339 lines
13 KiB
Diff
339 lines
13 KiB
Diff
From 7529d06dbe7ac4c1cb41a4fb8e32e3b96be72075 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
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Date: Wed, 4 Oct 2023 16:38:12 +0200
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Subject: [PATCH] PGP: Set a default creation SELinux labels on GnuPG
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directories
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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libdnf used to precreate the directory in /run/user to make sure
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a GnuPG agent executed by GPGME library places its socket there.
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The directories there are normally created and removed by systemd
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(logind PAM session). libdnf created them for a case when a package
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manager is invoked out of systemd session, before the super user logs
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in. E.g. by a timer job to cache repository metadata.
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A problem was when this out-of-session process was a SELinux-confined
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process creating files with its own SELinux label different from a DNF
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program. Then the directory was created with a SELinux label different
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from the one expected by systemd and when logging out a corresponding
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user, the mismatching label clashed with systemd.
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The same issue was with temporary GnuPG home directories created by
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libdnf under /tmp.
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This patch fixes both the isseus by restoring a SELinux label of those
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directories to the label defined in a default SELinux file context
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database.
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Obviously the database cannot have a record for a nonspecific
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/tmp/tmpdir.XXXXXX (a mkdtemp() template) directory names. Therefore
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I changed their names to more specific /tmp/libdnf.XXXXXX. Once
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a SELinux policy updates the database, directories under /tmp will get
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a correct label.
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There is yet another problem with accessing /var/cache/dnf/*/pubring,
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but that seems to be pure SELinux policy problem.
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This patch adds a new -DENABLE_SELINUX=OFF CMake option to disable the
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new dependency on libselinux. A default behavior is to support SELinux.
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Implementation details:
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I used selabel_lookup() + setfscreatecon() + mkdtemp()
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+ setfscreatecon() sequence instead of mkdtemp()
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+ selinux_restorecon() sequence because the later polutes stderr if
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a SELinux policy does not define the default context. One could
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supress stderr messages with selinux_set_callback(), but its effect
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cannot be restored.
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I also kept the sequence in one function and reused it for creating
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/run/user/$PID directories because the code is simpler than spliting
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the function into three parts.
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https://issues.redhat.com/browse/RHEL-6421
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Signed-off-by: Petr Písař <ppisar@redhat.com>
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---
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CMakeLists.txt | 7 +++
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libdnf.spec | 11 +++-
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libdnf/CMakeLists.txt | 4 ++
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libdnf/repo/Repo.cpp | 124 ++++++++++++++++++++++++++++++++++++++----
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4 files changed, 132 insertions(+), 14 deletions(-)
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diff --git a/CMakeLists.txt b/CMakeLists.txt
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index 405dc4e8..cc550ddb 100644
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--- a/CMakeLists.txt
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+++ b/CMakeLists.txt
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@@ -35,6 +35,7 @@ option(WITH_ZCHUNK "Build with zchunk support" ON)
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option(ENABLE_RHSM_SUPPORT "Build with Red Hat Subscription Manager support?" OFF)
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option(ENABLE_SOLV_URPMREORDER "Build with support for URPM-like solution reordering?" OFF)
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option(WITH_TESTS "Enables unit tests" ON)
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+option(ENABLE_SELINUX "Restore SELinux labels on GnuPG directories" ON)
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# build options - debugging
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@@ -83,6 +84,12 @@ if(ENABLE_RHSM_SUPPORT)
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include_directories(${RHSM_INCLUDE_DIRS})
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endif()
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+if(ENABLE_SELINUX)
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+ pkg_check_modules(SELINUX REQUIRED libselinux)
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+ include_directories(${SELINUX_INCLUDE_DIRS})
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+ add_definitions(-DENABLE_SELINUX=1)
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+endif()
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+
