when called with the setid bit change euid to uid sooner to make sure that we can access our own files even when we dropped most capabilities. (Closes #21)

git-svn-id: file:///home/lennart/svn/public/pulseaudio/trunk@1455 fefdeb5f-60dc-0310-8127-8f9354f1896f

src/daemon/caps.c

@@ -35,6 +35,9 @@
 #ifdef HAVE_SYS_CAPABILITY_H
 #include <sys/capability.h>
 #endif
+#ifdef HAVE_SYS_PRCTL_H
+#include <sys/prctl.h>
+#endif
 
 #include <pulsecore/core-error.h>
 
@@ -76,35 +79,31 @@ void pa_drop_root(void) {
 
 #endif
 
-#ifdef HAVE_SYS_CAPABILITY_H
+#if defined(HAVE_SYS_CAPABILITY_H) && defined(HAVE_SYS_PRCTL_H)
 
-/* Limit capabilities set to CAPSYS_NICE */
+/* Limit permitted capabilities set to CAPSYS_NICE */
 int pa_limit_caps(void) {
     int r = -1;
     cap_t caps;
     cap_value_t nice_cap = CAP_SYS_NICE;
 
-    /* Only drop caps when called SUID */
-    if (getuid() == 0)
-        return 0;
-
     caps = cap_init();
     assert(caps);
-
     cap_clear(caps);
-
-    cap_set_flag(caps, CAP_EFFECTIVE, 1, &nice_cap, CAP_SET);
     cap_set_flag(caps, CAP_PERMITTED, 1, &nice_cap, CAP_SET);
 
     if (cap_set_proc(caps) < 0)
         goto fail;
 
+    if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0)
+        goto fail;
+    
     pa_log_info("dropped capabilities successfully.");
-
-    r = 0;
+    
+    r = 1;
 
 fail:
-    cap_free (caps);
+    cap_free(caps);
 
     return r;
 }
@@ -114,24 +113,22 @@ int pa_drop_caps(void) {
     cap_t caps;
     int r = -1;
 
-    /* Only drop caps when called SUID */
-    if (getuid() == 0)
-        return 0;
-
     caps = cap_init();
     assert(caps);
 
     cap_clear(caps);
 
+    prctl(PR_SET_KEEPCAPS, 0, 0, 0, 0);
+    
     if (cap_set_proc(caps) < 0) {
         pa_log("failed to drop capabilities: %s", pa_cstrerror(errno));
         goto fail;
     }
-
+    
     r = 0;
 
 fail:
-    cap_free (caps);
+    cap_free(caps);
 
     return r;
 }

src/daemon/main.c

@@ -329,23 +329,30 @@ int main(int argc, char *argv[]) {
     struct timeval tv;
 #endif
 
-    setlocale(LC_ALL, "");
-
-    pa_limit_caps();
-
 #ifdef HAVE_GETUID
     real_root = getuid() == 0;
     suid_root = !real_root && geteuid() == 0;
-
-    if (suid_root && (pa_own_uid_in_group(PA_REALTIME_GROUP, &gid) <= 0 || gid >= 1000)) {
-        pa_log_warn("WARNING: called SUID root, but not in group '"PA_REALTIME_GROUP"'.");
-        pa_drop_root();
-    }
 #else
     real_root = 0;
     suid_root = 0;
 #endif
 
+    if (suid_root) {
+        if (pa_limit_caps() > 0)
+            /* We managed to drop capabilities except the needed
+             * ones. Hence we can drop the uid. */
+            pa_drop_root();
+    }
+
+    setlocale(LC_ALL, "");
+
+    if (suid_root && (pa_own_uid_in_group(PA_REALTIME_GROUP, &gid) <= 0 || gid >= 1000)) {
+        pa_log_warn("WARNING: called SUID root, but not in group '"PA_REALTIME_GROUP"'.");
+        pa_drop_caps();
+        pa_drop_root();
+        suid_root = real_root = 0;
+    }
+
     LTDL_SET_PRELOADED_SYMBOLS();
 
     r = lt_dlinit();
@@ -381,10 +388,10 @@ int main(int argc, char *argv[]) {
     if (conf->high_priority && conf->cmd == PA_CMD_DAEMON)
         pa_raise_priority();
 
-    pa_drop_caps();
-
-    if (suid_root)
+    if (suid_root) {
+        pa_drop_caps();
         pa_drop_root();
+    }
 
     if (conf->dl_search_path)
         lt_dlsetsearchpath(conf->dl_search_path);

src/pulsecore/core-util.c

@@ -51,6 +51,10 @@
 #include <sys/resource.h>
 #endif
 
+#ifdef HAVE_SYS_CAPABILITY_H
+#include <sys/capability.h>
+#endif
+
 #ifdef HAVE_PTHREAD
 #include <pthread.h>
 #endif
@@ -481,7 +485,23 @@ char *pa_strlcpy(char *b, const char *s, size_t l) {
 sensible: set the nice level to -15 and enable realtime scheduling if
 supported.*/
 void pa_raise_priority(void) {
+#if defined(HAVE_SYS_CAPABILITY_H)
+    cap_t caps;
 
+    /* Temporarily acquire CAP_SYS_NICE in the effective set */
+    if ((caps = cap_get_proc())) {
+        cap_t caps_new;
+        cap_value_t nice_cap = CAP_SYS_NICE;
+        
+        if ((caps_new = cap_dup(caps))) {
+            cap_set_flag(caps_new, CAP_EFFECTIVE, 1, &nice_cap, CAP_SET);
+            cap_set_flag(caps_new, CAP_PERMITTED, 1, &nice_cap, CAP_SET);
+            cap_set_proc(caps_new);
+            cap_free(caps_new);
+        }
+    }
+#endif
+    
 #ifdef HAVE_SYS_RESOURCE_H
     if (setpriority(PRIO_PROCESS, 0, NICE_LEVEL) < 0)
         pa_log_warn("setpriority(): %s", pa_cstrerror(errno));
@@ -495,13 +515,13 @@ void pa_raise_priority(void) {
 
         if (sched_getparam(0, &sp) < 0) {
             pa_log("sched_getparam(): %s", pa_cstrerror(errno));
-            return;
+            goto fail;
         }
 
         sp.sched_priority = 1;
         if (sched_setscheduler(0, SCHED_FIFO, &sp) < 0) {
             pa_log_warn("sched_setscheduler(): %s", pa_cstrerror(errno));
-            return;
+            goto fail;
         }
 
         pa_log_info("Successfully enabled SCHED_FIFO scheduling.");
@@ -514,6 +534,16 @@ void pa_raise_priority(void) {
     else
         pa_log_info("Successfully gained high priority class.");
 #endif
+
+fail:
+
+#if defined(HAVE_SYS_CAPABILITY_H)
+    if (caps) {
+        /* Restore original caps */
+        cap_set_proc(caps);
+        cap_free(caps);
+    }
+#endif
 }
 
 /* Reset the priority to normal, inverting the changes made by pa_raise_priority() */