getlogin_r: return early when linux sentinel value is set

When there is no login uid Linux sets /proc/self/loginid to the sentinel
value of, (uid_t) -1. If this is set we can return early and avoid
needlessly looking up the sentinel value in any configured nss
databases.

Checked on aarch64-linux-gnu.

	* sysdeps/unix/sysv/linux/getlogin_r.c (__getlogin_r_loginuid): Return
	early when linux sentinel value is set.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit cc8a1620eb97ccddd337d157263c13c57b39ab71)

diff --git a/ChangeLog b/ChangeLog
index 89ecd49d19a39668931e2eef72c42e3847c9747e..670c6d94b8cee241c8f1475e9eda7019f8ec85a2 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-27  Jesse Hathaway  <jesse@mbuki-mvuki.org>
+
+       * sysdeps/unix/sysv/linux/getlogin_r.c (__getlogin_r_loginuid): Return
+       early when linux sentinel value is set.
+
 2018-03-27  Andreas Schwab  <schwab@suse.de>
 
        [BZ #23005]

diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c b/sysdeps/unix/sysv/linux/getlogin_r.c
index 84c51d0ecd143541112b57ae4932876b2c08fced..7a814ea92f1481bfbeacbf1a0c33ecf2cbced694 100644 (file)
--- a/sysdeps/unix/sysv/linux/getlogin_r.c
+++ b/sysdeps/unix/sysv/linux/getlogin_r.c
@@ -54,6 +54,15 @@ __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, (uid_t) -1, so check if that value is set and return early to
+     avoid making unneeded nss lookups. */
+  if (uid == (uid_t) -1)
+    {
+      __set_errno (ENXIO);
+      return ENXIO;
+    }
+
   size_t buflen = 1024;
   char *buf = alloca (buflen);
   bool use_malloc = false;