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# glibc: check if fnmatch.h has FNM_CASEFOLD symbol
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include(CheckSymbolExists)
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diff --git a/libdnf.spec b/libdnf.spec
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index 41df982c..09b5a89d 100644
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--- a/libdnf.spec
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+++ b/libdnf.spec
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@@ -42,6 +42,8 @@
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%bcond_with rhsm
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%endif
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+%bcond_without selinux
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+
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%if 0%{?rhel}
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%bcond_with zchunk
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%else
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@@ -83,6 +85,9 @@ BuildRequires: pkgconfig(zck) >= 0.9.11
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BuildRequires: pkgconfig(sqlite3)
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BuildRequires: pkgconfig(json-c)
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BuildRequires: pkgconfig(cppunit)
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+%if %{with selinux}
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+BuildRequires: pkgconfig(libselinux)
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+%endif
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BuildRequires: pkgconfig(modulemd-2.0) >= %{libmodulemd_version}
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BuildRequires: pkgconfig(smartcols)
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BuildRequires: gettext
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@@ -204,7 +209,8 @@ pushd build-py2
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%define __builddir build-py2
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%endif
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%cmake -DPYTHON_DESIRED:FILEPATH=%{__python2} -DWITH_MAN=OFF ../ %{!?with_zchunk:-DWITH_ZCHUNK=OFF} %{!?with_valgrind:-DDISABLE_VALGRIND=1} %{_cmake_opts} -DLIBDNF_MAJOR_VERSION=%{libdnf_major_version} -DLIBDNF_MINOR_VERSION=%{libdnf_minor_version} -DLIBDNF_MICRO_VERSION=%{libdnf_micro_version} \
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- -DWITH_SANITIZERS=%{?with_sanitizers:ON}%{!?with_sanitizers:OFF}
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+ -DWITH_SANITIZERS=%{?with_sanitizers:ON}%{!?with_sanitizers:OFF} \
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+ -DENABLE_SELINUX=%{?with_selinux:ON}%{!?with_selinux:OFF}
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%make_build
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popd
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%endif
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@@ -218,7 +224,8 @@ pushd build-py3
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%define __builddir build-py3
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%endif
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%cmake -DPYTHON_DESIRED:FILEPATH=%{__python3} -DWITH_GIR=0 -DWITH_MAN=0 -Dgtkdoc=0 ../ %{!?with_zchunk:-DWITH_ZCHUNK=OFF} %{!?with_valgrind:-DDISABLE_VALGRIND=1} %{_cmake_opts} -DLIBDNF_MAJOR_VERSION=%{libdnf_major_version} -DLIBDNF_MINOR_VERSION=%{libdnf_minor_version} -DLIBDNF_MICRO_VERSION=%{libdnf_micro_version} \
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- -DWITH_SANITIZERS=%{?with_sanitizers:ON}%{!?with_sanitizers:OFF}
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+ -DWITH_SANITIZERS=%{?with_sanitizers:ON}%{!?with_sanitizers:OFF} \
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+ -DENABLE_SELINUX=%{?with_selinux:ON}%{!?with_selinux:OFF}
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%make_build
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popd
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%endif
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diff --git a/libdnf/CMakeLists.txt b/libdnf/CMakeLists.txt
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index 9e71d139..3c82ec3a 100644
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--- a/libdnf/CMakeLists.txt
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+++ b/libdnf/CMakeLists.txt
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@@ -88,6 +88,10 @@ if(ENABLE_RHSM_SUPPORT)
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target_link_libraries(libdnf ${RHSM_LIBRARIES})
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endif()
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+if(ENABLE_SELINUX)
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+ target_link_libraries(libdnf ${SELINUX_LIBRARIES})
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+endif()
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+
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set(DNF_SO_VERSION 2)
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set_target_properties(libdnf PROPERTIES OUTPUT_NAME "dnf")
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set_target_properties(libdnf PROPERTIES SOVERSION ${DNF_SO_VERSION})
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diff --git a/libdnf/repo/Repo.cpp b/libdnf/repo/Repo.cpp
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index 9959a73a..16f15195 100644
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--- a/libdnf/repo/Repo.cpp
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+++ b/libdnf/repo/Repo.cpp
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@@ -51,6 +51,11 @@
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#include <gpgme.h>
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+#if ENABLE_SELINUX
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+#include <selinux/selinux.h>
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+#include <selinux/label.h>
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+#endif
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+
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#include <solv/chksum.h>
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#include <solv/repo.h>
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#include <solv/util.h>
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@@ -651,6 +656,81 @@ std::unique_ptr<LrHandle> Repo::Impl::lrHandleInitRemote(const char *destdir)
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return h;
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}
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+/*
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+ * @brief Create a temporary directory.
