Re: [Xen-devel] [PATCH 08/13 v3] libxl: don't leak ptr in libxl_list_vm error case

[Matthew Daley <mattd@xxxxxxxxxxx>]

On Mon, Dec 2, 2013 at 11:35 PM, Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/12/13 02:58, Matthew Daley wrote:
>> While at it, tidy up the function; there's no point in allocating more
>> than the amount of domains actually returned by xc_domain_getinfolist
>> (unless 0 domains are returned, in which case we should still allocate
>> one libxl_vminfo struct so we can return a non-NULL result and not
>> appear to have failed from the caller's perspective.)
>>
>> Coverity-ID: 1055888
>> Signed-off-by: Matthew Daley <mattd@xxxxxxxxxxx>
>> ---
>> v3: Oops, min() isn't defined or used anywhere in libxl. Just use a ternary
>> expression instead.
>>
>> v2: Always allocate at least one libxl_vminfo struct for the reason given in
>> the commit description.
>>
>>  tools/libxl/libxl.c |   14 +++++++-------
>>  1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
>> index b112294..1a2462c 100644
>> --- a/tools/libxl/libxl.c
>> +++ b/tools/libxl/libxl.c
>> @@ -674,17 +674,17 @@ libxl_vminfo * libxl_list_vm(libxl_ctx *ctx, int 
>> *nb_vm_out)
>>      libxl_vminfo *ptr;
>>      int idx, i, ret;
>>      xc_domaininfo_t info[1024];
>> -    int size = 1024;
>>
>> -    ptr = calloc(size, sizeof(libxl_vminfo));
>> -    if (!ptr)
>> +    ret = xc_domain_getinfolist(ctx->xch, 1, ARRAY_SIZE(info), info);
>> +    if (ret < 0) {
>> +        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "getting domain info list");
>>          return NULL;
>> +    }
>>
>> -    ret = xc_domain_getinfolist(ctx->xch, 1, 1024, info);
>> -    if (ret<0) {
>> -        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "geting domain info list");
>> +    ptr = calloc(ret ? ret : 1, sizeof(libxl_vminfo));
>
> Now I reconsider this, a comment in the code wouldn’t go amis, given the
> obscurity.

Agreed.

>
> Also, given -std=gnu99, you can use the gcc-ism of "ret ?: 1"

Eww, but OK.

- Matthew

>
>> +    if (!ptr)
>>          return NULL;
>> -    }
>> +
>>      for (idx = i = 0; i < ret; i++) {
>>          if (libxl_is_stubdom(ctx, info[i].domain, NULL))
>>              continue;
>

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