Merge pull request #5628 from donaldsharp/rtm_getneigh

[mirror_frr.git] / lib / privs.h

diff --git a/lib/privs.h b/lib/privs.h
index 7fe59328b214fc57f4239644f863fbf4bace0d16..db5707d6750a010b165588b82d66f517fb4b7f28 100644 (file)
--- a/lib/privs.h
+++ b/lib/privs.h
@@ -23,6 +23,13 @@
 #ifndef _ZEBRA_PRIVS_H
 #define _ZEBRA_PRIVS_H
 
+#include <pthread.h>
+#include "lib/queue.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* list of zebra capabilities */
 typedef enum {
        ZCAP_SETID,
@@ -50,11 +57,30 @@ typedef enum {
        ZPRIVS_LOWER,
 } zebra_privs_ops_t;
 
+struct zebra_privs_refs_t {
+       STAILQ_ENTRY(zebra_privs_refs_t) entry;
+       pthread_t tid;
+       uint32_t refcount;
+       const char *raised_in_funcname;
+};
+
 struct zebra_privs_t {
        zebra_capabilities_t *caps_p; /* caps required for operation */
        zebra_capabilities_t *caps_i; /* caps to allow inheritance of */
        int cap_num_p;                /* number of caps in arrays */
        int cap_num_i;
+
+       /* Mutex and counter used to avoid race conditions in multi-threaded
+        * processes. If privs status is process-wide, we need to
+        * control changes to the privilege status among threads.
+        * If privs changes are per-thread, we need to be able to
+        * manage that too.
+        */
+       pthread_mutex_t mutex;
+       struct zebra_privs_refs_t process_refs;
+
+       STAILQ_HEAD(thread_refs_q, zebra_privs_refs_t) thread_refs;
+
        const char *user; /* user and group to run as */
        const char *group;
        const char *vty_group; /* group to chown vty socket to */
@@ -81,4 +107,46 @@ extern void zprivs_terminate(struct zebra_privs_t *);
 /* query for runtime uid's and gid's, eg vty needs this */
 extern void zprivs_get_ids(struct zprivs_ids_t *);
 
+/*
+ * Wrapper around zprivs, to be used as:
+ *   frr_with_privs(&privs) {
+ *     ... code ...
+ *     if (error)
+ *       break;         -- break can be used to get out of the block
+ *     ... code ...
+ *   }
+ *
+ * The argument to frr_with_privs() can be NULL to leave privileges as-is
+ * (mostly useful for conditional privilege-raising, i.e.:)
+ *   frr_with_privs(cond ? &privs : NULL) {}
+ *
+ * NB: The code block is always executed, regardless of whether privileges
+ * could be raised or not, or whether NULL was given or not.  This is fully
+ * intentional;  the user may have configured some RBAC or similar that we
+ * are not aware of, but that allows our code to proceed without privileges.
+ *
+ * The point of this wrapper is to prevent accidental bugs where privileges
+ * are elevated but then not dropped.  This can happen when, for example, a
+ * "return", "goto" or "break" in the middle of the elevated-privilege code
+ * skips past the privilege dropping call.
+ *
+ * The macro below uses variable cleanup to drop privileges as soon as the
+ * code block is left in any way (and thus the _privs variable goes out of
+ * scope.)  _once is just a trick to run the loop exactly once.
+ */
+extern struct zebra_privs_t *_zprivs_raise(struct zebra_privs_t *privs,
+                                          const char *funcname);
+extern void _zprivs_lower(struct zebra_privs_t **privs);
+
+#define frr_with_privs(privs)                                               \
+       for (struct zebra_privs_t *_once = NULL,                               \
+                                 *_privs __attribute__(                       \
+                                         (unused, cleanup(_zprivs_lower))) =  \
+                                         _zprivs_raise(privs, __func__);      \
+            _once == NULL; _once = (void *)1)
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _ZEBRA_PRIVS_H */