Re: [PATCH 1/2] avoid using inet_ntoa()

[Denis Kenzior <denkenz@gmail.com>]

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Hi Davide,

On 6/8/21 7:46 AM, d. caratti wrote:
> Il giorno lun 7 giu 2021 alle ore 20:41 Denis Kenzior
> <denkenz@gmail.com> ha scritto:
> 
>>
>> I would assume so.  You can tell for sure by looking at glibc implementation for
>> example.
>>
>> Oh, one other thing.  Have you checked the scope rules for GCC statement
>> expressions?  inet_ntoa uses a static buffer (which glibc further enhances by
>> marking it as thread-specific storage).  So the returned pointer is guaranteed
>> to be valid after inet_ntoa returns.  The statement expression doesn't seem to
>> do that, so that seems suspicious?
> 
> ... you are right. GCC documentation [1] says:
> 
> "In a statement expression, any temporaries created within a statement
> are destroyed at that statement’s end."
> 

That is what I was afraid of.

> so, we can't do IP_STR() that way. And using inet_ntop() + static
> buffer, like it's done by iproute2 [2] would actually
> silence the rpminspect warning I'm seeing, but not fix the actual
> problem: AFAIK use of a static buffer is one of the 2 reasons why
> inet_ntoa() has been "obsoleted".

That would be unfortunate.  I'm really not sure whether this needs to be 'fixed' 
anyway.  ell is meant for single-threaded, event driven apps.  So our use of 
inet_ntoa is just fine.  In fact we do similar stuff all over the place.

> 
> At this point, probably the cleanest thing to do is to replace
> IP_STR() with a proper call to inet_ntop(), preceded by declaration of
> buf[INET_ADDRSTRLEN] (like it's already done in some hunks of this
> patch). Luckily, it's just 10 places (versus 6 users of inet_ntoa(),
> still looks feasible).

Perhaps we can do something similar to MAC_STR instead?

> 
> Il giorno lun 7 giu 2021 alle ore 20:41 Denis Kenzior
> <denkenz@gmail.com> ha scritto:
>>
>>> that might be useful for other future CLIENT_DEBUG() users.
>>>
>>
>> Fair enough,  Wish there was a printf extension for ipv4 and ipv6 addresses like
>> printk uses...  Oh well.
> 
> yes, that would really make this game less boring :)
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
> [2] https://github.com/shemminger/iproute2/blob/main/lib/utils.c#L980-L1020
> 

Yep, that's the other thing we can do.  Just re-implement inet_ntoa or make our 
own version that covers v4/v6 with a static buffer.  Not sure that is any better 
than just using inet_ntoa though ;)

Regards,
-Denis