Re: Undetected failures in getdomainname

[Matthew Fernandez <matthew.fernandez@nicta.com.au>]

On 23/06/16 02:31, Rich Felker wrote:
> On Wed, Jun 22, 2016 at 06:15:25PM +1000, Matthew Fernandez wrote:
>> Hi all,
>>
>> In the tip at time of writing
>> (6cec7bc57f599f43f4041cec2093e3c9231dbaab) there are a couple of
>> syscalls that are implemented by calling uname, notably gethostname
>> and getdomainname. In gethostname, the return value of uname is
>> checked and the code returns early if uname fails. However, in
>> getdomainname the return value of uname is ignored. I think it
>> should be following the same pattern as gethostname. Is this
>> correct?
>
> In practice I don't think the difference matters unless someone has
> hooked uname to fail (e.g. seccomp or perhaps LSMs), since the syscall
> itself can't fail. It wouldn't hurt to make them consistent though.

Good point. I hadn't factored in that the only uname failure case is when the buffer is invalid, which can never occur
when called from getdomainname.

>> Also, gethostname rolls its own strcpy, while getdomainname just
>> calls strcpy. However, maybe there is a good reason for this.
>
> As written the behaviors are different. gethostname truncates while
> getdomainname returns an error on excessive length. The former is
> mandated by POSIX; the latter is documented (but not clearly specified
> as a requirement vs just being an optional failure) in the Linux man
> page, since getdomainname is not a standard function.

Ah, nice. Learned something new today :) Thanks, Rich.

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