cause the respective libxc functions to unconditonally
> dereference their max_cpus/nodes parameters as part of initial memory
> allocations.  It will fail at obtaining the correct number of cpus/nodes from
> Xen, as the guest handles will not be NULL.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>
> ---
> Spotted by XenServers Coverity run.
> ---
>   tools/libxl/libxl.c               |    4 ++--
>   tools/misc/xenpm.c                |    4 ++--
>   tools/python/xen/lowlevel/xc/xc.c |    4 ++--
>   3 files changed, 6 insertions(+), 6 deletions(-)
xenpm bug is already fixed (commit 
b315cd9cce5b6da7ca89b2d7bad3fb01e7716044 n the staging tree).
I am not sure I understand why Coverity complains about other spots. For 
example, in libxl_get_cpu_topology() num_cpus can be left uninitialized 
only if xc_cputopoinfo(ctx->xch, &num_cpus, NULL) fails, in which case 
we go to 'GC_FREE;  return ret;', so it's not ever used.

-boris


> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index a6eb2df..295877b 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -5105,7 +5105,7 @@ libxl_cputopology *libxl_get_cpu_topology(libxl_ctx *ctx, 
> int *nb_cpu_out)
>       xc_cputopo_t *cputopo;
>       libxl_cputopology *ret = NULL;
>       int i;
> -    unsigned num_cpus;
> +    unsigned num_cpus = 0;
>   
>       /* Setting buffer to NULL makes the call return number of CPUs */
>       if (xc_cputopoinfo(ctx->xch, &num_cpus, NULL))
> @@ -5191,7 +5191,7 @@ libxl_numainfo *libxl_get_numainfo(libxl_ctx *ctx, int 
> *nr)
>       uint32_t *distance;
>       libxl_numainfo *ret = NULL;
>       int i, j;
> -    unsigned num_nodes;
> +    unsigned num_nodes = 0;
>   
>       if (xc_numainfo(ctx->xch, &num_nodes, NULL, NULL)) {
>           LOGE(ERROR, "Unable to determine number of nodes");
> diff --git a/tools/misc/xenpm.c b/tools/misc/xenpm.c
> index fe2c001..2f9bd8e 100644
> --- a/tools/misc/xenpm.c
> +++ b/tools/misc/xenpm.c
> @@ -356,7 +356,7 @@ static void signal_int_handler(int signo)
>       struct timeval tv;
>       int cx_cap = 0, px_cap = 0;
>       xc_cputopo_t *cputopo = NULL;
> -    unsigned max_cpus;
> +    unsigned max_cpus = 0;
>   
>       if ( xc_cputopoinfo(xc_handle, &max_cpus, NULL) != 0 )
>       {
> @@ -961,7 +961,7 @@ void scaling_governor_func(int argc, char *argv[])
>   void cpu_topology_func(int argc, char *argv[])
>   {
>       xc_cputopo_t *cputopo = NULL;
> -    unsigned max_cpus;
> +    unsigned max_cpus = 0;
>       int i, rc;
>   
>       if ( xc_cputopoinfo(xc_handle, &max_cpus, NULL) != 0 )
> diff --git a/tools/python/xen/lowlevel/xc/xc.c 
> b/tools/python/xen/lowlevel/xc/xc.c
> index fbd93db..c77e15b 100644
> --- a/tools/python/xen/lowlevel/xc/xc.c
> +++ b/tools/python/xen/lowlevel/xc/xc.c
> @@ -1221,7 +1221,7 @@ static PyObject *pyxc_getcpuinfo(XcObject *self, PyObject 
> *args, PyObject *kwds)
>   static PyObject *pyxc_topologyinfo(XcObject *self)
>   {
>       xc_cputopo_t *cputopo = NULL;
> -    unsigned i, num_cpus;
> +    unsigned i, num_cpus = 0;
>       PyObject *ret_obj = NULL;
>       PyObject *cpu_to_core_obj, *cpu_to_socket_obj, *cpu_to_node_obj;
>   
> @@ -1293,7 +1293,7 @@ static PyObject *pyxc_topologyinfo(XcObject *self)
>   
>   static PyObject *pyxc_numainfo(XcObject *self)
>   {
> -    unsigned i, j, num_nodes;
> +    unsigned i, j, num_nodes = 0;
>       uint64_t free_heap;
>       PyObject *ret_obj = NULL, *node_to_node_dist_list_obj;
>       PyObject *node_to_memsize_obj, *node_to_memfree_obj;

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