Fix Linux getlogin{_r,} implementation

The old implementation uses fd 0 to determine the login TTY.  This
was needed because using /dev/tty it is not possible to deduce the
login TTY.  For some time now there is the pseudo-file
/proc/self/loginuid which directly helps us to find the user.  Prefer
using this file.  It also works if stdin is closed, redirected, or
re-opened.

1 files changed, 100 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c b/sysdeps/unix/sysv/linux/getlogin_r.c
new file mode 100644
index 0000000000..d07846ccb8
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/getlogin_r.c
@@ -0,0 +1,100 @@
+/* Copyright (C) 2010 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <pwd.h>
+#include <unistd.h>
+#include <not-cancel.h>
+
+#define STATIC static
+static int getlogin_r_fd0 (char *name, size_t namesize);
+#define getlogin_r getlogin_r_fd0
+#include <sysdeps/unix/getlogin_r.c>
+#undef getlogin_r
+
+
+int
+attribute_hidden
+__getlogin_r_loginuid (name, namesize)
+     char *name;
+     size_t namesize;
+{
+  int fd = open_not_cancel_2 ("/proc/self/loginuid", O_RDONLY);
+  if (fd == -1)
+    return 1;
+
+  ssize_t n = TEMP_FAILURE_RETRY (read_not_cancel (fd, name, namesize));
+  close_not_cancel_no_status (fd);
+
+  uid_t uid;
+  char *endp;
+  if (n <= 0
+      || (uid = strtoul (name, &endp, 10), endp == name || *endp != '\0'))
+    return 1;
+
+  size_t buflen = 1024;
+  char *buf = alloca (buflen);
+  bool use_malloc = false;
+  struct passwd pwd;
+  struct passwd *tpwd;
+  int res;
+
+  while ((res = __getpwuid_r (uid, &pwd, buf, buflen, &tpwd)) != 0)
+    if (__libc_use_alloca (2 * buflen))
+      extend_alloca (buf, buflen, 2 * buflen);
+    else
+      {
+	buflen *= 2;
+	char *newp = realloc (use_malloc ? buf : NULL, buflen);
+	if (newp == NULL)
+	  {
+	  fail:
+	    if (use_malloc)
+	      free (buf);
+	    return 1;
+	  }
+	buf = newp;
+	use_malloc = true;
+      }
+
+  if (tpwd == NULL)
+    goto fail;
+
+  strncpy (name, pwd.pw_name, namesize - 1);
+  name[namesize - 1] = '\0';
+
+  if (use_malloc)
+    free (buf);
+
+  return 0;
+}
+
+
+/* Return the login name of the user, or NULL if it can't be determined.
+   The returned pointer, if not NULL, is good only until the next call.  */
+
+int
+getlogin_r (name, namesize)
+     char *name;
+     size_t namesize;
+{
+  if (__getlogin_r_loginuid (name, namesize) == 0)
+    return 0;
+
+  return getlogin_r_fd0 (name, namesize);
+}
+libc_hidden_def (getlogin_r)