user-util: sysconf_ngroups_max

This hides the iffy interface of sysconf(_SC_NGROUPS_MAX) to simplify
the calllers.

src/basic/socket-util.c

@@ -39,6 +39,7 @@
 #include "strv.h"
 #include "sysctl-util.h"
 #include "tmpfile-util.h"
+#include "user-util.h"
 #include "xattr-util.h"
 
 #if ENABLE_IDN
@@ -914,7 +915,7 @@ int getpeergroups(int fd, gid_t **ret) {
         assert(fd >= 0);
         assert(ret);
 
-        long ngroups_max = sysconf(_SC_NGROUPS_MAX);
+        int ngroups_max = sysconf_ngroups_max();
         if (ngroups_max > 0)
                 n = MAX(n, sizeof(gid_t) * (socklen_t) ngroups_max);
 

src/basic/user-util.c

@@ -1353,6 +1353,19 @@ int lookup_grent_in_files(
         return -ESRCH;
 }
 
+int sysconf_ngroups_max(void) {
+        /* Query sysconf _SC_NGROUPS_MAX. Returns an int because the expected value is 64k
+         * and later on this is used as an int with various glibc consumers. */
+
+        errno = 0;
+        long ngroups_max = sysconf(_SC_NGROUPS_MAX);
+        if (ngroups_max <= 0)
+                return errno_or_else(EOPNOTSUPP);
+        if (ngroups_max > INT_MAX)
+                return -ERANGE;
+        return ngroups_max;
+}
+
 static size_t getgr_buffer_size(void) {
         long bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
         return bufsize <= 0 ? 4096U : (size_t) bufsize;

src/basic/user-util.h

@@ -173,6 +173,8 @@ static inline bool hashed_password_is_locked_or_invalid(const char *password) {
  */
 #define PASSWORD_UNPROVISIONED "!unprovisioned"
 
+int sysconf_ngroups_max(void);
+
 int lookup_pwent_in_files(
                 char * const *files,
                 const char *name,