[SSSD] [PATCHES] struct sockaddr casting
Michal Židek
mzidek at redhat.com
Tue Oct 1 17:04:19 UTC 2013
On 10/01/2013 06:59 PM, Michal Židek wrote:
> Hello,
>
> these are the patches, that solve the casting of sockaddr structure.
>
> Patch 0001 - Adds function to filter out special ip addresses (loopback,
> multicast, linklocal, broadcast) and also a unit test for it. Used in
> later patches.
>
> Patch 0002 and 0003 - Use the function from patch 0001 and properly copy
> the sockaddr_in structure to avoid alignment warnings.
>
> Patch 0004 - Avoid casting of sockaddr to sockaddr_in in tests.
>
>
> Also here is the discussion from diffrent thread, related to sockaddr
> casting:
>
> // PASTE BEGIN
>
> >>>>> I tested some compilers and patches work fine with clang and gcc.
> >>>>> But there are also another compilers in the world
> >>>>> ant they needn't understand "pragma GCC". This pragma is not
> standardized.
> >>>>>
> >>>>>
> >>>>> src/providers/dp_dyndns.c(145): warning #161: unrecognized #pragma
> >>>>> #pragma GCC diagnostic push
> >>>>> ^
> >>>>>
> >>>>> src/providers/dp_dyndns.c(146): warning #161: unrecognized #pragma
> >>>>> #pragma GCC diagnostic ignored "-Wcast-align"
> >>>>> ^
> >>>>>
> >>>>> src/providers/dp_dyndns.c(206): warning #161: unrecognized #pragma
> >>>>> #pragma GCC diagnostic pop
> >>>>> ^
> >>>>>
> >>>>> If you are 100% sure about alignment, you can define own macro.
> >>>>>
> >>>>> Something like this:
> >>>>> #define ignore_align(var, dest_type) \
> >>>>> (dest_type *)((void*)(var))
> >>>>>
> >>>>> And usage:
> >>>>> wrapper->refcount = ignore_align(wrapper->ptr +
> refcount_offset, int);
> >>>>>
> >>>>>
> >>>>> Does anybody have any better ideas?
> >>>> Compiler specific #pragma should not be used. And I think in general
> >>>> #pragma should be used with great care. Currently there is only
> one use
> >>>> case in sssd in the memcache code to align some structs which make
> >>>> sense.
> >>> Indeed, agree 100%
> >>>
> >>>> Especially I think ingnoring a warning is not a good idea. If
> currently
> >>>> no one has a good idea how to handle the sockaddr and in_addr
> structs in
> >>>> a way which does not produce a warning I would prefer to keep the
> >>>> warning around until someone has a good idea. Imo a comment in the
> code
> >>>> that the warning can be ignored would be sufficient for the time
> being.
> >>> casting sockaddr is a bug, unless you know for sure it was created as
> >>> sockaddr_un and then simply casted to sockaddr, but in that case I
> would
> >>> consider the casting to pass it around just a different bug.
> >>>
> >>> Please use sockaddr_un anywhere you need to perform casts. Pass around
> >>> sockaddr_un and cast it only at the time of use when needed.
> >> It is not possible to use sockaddr_un(or sockaddr_storage).
> >>
> >> We use function getifaddrs to retrieve addresses of network interfaces.
> >>
> >> Manual page says (man 3 getifaddrs)
> >>
> --------------------------------------------------------------------------
> >> int getifaddrs(struct ifaddrs **ifap);
> >>
> >> The getifaddrs() function creates a linked list of
> structures
> >> describing the network interfaces of the local system, and
> stores
> >> the address of the first item of the list in *ifap.
> >> The list consists of ifaddrs structures, defined as follows:
> >>
> >> struct ifaddrs {
> >> struct ifaddrs *ifa_next; /* Next item in list */
> >> char *ifa_name; /* Name of interface */
> >> unsigned int ifa_flags; /* Flags from
> SIOCGIFFLAGS */
> >> struct sockaddr *ifa_addr; /* Address of
> interface */
> >> ^^^^^^^^^^^^^^^
> >> We cannot change this type
> >> struct sockaddr *ifa_netmask; /* Netmask of
> interface */
> >> union {
> >> struct sockaddr *ifu_broadaddr;
> >> /* Broadcast address of
> interface */
> >> struct sockaddr *ifu_dstaddr;
> >> /* Point-to-point destination
> address */
> >> } ifa_ifu;
> >> #define ifa_broadaddr ifa_ifu.ifu_broadaddr
> >> #define ifa_dstaddr ifa_ifu.ifu_dstaddr
> >> void *ifa_data; /* Address-specific
> data */
> >> };
> >>
> >>
> --------------------------------------------------------------------------
> > In this case you should copy the contents of sockaddr to a new variable
> > of the right type, and not cast.
> >
> > Simo.
> >
> Yes, this is the only way you can deal with these issues.
> I remembered this from my experiments with ELAPI 3 years ago.
> I ran into similar problems with this function and had to copy data.
>
And now with patches.
Michal
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