Re: [PATCH] pasta.c: modify hostname when detaching new namespace

[Danish Prakash <contact@danishpraka.sh>]

Hi Stefano,

I was caught up with some work last month, hence the delay in responses
since my last email.

On 5/24/24 11:09 PM, Stefano Brivio wrote:
>> +		if (sethostname(hostname, strlen(hostname)))
> 
> So, I mentioned before that you don't really need to set a NULL
> terminating byte for sethostname() itself, because it takes a length.
> 
> But strlen() needs it. If gethostname() truncated the hostname,
> according to POSIX, it's unspecified whether we'll have a NULL byte at
> the end of 'hostname', and strlen() would read out-of-bounds, past the
> end of 'hostname'.
> 
> That's not an issue with glibc, but if POSIX says it's not guaranteed,
> we shouldn't take anything for granted.
> 
> I would suggest that you simply add a NULL byte at HOST_NAME_MAX,
> unconditionally, that should cover the normal case as well as the
> ENAMETOOLONG case. I haven't tested this by the way.

Did you mean explicitly setting the NULL byte to `hostname`?

        hostname[HOST_NAME_MAX] = '\0';

Doing that after gethostname() and before sethostname() yields the
desired result. I tested a few cases, seems to be fine.

> 
>> +			warn("Unable to set pasta-prefixed hostname");
>> +	}
>> +
>>  	/* Wait for the parent to be ready: see main() */
>>  	sigemptyset(&set);
>>  	sigaddset(&set, SIGUSR1);
> 

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