On Sun, May 05, 2019 at 06:49:30PM -0600, Jerry James wrote: > Awhile back, I mentioned that GCL was building in mock on my local > machine, but was segfaulting on the koji builders. By dint of much > experimentation, I now know what is going on. For the enlightenment > of anybody who cares: > > - GCL is linked with libtirpc. > - libtirpc is linked with libselinux. > - libselinux has a "constructor" function, init_lib(), that runs before > main(). > - init_lib() calls init_selinuxmnt() > - init_selinuxmnt() checks that /sys/fs/selinux exists, has type > SELINUX_MAGIC (see statfs(2)), and is not read-only. In mock on my > home machine, all of this is true, so execution stops there; the > library is initialized. > - On the koji builders, /sys/fs/selinux does exist, but is read-only, > so it fails the test. The code then does the same check on /selinux, > but that doesn't exist. Due to both failures, selinuxfs_exists() is > called to see if the running kernel even knows about selinuxfs. > - selinuxfs_exists() walks through the contents of /proc/filesystems. > That walk involves calls to getline(), which calls malloc(), and > free(). > - GCL has its own definitions of malloc() and free(), but those > definitions require that address randomization be turned off. GCL > accomplishes this with a call to personality() early in main(), but > the libselinux initializer runs before main(), resulting in GCL > segfaulting in free(). > > So the issue isn't really mock on my machine vs. koji: it is systems > where /sys/fs/selinux is mounted read-write versus those where it is > mounted read-only or not mounted at all. > > One workaround is to invoke GCL at build time with setarch -R gcl > <args>, but that means any GCL users who do not have /sys/fs/selinux > mounted read-write will have to do the same.
In the RPM build, move the real 'gcl' binary to /usr/libexec. Then create a /usr/bin/gcl that is just a shell script that invokes "setarch -R gcl /usr/libexec/gcl $@". Though as Florian suggests, the better solution is to not have the personality() call in main - have it called by malloc(), or possibly a constructor function that's part of the object providing the malloc replacement. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://getfedora.org/code-of-conduct.html List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org
