[PATCH] getlogin_r: return early when linux sentinel value is set

[Jesse Hathaway]

When there is no login uid Linux sets /proc/self/loginid to the sentinel
value of 4294967295. If this is set we can return early and avoid
needlessly looking up the sentinel value in any configured nss
databases.

diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
b/sysdeps/unix/sysv/linux/getlogin_r.c
index 73ea14c8f9..43f55a2188 100644
--- a/sysdeps/unix/sysv/linux/getlogin_r.c
+++ b/sysdeps/unix/sysv/linux/getlogin_r.c
@@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
    endp == uidbuf || *endp != '\0'))
     return -1;

+  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
+     value of 4294967295, so check if the value is set and return early to
+     avoid making unneeded nss lookups. */
+  if (uid == 4294967295)
+    return ENXIO;
+
   struct passwd pwd;
   struct passwd *tpwd;
   int result = 0;