Add helpers for getting env vars in a setuid environment

Care must be taken accessing env variables when running
setuid. Introduce a virGetEnvAllowSUID for env vars which
are safe to use in a setuid environment, and another
virGetEnvBlockSUID for vars which are not safe. Also add
a virIsSUID helper method for any other non-env var code
to use.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

bootstrap.conf

@@ -93,6 +93,7 @@ recv
 regex
 random_r
 sched
+secure_getenv
 send
 setenv
 setsockopt

src/libvirt_private.syms

@@ -1859,6 +1859,8 @@ virFindFCHostCapableVport;
 virFormatIntDecimal;
 virGetDeviceID;
 virGetDeviceUnprivSGIO;
+virGetEnvAllowSUID;
+virGetEnvBlockSUID;
 virGetFCHostNameByWWN;
 virGetGroupID;
 virGetGroupList;
@@ -1877,6 +1879,7 @@ virIndexToDiskName;
 virIsCapableFCHost;
 virIsCapableVport;
 virIsDevMapperDevice;
+virIsSUID;
 virManageVport;
 virParseNumber;
 virParseOwnershipIds;

src/util/virutil.c

@@ -2131,3 +2131,42 @@ cleanup:
 
     return rc;
 }
+
+
+/**
+ * virGetEnvBlockSUID:
+ * @name: the environment variable name
+ *
+ * Obtain an environment variable which is unsafe to
+ * use when running setuid. If running setuid, a NULL
+ * value will be returned
+ */
+const char *virGetEnvBlockSUID(const char *name)
+{
+    return secure_getenv(name);
+}
+
+
+/**
+ * virGetEnvBlockSUID:
+ * @name: the environment variable name
+ *
+ * Obtain an environment variable which is safe to
+ * use when running setuid. The value will be returned
+ * even when running setuid
+ */
+const char *virGetEnvAllowSUID(const char *name)
+{
+    return getenv(name);
+}
+
+
+/**
+ * virIsSUID:
+ * Return a true value if running setuid. Does not
+ * check for elevated capabilities bits.
+ */
+bool virIsSUID(void)
+{
+    return getuid() != geteuid();
+}

src/util/virutil.h

@@ -172,4 +172,8 @@ int virCompareLimitUlong(unsigned long long a, unsigned long long b);
 
 int virParseOwnershipIds(const char *label, uid_t *uidPtr, gid_t *gidPtr);
 
+const char *virGetEnvBlockSUID(const char *name);
+const char *virGetEnvAllowSUID(const char *name);
+bool virIsSUID(void);
+
 #endif /* __VIR_UTIL_H__ */