FreeBSD removed the HOST_NAME_MAX define in an attempt to have donwstream
consumers use the sysconf(3) API. This change has lead to various consumers
erroneously using the new API. Either mistaking _SC_HOST_NAME_MAX, which is
a parameter to sysconf(3) as the replacement of HOST_NAME_MAX or by using
sysconf(_SC_HOST_NAME_MAX) as a compile time constant which in turn can
lead to accidental introduction of variable length arrays (VLA).
The decision has been documented in /usr/include/sys/syslimits.h
/* * We leave the following values undefined to force applications to either * assume conservative values or call sysconf() to get the current value. * * HOST_NAME_MAX * * (We should do this for most of the values currently defined here, * but many programs are not prepared to deal with this yet.) */
The following snippet of code demonstrates _POSIX_HOST_NAME_MAX which is the
equivalent of HOST_NAME_MAX on most platforms and the confusion between _SC_HOST_NAME_MAX
and sysconf(_SC_HOST_NAME_MAX):
$ cat hostname.c #include <unistd.h> #include <stdio.h> #include <limits.h> int main(int argc, char **argv) { printf("_POSIX_HOST_NAME_MAX=%d\n", _POSIX_HOST_NAME_MAX); printf("_SC_HOST_NAME_MAX=%d\n", _SC_HOST_NAME_MAX); printf("sysconf(_SC_HOST_NAME_MAX)=%ld\n", sysconf(_SC_HOST_NAME_MAX)); return 0; }
Output:
$ ./hostname _POSIX_HOST_NAME_MAX=255 _SC_HOST_NAME_MAX=72 sysconf(_SC_HOST_NAME_MAX)=255 $
By accident _SC_HOST_NAME_MAX has a value large enough to not be spotted in most 'quick tests' people
might make.
This review addresses one of the places of misuse I found. Stay tuned as more will follow.
When committing any of these changes please credit the work as:
Sponsored by: Fudo Security
One of such consumers is port www/chromium where a patch was added:
files/patch-components_sync__device__info_local__device__info__util__linux.cc 7:- char hostname[HOST_NAME_MAX]; 8:- if (gethostname(hostname, HOST_NAME_MAX) == 0) // Success. 9:+ int len = sysconf(_SC_HOST_NAME_MAX); 11:+ if (gethostname(hostname, _SC_HOST_NAME_MAX) == 0) // Success.
The diff goes out of it's way to use sysconf(3) and introduces a variable length
array (VLA). It then fails to use the computed length in call to gethostname passing
in an accidental value '72'.
The proper non-intrusive fix for this codebase is to use _POSIX_HOST_NAME_MAX.
Interestingly, there was a different approach in another path in the same port:
files/patch-components_policy_core_common_cloud_cloud__policy__util.cc 35:+ char hostname[MAXHOSTNAMELEN]; 36:+ if (gethostname(hostname, MAXHOSTNAMELEN) == 0)
which uses MAXHOSTNAMELEN instead of HOST_NAME_MAX obtained indirectly (not present
in the patched file) by using sys/params.h in the source tree.
In the spirit of least intrusion into a fragile and important codebase like Chromium I'm
opting for the smallest change of using _POSIX_HOST_NAME_MAX instead of sysconf(3) and
not changing MAXHOSTNAMELEN as that is already a tested change.
Suggested commit message:
commit c17dc6b43ec3781fb2689e0d36c1c1c0b498aabc (HEAD -> main)
Author: Adam Wolk <a.wolk@fudosecurity.com>
Date: Fri Apr 30 21:04:16 2021 +0200
www/chromium: fix obtaining HOST_NAME_MAX
Using sysconf(3) API lead to accidental introduction of variable length arrays
(VLA) in the port. Additionally gethostname(3) has been passed _SC_HOST_NAME_MAX
incorrectly as the HOST_NAME_MAX length.
Fall back to using _POSIX_HOST_NAME_MAX as the remaining code is not ready for
introducing sysconf(3) as a patch.
Bump PORTREVISION to rebuild with the new patch.
Sponsored by: Fudo Security