kern/181127: [PATCH] set{domain, host}name doesn't permit NUL terminated strings that are MAXHOSTNAMELEN long

[Garrett Cooper]

On Aug 8, 2013, at 4:35 AM, Bruce Evans wrote:

> On Thu, 8 Aug 2013, Garrett Cooper wrote:
> 
>>> Synopsis:       [PATCH] set{domain,host}name doesn't permit NUL terminated strings that are MAXHOSTNAMELEN long
>> ...
>>> Description:
>> The noted link/patch fixes POSIX and generic requirement compliance for set{domain,host}name per the manpages by accounting for the fact that the string
>> must be NUL terminated.
> 
> The bugs seem to be mainly in the tests, so the proposed fix enlarges them.
> MAXHOSTNAMELEN is already 1 larger than the POSIX limit {HOST_NAME_MAX}
> (see the sysconf(3) sources).

So the fix is bogus. Ok, missed that MAXHOSTNAMELEN was '\0' inclusive.

>> Found with the NetBSD t_set{domain,host}name testcases:
>> 
>> Before:
>> 
>> $ pwd
>> /usr/tests/lib/libc/gen
>> $ sudo atf-run t_setdomainname | atf-report
>> t_setdomainname (1/1): 3 test cases
>>   setdomainname_basic: [0.019497s] Failed: /usr/src/lib/libc/tests/gen/t_setdomainname.c:66: setdomainname(domains[i],sizeof(domains[i])) == 0 not met
>>   setdomainname_limit: [0.004173s] Passed.
>>   setdomainname_perm: [0.005297s] Passed.
>> [0.029872s]
> 
> I'm not sure what these do, but according to the Synopsis,
> set{domain,host}name correctly doesn't permit NUL terminated strings that
> are MAXHOSTNAMELEN long (not counting space for the NUL).  MAXHOSTNAMELEN
> counts space for the NUL and is 1 larger than {HOST_NAME_MAX}.

Yes. It's kind of odd why NetBSD passes here, but this should work on FreeBSD as well as they aren't doing anything going out-of-bounds in the testcases (see https://github.com/yaneurabeya/freebsd/blob/master/lib/libc/tests/gen/t_setdomainname.c , https://github.com/yaneurabeya/freebsd/blob/master/lib/libc/tests/gen/t_sethostname.c if you're curious).

...

>> @@ -314,11 +314,11 @@ sysctl_hostname(SYSCTL_HANDLER_ARGS)
>> 
>> SYSCTL_PROC(_kern, KERN_HOSTNAME, hostname,
>>    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_MPSAFE,
>> -    (void *)(offsetof(struct prison, pr_hostname)), MAXHOSTNAMELEN,
>> +    (void *)(offsetof(struct prison, pr_hostname)), MAXHOSTNAMELEN+1,
>>    sysctl_hostname, "A", "Hostname");
>> SYSCTL_PROC(_kern, KERN_NISDOMAINNAME, domainname,
>>    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_MPSAFE,
>> -    (void *)(offsetof(struct prison, pr_domainname)), MAXHOSTNAMELEN,
>> +    (void *)(offsetof(struct prison, pr_domainname)), MAXHOSTNAMELEN+1,
>>    sysctl_hostname, "A", "Name of the current YP/NIS domain");
>> SYSCTL_PROC(_kern, KERN_HOSTUUID, hostuuid,
>>    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_MPSAFE,
> 
> The sysctls were originally simple SYSCTL_STRING()s and I think they
> worked then.  Now they are quite complicated, to  support jails, etc.,
> but they still use sysctl_handle_string() so I think they handle
> (non)strings and (non)termination the same.  Note that
> sysctl_handle_string() doesn't actually return strings unless the
> buffer is large enough to hold the NUL terminator.  It just truncates.
> This is reflected in the gethostname(3) API.  The name length for
> gethostname() must be 1 larger than {HOST_NAME_MAX} to ensure
> getting a string.  OTOH, the name length for sethostname(3) should
> not include space for the NUL, so it must not be larger than
> {HOST_NAME_MAX}.  If it is larger than {HOST_NAME_MAX}, then the
> syscall will just fail.  If it is larger than the string length
> (to include the NUL and possibly more) but not larger than
> {HOST_NAME_MAX}, then the syscall will succeed and the string will
> just be terminated more than once.  (It would be safer to write NULs
> from the end of the string until the end of the buffer in all cases.)

So translation is: is there's a bug in the sysctl handler after jail support was added and there's no reasonable way to fix it without reverting things back to their sane forms?

Thanks...