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+ *
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+ * Creates a temporary directory with 0700 mode attempting to set a proper
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+ * SELinux file context. Encountered errors are logged at debug level to
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+ * a global logger.
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+ *
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+ * @param name_template As an input value it is a template according to
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+ * mkdtemp(3). As an output value it will contain the created directory name.
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+ *
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+ * @return 0 if the directory was created, -1 if it wasn't. SELinux failures
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+ * are not considered an error.
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+ */
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+static int create_temporary_directory(char *name_template) {
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+ auto logger(Log::getLogger());
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+ int saved_errno = errno;
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+ int retval = 0;
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+#if ENABLE_SELINUX
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+ char *old_default_context = NULL;
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+ char *new_default_context = NULL;
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+ int old_default_context_was_retrieved = 0;
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+ struct selabel_handle *labeling_handle = NULL;
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+
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+ /* A purpose of this piece of code is to deal with applications whose
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+ * security policy overrides a file context for temporary files but don't
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+ * know that libdnf executes GnuPG which expects a default file context. */
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+ if (0 == getfscreatecon(&old_default_context)) {
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+ old_default_context_was_retrieved = 1;
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+ } else {
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+ logger->debug(tfm::format("Failed to retrieve a default SELinux context"));
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+ }
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+
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+ labeling_handle = selabel_open(SELABEL_CTX_FILE, NULL, 0);
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+ if (NULL == labeling_handle) {
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+ logger->debug(tfm::format("Failed to open a SELinux labeling handle: %s",
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+ strerror(errno)));
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+ } else {
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+ if (selabel_lookup(labeling_handle, &new_default_context, name_template, 0700)) {
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+ /* Here we could hard-code "system_u:object_r:user_tmp_t:s0", but
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+ * that value should be really defined in default file context
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+ * SELinux policy. Only log that the policy is incpomplete. */
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+ logger->debug(tfm::format("Failed to look up a default SELinux label for \"%s\"",
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+ name_template));
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+ } else {
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+ if (setfscreatecon(new_default_context)) {
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+ logger->debug(tfm::format("Failed to set default SELinux context to \"%s\"",
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+ new_default_context));
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+ }
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+ freecon(new_default_context);
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+ }
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+ selabel_close(labeling_handle);
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+ }
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+#endif
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+
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+ /* mkdtemp() assures 0700 mode. */
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+ if (NULL == mkdtemp(name_template)) {
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+ saved_errno = errno;
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+ logger->debug(tfm::format("Failed to create a directory \"%s\": %s",
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+ name_template, strerror(errno)));
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+ retval = -1;
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+ }
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+
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+#if ENABLE_SELINUX
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+ if (old_default_context_was_retrieved) {
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+ if (setfscreatecon(old_default_context)) {
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+ logger->debug(tfm::format("Failed to restore a default SELinux context"));
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+ }
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+ }
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+ freecon(old_default_context);
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+#endif
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+
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+ errno = saved_errno;
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+ return retval;
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+}
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+
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static void gpgImportKey(gpgme_ctx_t context, int keyFd)
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{
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auto logger(Log::getLogger());
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@@ -705,8 +785,8 @@ static std::vector<Key> rawkey2infos(int fd) {
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std::unique_ptr<std::remove_pointer<gpgme_ctx_t>::type> context(ctx);
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// set GPG home dir
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- char tmpdir[] = "/tmp/tmpdir.XXXXXX";
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- if (!mkdtemp(tmpdir)) {
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+ char tmpdir[] = "/tmp/libdnf.XXXXXX";
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+ if (create_temporary_directory(tmpdir)) {
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const char * errTxt = strerror(errno);
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throw RepoError(tfm::format(_("Cannot create repo temporary directory \"%s\": %s"),
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tmpdir, errTxt));
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@@ -859,6 +939,13 @@ std::vector<Key> Repo::Impl::retrieve(const std::string & url)
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* would cause a race condition with calling gpgme_release(), see [2], [3],
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* [4].
