c8ba7968b3
libselinux implements a cache mechanism for get*con() functions, such
that when a thread calls setcon(...) then getcon(...), the context is
directly returned. Unfortunately, getpidcon(pid, &context) uses the same
cached variable, so when a program uses setcon("something"), all later
calls to getpidcon(pid, ...) returns "something". This is a bug.
Here is a program which illustrates this bug:
#include <stdio.h>
#include <selinux/selinux.h>
int main() {
char *context = "";
if (getpidcon(1, &context) < 0) {
perror("getpidcon(1)");
}
printf("getpidcon(1) = %s\n", context);
if (getcon(&context) < 0) {
perror("getcon()");
}
printf("getcon() = %s\n", context);
if (setcon(context) < 0) {
perror("setcon()");
}
if (getpidcon(1, &context) < 0) {
perror("getpidcon(1)");
}
printf("getpidcon(1) = %s\n", context);
return 0;
}
On an Arch Linux system using unconfined user, this program displays:
getpidcon(1) = system_u:system_r:init_t
getcon() = unconfined_u:unconfined_r:unconfined_t
getpidcon(1) = unconfined_u:unconfined_r:unconfined_t
With this commit, this program displays:
getpidcon(1) = system_u:system_r:init_t
getcon() = unconfined_u:unconfined_r:unconfined_t
getpidcon(1) = system_u:system_r:init_t
This bug was present in the first commit of
https://github.com/SELinuxProject/selinux git history. It was reported
in https://lore.kernel.org/selinux/20220121084012.GS7643@suse.com/ and a
patch to fix it was sent in
https://patchwork.kernel.org/project/selinux/patch/20220127130741.31940-1-jsegitz@suse.de/
without a clear explanation. This patch added pid checks, which made
sense but were difficult to read. Instead, it is possible to change the
way the functions are called so that they directly know which cache
variable to use.
Moreover, as the code is not clear at all (I spent too much time trying
to understand what the switch did and what the thread-local variable
contained), this commit also reworks libselinux/src/procattr.c to:
- not use hard-to-understand switch/case constructions on strings (they
are replaced by a new argument filled by macros)
- remove getpidattr_def macro (it was only used once, for pidcon, and
the code is clearer with one less macro)
- remove the pid parameter of setprocattrcon() and setprocattrcon_raw()
(it is always zero)
Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
Cc: Johannes Segitz <jsegitz@suse.de>
|
||
|---|---|---|
| .circleci | ||
| .github/workflows | ||
| checkpolicy | ||
| dbus | ||
| gui | ||
| libselinux | ||
| libsemanage | ||
| libsepol | ||
| mcstrans | ||
| policycoreutils | ||
| python | ||
| restorecond | ||
| sandbox | ||
| scripts | ||
| secilc | ||
| semodule-utils | ||
| .gitignore | ||
| .travis.yml | ||
| CleanSpec.mk | ||
| CONTRIBUTING.md | ||
| lgtm.yml | ||
| Makefile | ||
| README.md | ||
| SECURITY.md | ||
| VERSION | ||
SELinux Userspace
Please submit all bug reports and patches to selinux@vger.kernel.org.
Subscribe by sending "subscribe selinux" in the body of an email to majordomo@vger.kernel.org.
Archive of this mailing list is available on https://lore.kernel.org/selinux/.
Installation
SELinux libraries and tools are packaged in several Linux distributions:
- Alpine Linux (https://pkgs.alpinelinux.org/package/edge/testing/x86/policycoreutils)
- Arch Linux User Repository (https://aur.archlinux.org/packages/policycoreutils/)
- Buildroot (https://git.buildroot.net/buildroot/tree/package/policycoreutils)
- Debian and Ubuntu (https://packages.debian.org/sid/policycoreutils)
- Gentoo (https://packages.gentoo.org/packages/sys-apps/policycoreutils)
- RHEL and Fedora (https://src.fedoraproject.org/rpms/policycoreutils)
- Yocto Project (http://git.yoctoproject.org/cgit/cgit.cgi/meta-selinux/tree/recipes-security/selinux)
- and many more (https://repology.org/project/policycoreutils/versions)
Building and testing
Build dependencies on Fedora:
# For C libraries and programs
dnf install \
audit-libs-devel \
bison \
bzip2-devel \
CUnit-devel \
diffutils \
flex \
gcc \
gettext \
glib2-devel \
make \
libcap-devel \
libcap-ng-devel \
pam-devel \
pcre2-devel \
xmlto
# For Python and Ruby bindings
dnf install \
python3-devel \
ruby-devel \
swig
Build dependencies on Debian:
# For C libraries and programs
apt-get install --no-install-recommends --no-install-suggests \
bison \
flex \
gawk \
gcc \
gettext \
make \
libaudit-dev \
libbz2-dev \
libcap-dev \
libcap-ng-dev \
libcunit1-dev \
libglib2.0-dev \
libpcre2-dev \
pkgconf \
python3 \
python3-distutils \
systemd \
xmlto
# For Python and Ruby bindings
apt-get install --no-install-recommends --no-install-suggests \
python3-dev \
ruby-dev \
swig
To build and install everything under a private directory, run:
make clean distclean
make DESTDIR=~/obj install install-rubywrap install-pywrap
On Debian PYTHON_SETUP_ARGS=--install-layout=deb needs to be set when installing the python wrappers in order to create the correct python directory structure.
To run tests with the built libraries and programs, several paths (relative to $DESTDIR) need to be added to variables $LD_LIBRARY_PATH, $PATH and $PYTHONPATH.
This can be done using ./scripts/env_use_destdir:
DESTDIR=~/obj ./scripts/env_use_destdir make test
Some tests require the reference policy to be installed (for example in python/sepolgen).
In order to run these ones, instructions similar to the ones in section install of ./.travis.yml can be executed.
To install as the default system libraries and binaries (overwriting any previously installed ones - dangerous!), on x86_64, run:
make LIBDIR=/usr/lib64 SHLIBDIR=/lib64 install install-pywrap relabel
or on x86 (32-bit), run:
make install install-pywrap relabel
This may render your system unusable if the upstream SELinux userspace lacks library functions or other dependencies relied upon by your distribution. If it breaks, you get to keep both pieces.
Setting CFLAGS
Setting CFLAGS during the make process will cause the omission of many defaults. While the project strives to provide a reasonable set of default flags, custom CFLAGS could break the build, or have other undesired changes on the build output. Thus, be very careful when setting CFLAGS. CFLAGS that are encouraged to be set when overriding are:
- -fno-semantic-interposition for gcc or compilers that do not do this. clang does this by default. clang-10 and up will support passing this flag, but ignore it. Previous clang versions fail.
macOS
To install libsepol on macOS (mainly for policy analysis):
cd libsepol; make PREFIX=/usr/local install
This requires GNU coreutils:
brew install coreutils