su: more robust getpwuid() for GNU Hurt [coreutils 71b7ddc]

Let's support GNU Hurd over-engineering where a process can exist
without UID and getuid() returns -1 and sets errno.

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/login-utils/su-common.c b/login-utils/su-common.c
index d1fecd701..c0bb5289f 100644
--- a/login-utils/su-common.c
+++ b/login-utils/su-common.c
@@ -129,6 +129,26 @@ static struct option const longopts[] =
   {NULL, 0, NULL, 0}
 };
 
+
+static struct passwd *
+current_getpwuid(void)
+{
+  uid_t ruid;
+
+  /* GNU Hurd implementation has an extension where a process can exist in a
+   * non-conforming environment, and thus be outside the realms of POSIX
+   * process identifiers; on this platform, getuid() fails with a status of
+   * (uid_t)(-1) and sets errno if a program is run from a non-conforming
+   * environment.
+   *
+   * http://austingroupbugs.net/view.php?id=511
+   */
+  errno = 0;
+  ruid = getuid ();
+
+  return errno == 0 ? getpwuid (ruid) : NULL;
+}
+
 /* Log the fact that someone has run su to the user given by PW;
    if SUCCESSFUL is true, they gave the correct password, etc.  */
 
@@ -145,8 +165,8 @@ log_su (struct passwd const *pw, bool successful)
     {
       /* getlogin can fail -- usually due to lack of utmp entry.
 	 Resort to getpwuid.  */
-      struct passwd *pwd = getpwuid (getuid ());
-      old_user = (pwd ? pwd->pw_name : "");
+      struct passwd *pwd = current_getpwuid();
+      old_user = pwd ? pwd->pw_name : "";
     }
   tty = ttyname (STDERR_FILENO);
   if (!tty)
@@ -353,7 +373,7 @@ authenticate (const struct passwd *pw)
 	goto done;
     }
 
-  lpw = getpwuid (getuid ());
+  lpw = current_getpwuid ();
   if (lpw && lpw->pw_name)
     {
       retval = pam_set_item (pamh, PAM_RUSER, (const void *) lpw->pw_name);