selinux: Only call semanage if the context actually changes

https://fedorahosted.org/sssd/ticket/2624

Add a function to query the libsemanage database for a user context and
only update the database if the context differes from the one set on the
server.

Adds talloc dependency to libsss_semanage.

Reviewed-by: Michal Židek <mzidek@redhat.com>
(cherry picked from commit 1e0fa55fb377db788e065de917ba8e149eb56161)
(cherry picked from commit 4d31f2c294db6090047e4d5348322b32ea0aaac1)

4 files changed, 109 insertions, 4 deletions

diff --git a/Makefile.am b/Makefile.am
index 973f8cb35..65b9773d8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -770,10 +770,15 @@ endif
 libsss_util_la_LDFLAGS = -avoid-version
 
 pkglib_LTLIBRARIES += libsss_semanage.la
+libsss_semanage_la_CFLAGS = \
+    $(AM_CFLAGS) \
+    $(TALLOC_CFLAGS) \
+    $(NULL)
 libsss_semanage_la_SOURCES = \
     src/util/sss_semanage.c \
     $(NULL)
 libsss_semanage_la_LIBADD = \
+    $(TALLOC_LIBS) \
     libsss_debug.la \
     $(NULL)
 if BUILD_SEMANAGE
diff --git a/src/providers/ipa/selinux_child.c b/src/providers/ipa/selinux_child.c
index 81c1de877..7c5731d66 100644
--- a/src/providers/ipa/selinux_child.c
+++ b/src/providers/ipa/selinux_child.c
@@ -165,6 +165,29 @@ static int sc_set_seuser(const char *login_name, const char *seuser_name,
     return ret;
 }
 
+static bool seuser_needs_update(struct input_buffer *ibuf)
+{
+    bool needs_update = true;
+    char *db_seuser = NULL;
+    char *db_mls_range = NULL;
+    errno_t ret;
+
+    ret = get_seuser(ibuf, ibuf->username, &db_seuser, &db_mls_range);
+    DEBUG(SSSDBG_TRACE_INTERNAL,
+          "get_seuser: ret: %d seuser: %s mls: %s\n",
+          ret, db_seuser ? db_seuser : "unknown",
+          db_mls_range ? db_mls_range : "unknown");
+    if (ret == EOK && db_seuser && db_mls_range &&
+            strcmp(db_seuser, ibuf->seuser) == 0 &&
+            strcmp(db_mls_range, ibuf->mls_range) == 0) {
+        needs_update = false;
+    }
+
+    talloc_free(db_seuser);
+    talloc_free(db_mls_range);
+    return needs_update;
+}
+
 int main(int argc, const char *argv[])
 {
     int opt;
@@ -177,6 +200,7 @@ int main(int argc, const char *argv[])
     struct input_buffer *ibuf = NULL;
     struct response *resp = NULL;
     ssize_t written;
+    bool needs_update;
 
     struct poptOption long_options[] = {
         POPT_AUTOHELP
@@ -296,10 +320,13 @@ int main(int argc, const char *argv[])
 
     DEBUG(SSSDBG_TRACE_FUNC, "performing selinux operations\n");
 
-    ret = sc_set_seuser(ibuf->username, ibuf->seuser, ibuf->mls_range);
-    if (ret != EOK) {
-        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot set SELinux login context.\n");
-        goto fail;
+    needs_update = seuser_needs_update(ibuf);
+    if (needs_update == true) {
+        ret = sc_set_seuser(ibuf->username, ibuf->seuser, ibuf->mls_range);
+        if (ret != EOK) {
+            DEBUG(SSSDBG_CRIT_FAILURE, "Cannot set SELinux login context.\n");
+            goto fail;
+        }
     }
 
     ret = prepare_response(main_ctx, ret, &resp);
diff --git a/src/util/sss_semanage.c b/src/util/sss_semanage.c
index c0342498c..01a2f41d8 100644
--- a/src/util/sss_semanage.c
+++ b/src/util/sss_semanage.c
@@ -369,6 +369,71 @@ done:
     return ret;
 }
 
+int get_seuser(TALLOC_CTX *mem_ctx, const char *login_name,
+               char **_seuser, char **_mls_range)
+{
+    errno_t ret;
+    const char *seuser;
+    const char *mls_range;
+    semanage_handle_t *sm_handle = NULL;
+    semanage_seuser_t *sm_user = NULL;
+    semanage_seuser_key_t *sm_key = NULL;
+
+    sm_handle = sss_semanage_init();
+    if (sm_handle == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot create SELinux handle\n");
+        ret = EIO;
+        goto done;
+    }
+
+    ret = semanage_seuser_key_create(sm_handle, login_name, &sm_key);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot create key for %s\n", login_name);
+        ret = EIO;
+        goto done;
+    }
+
+    ret = semanage_seuser_query(sm_handle, sm_key, &sm_user);
+    if (ret < 0) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot query for %s\n", login_name);
+        ret = EIO;
+        goto done;
+    }
+
+    seuser = semanage_seuser_get_sename(sm_user);
+    if (seuser != NULL) {
+        *_seuser = talloc_strdup(mem_ctx, seuser);
+        if (*_seuser == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+        DEBUG(SSSDBG_OP_FAILURE,
+              "SELinux user for %s: %s\n", login_name, *_seuser);
+    } else {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot get sename for %s\n", login_name);
+    }
+
+    mls_range = semanage_seuser_get_mlsrange(sm_user);
+    if (mls_range != NULL) {
+        *_mls_range = talloc_strdup(mem_ctx, mls_range);
+        if (*_mls_range == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+        DEBUG(SSSDBG_OP_FAILURE,
+              "SELinux range for %s: %s\n", login_name, *_mls_range);
+    } else {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot get mlsrange for %s\n", login_name);
+    }
+
+    ret = EOK;
+done:
+    semanage_seuser_key_free(sm_key);
+    semanage_seuser_free(sm_user);
+    sss_semanage_close(sm_handle);
+    return ret;
+}
+
 #else /* HAVE_SEMANAGE */
 int set_seuser(const char *login_name, const char *seuser_name,
                const char *mls)
@@ -380,4 +445,10 @@ int del_seuser(const char *login_name)
 {
     return EOK;
 }
+
+int get_seuser(TALLOC_CTX *mem_ctx, const char *login_name,
+               char **_seuser, char **_mls_range)
+{
+    return EOK;
+}
 #endif  /* HAVE_SEMANAGE */
diff --git a/src/util/util.h b/src/util/util.h
index 91df09914..81a8709d6 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -642,6 +642,8 @@ errno_t restore_creds(struct sss_creds *saved_creds);
 int set_seuser(const char *login_name, const char *seuser_name,
                const char *mlsrange);
 int del_seuser(const char *login_name);
+int get_seuser(TALLOC_CTX *mem_ctx, const char *login_name,
+               char **_seuser, char **_mls_range);
 
 /* convert time from generalized form to unix time */
 errno_t sss_utc_to_time_t(const char *str, const char *format, time_t *unix_time);