[libvirt] [PATCH v2 3/4] virDomainChrGetDomainPtrsInternal: Return an integer

[Peter Krempa]

On Thu, Jun 02, 2016 at 12:42:52 +0200, Michal Privoznik wrote:
> There's this problem on the recent gcc-6.1:
> 
> In file included from conf/domain_conf.c:37:0:
> conf/domain_conf.c: In function 'virDomainChrPreAlloc':
> conf/domain_conf.c:14109:35: error: potential null pointer dereference [-Werror=null-dereference]
>      return VIR_REALLOC_N(*arrPtr, *cntPtr + 1);
>                                    ^~
> ./util/viralloc.h:158:73: note: in definition of macro 'VIR_REALLOC_N'
>  # define VIR_REALLOC_N(ptr, count) virReallocN(&(ptr), sizeof(*(ptr)), (count), \
>                                                                          ^~~~~
> conf/domain_conf.c: In function 'virDomainChrRemove':
> conf/domain_conf.c:14133:21: error: potential null pointer dereference [-Werror=null-dereference]
>      for (i = 0; i < *cntPtr; i++) {
>                      ^~~~~~~
> 
> GCC basically fails to see, that the
> virDomainChrGetDomainPtrsInternal will never actually return NULL
> because it's never called over a domain char device with _LAST
> type. But to make it shut up, lets turn this function into
> returning an integer and check in the callers if a zero value
> value was returned.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/conf/domain_conf.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 568c699..2efe0a3 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -14038,7 +14038,7 @@ virDomainChrFind(virDomainDefPtr def,
>  
>  /* Return the address within vmdef to be modified when working with a
>   * chrdefptr of the given type.  */
> -static void
> +static int ATTRIBUTE_RETURN_CHECK
>  virDomainChrGetDomainPtrsInternal(virDomainDefPtr vmdef,
>                                    virDomainChrDeviceType type,
>                                    virDomainChrDefPtr ***arrPtr,
> @@ -14070,6 +14070,8 @@ virDomainChrGetDomainPtrsInternal(virDomainDefPtr vmdef,
>          *cntPtr = NULL;
>          break;
>      }
> +
> +    return (*arrPtr && *cntPtr) ? 0 : -1;

This doesn't set any error. The VIR_DOMAIN_CHR_DEVICE_TYPE_LAST case
should do so and possibly return -1 right away to avoid the ternary.

>  }
>  

[...]

> @@ -14104,7 +14105,9 @@ virDomainChrPreAlloc(virDomainDefPtr vmdef,
>      virDomainChrDefPtr **arrPtr = NULL;
>      size_t *cntPtr = NULL;
>  
> -    virDomainChrGetDomainPtrsInternal(vmdef, chr->deviceType, &arrPtr, &cntPtr);
> +    if (virDomainChrGetDomainPtrsInternal(vmdef, chr->deviceType,
> +                                          &arrPtr, &cntPtr) < 0)
> +        return -1;

So this will report the "unknown error".

>  
>      return VIR_REALLOC_N(*arrPtr, *cntPtr + 1);

ACK with the error added.