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*
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+ * Current solution precreating /run/user/$UID showed problematic when this
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+ * library was used out of a systemd-logind session from a programm with an
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+ * unexpected SELinux context. Then /run/user/$UID, normally maintained by
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+ * systemd, was assigned a SELinux label unexpected by systemd causing errors
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+ * on a user logout [5]. We remedy it by restoring the label according to
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+ * a file context policy.
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+ *
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* Since the agent doesn't clean up its sockets properly, by creating this
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* directory we make sure they are in a place that is not causing trouble with
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* container images.
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@@ -867,14 +954,27 @@ std::vector<Key> Repo::Impl::retrieve(const std::string & url)
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* [2] https://bugzilla.redhat.com/show_bug.cgi?id=1769831
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* [3] https://github.com/rpm-software-management/microdnf/issues/50
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* [4] https://bugzilla.redhat.com/show_bug.cgi?id=1781601
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+ * [5] https://issues.redhat.com/browse/RHEL-6421
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*/
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static void ensure_socket_dir_exists() {
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auto logger(Log::getLogger());
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+ char tmpdir[] = "/run/user/libdnf.XXXXXX";
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std::string dirname = "/run/user/" + std::to_string(getuid());
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- int res = mkdir(dirname.c_str(), 0700);
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- if (res != 0 && errno != EEXIST) {
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- logger->debug(tfm::format("Failed to create directory \"%s\": %d - %s",
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- dirname, errno, strerror(errno)));
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+
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+ /* create_temporary_directory() assures 0700 mode and tries its best to
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+ * correct a SELinux label. */
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+ if (create_temporary_directory(tmpdir)) {
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+ return;
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+ }
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+
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+ /* Set the desired name. */
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+ if (rename(tmpdir, dirname.c_str())) {
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+ if (errno != EEXIST && errno != ENOTEMPTY && errno != EBUSY) {
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+ logger->debug(tfm::format("Failed to rename \"%s\" directory to \"%s\": %s",
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+ tmpdir, dirname, strerror(errno)));
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+ }
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+ rmdir(tmpdir);
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+ return;
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}
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}
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@@ -1163,8 +1263,8 @@ void Repo::Impl::addCountmeFlag(LrHandle *handle) {
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bool Repo::Impl::isMetalinkInSync()
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{
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auto logger(Log::getLogger());
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- char tmpdir[] = "/tmp/tmpdir.XXXXXX";
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- if (!mkdtemp(tmpdir)) {
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+ char tmpdir[] = "/tmp/libdnf.XXXXXX";
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+ if (create_temporary_directory(tmpdir)) {
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const char * errTxt = strerror(errno);
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throw RepoError(tfm::format(_("Cannot create repo temporary directory \"%s\": %s"),
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tmpdir, errTxt));
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@@ -1237,8 +1337,8 @@ bool Repo::Impl::isRepomdInSync()
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{
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auto logger(Log::getLogger());
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LrYumRepo *yum_repo;
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- char tmpdir[] = "/tmp/tmpdir.XXXXXX";
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- if (!mkdtemp(tmpdir)) {
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+ char tmpdir[] = "/tmp/libdnf.XXXXXX";
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+ if (create_temporary_directory(tmpdir)) {
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const char * errTxt = strerror(errno);
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throw RepoError(tfm::format(_("Cannot create repo temporary directory \"%s\": %s"),
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tmpdir, errTxt));
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@@ -1280,8 +1380,8 @@ void Repo::Impl::fetch(const std::string & destdir, std::unique_ptr<LrHandle> &&
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throw RepoError(tfm::format(_("Cannot create repo destination directory \"%s\": %s"),
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destdir, errTxt));
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}
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- auto tmpdir = destdir + "/tmpdir.XXXXXX";
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- if (!mkdtemp(&tmpdir.front())) {
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+ auto tmpdir = destdir + "/libdnf.XXXXXX";
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+ if (create_temporary_directory(&tmpdir.front())) {
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const char * errTxt = strerror(errno);
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throw RepoError(tfm::format(_("Cannot create repo temporary directory \"%s\": %s"),
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tmpdir.c_str(), errTxt));
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--
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2.41.0
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