[PATCH v4] posix: Sync tempname with gnulib

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

The gnulib version contains an important change (9ce573cde), which
fixes some problems with multithreading, entropy loss, and ASLR leak
nfo.  It also fixes a current issue where getrandom is not being used
on some new files generation (only for __GT_NOCREATE on first try).

The 044bf893ac removed __path_search, which is now moved to another
gnulib shared files (stdio-common/tmpdir.{c,h}) and this patch
also fixes direxists to use __stat64_time64 instead of __xstat64.

The sync also removed the clock fallback, since clock_gettime is
expected to always succeed.

It syncs with gnulib commit 323834962817af7b115187e8c9a833437f8d20ec.

Checked on x86_64-linux-gnu.
---
 SHARED-FILES             |   5 +-
 include/stdio.h          |   5 --
 libio/oldtmpfile.c       |   1 +
 stdio-common/Makefile    |   1 +
 stdio-common/tempnam.c   |   1 +
 stdio-common/tempname.c  |  12 ---
 stdio-common/tmpdir.c    | 163 +++++++++++++++++++++++++++++++++++++
 stdio-common/tmpdir.h    |  28 +++++++
 stdio-common/tmpfile.c   |   1 +
 stdio-common/tmpnam.c    |   1 +
 stdio-common/tmpnam_r.c  |   1 +
 sysdeps/posix/tempname.c | 171 +++++++++++++--------------------------
 12 files changed, 258 insertions(+), 132 deletions(-)
 create mode 100644 stdio-common/tmpdir.c
 create mode 100644 stdio-common/tmpdir.h

diff --git a/SHARED-FILES b/SHARED-FILES
index 9c8e715fb5..179130d567 100644
--- a/SHARED-FILES
+++ b/SHARED-FILES
@@ -111,6 +111,9 @@ gnulib:
   string/strstr.c
   string/strtok_r.c
   string/strverscmp.c
+  # Merged from gnulib 2024-04-08 (gnulib commit 3238349628)
+  stdio-common/tmpdir.c
+  stdio-common/tmpdir.h
   sysdeps/generic/pty-private.h
   sysdeps/generic/siglist.h
   sysdeps/posix/euidaccess.c
@@ -118,7 +121,7 @@ gnulib:
   sysdeps/posix/getcwd.c
   sysdeps/posix/pwrite.c
   sysdeps/posix/spawni.c
-  # Merged from gnulib 2014-6-23
+  # Merged from gnulib 2024-04-08 (gnulib commit 3238349628)
   sysdeps/posix/tempname.c
   # Merged from gnulib 2014-6-27
   time/mktime.c
diff --git a/include/stdio.h b/include/stdio.h
index 24f1652f19..e48d709919 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -156,11 +156,6 @@ extern FILE *__old_tmpfile (void);
 
 #  include <bits/types/wint_t.h>
 
-/* Generate a unique file name (and possibly open it).  */
-extern int __path_search (char *__tmpl, size_t __tmpl_len,
-			  const char *__dir, const char *__pfx,
-			  int __try_tempdir) attribute_hidden;
-
 extern int __gen_tempname (char *__tmpl, int __suffixlen, int __flags,
 			   int __kind) attribute_hidden;
 /* The __kind argument to __gen_tempname may be one of: */
diff --git a/libio/oldtmpfile.c b/libio/oldtmpfile.c
index af467a6e5a..f09ee0600c 100644
--- a/libio/oldtmpfile.c
+++ b/libio/oldtmpfile.c
@@ -22,6 +22,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <iolibio.h>
+#include <stdio-common/tmpdir.h>
 
 /* This returns a new stream opened on a temporary file (generated
    by tmpnam).  The file is opened with mode "w+b" (binary read/write).
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 6447b6b444..6bc972af1a 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -92,6 +92,7 @@ routines := \
   sscanf \
   tempnam \
   tempname \
+  tmpdir \
   tmpfile \
   tmpfile64 \
   tmpnam \
diff --git a/stdio-common/tempnam.c b/stdio-common/tempnam.c
index 0f8eaf3535..9e62442451 100644
--- a/stdio-common/tempnam.c
+++ b/stdio-common/tempnam.c
@@ -17,6 +17,7 @@
 
 #include <stdio.h>
 #include <string.h>
+#include "tmpdir.h"
 
 /* Generate a unique temporary filename using up to five characters of
    PFX if it is not NULL.  The directory to put this file in is
diff --git a/stdio-common/tempname.c b/stdio-common/tempname.c
index d88f1c3946..77e695ca5f 100644
--- a/stdio-common/tempname.c
+++ b/stdio-common/tempname.c
@@ -20,18 +20,6 @@
 #include <stdio.h>
 #include <errno.h>
 
-/* Perform the "SVID path search malarkey" on DIR and PFX.  Write a
-   template suitable for use in __gen_tempname into TMPL, bounded
-   by TMPL_LEN. */
-int
-__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
-	       int try_tmpdir)
-{
-  __set_errno (ENOSYS);
-  return -1;
-}
-stub_warning (__path_search)
-
 /* Generate a (hopefully) unique temporary filename
    in DIR (if applicable), using template TMPL.
    KIND determines what to do with that name.  It may be one of:
diff --git a/stdio-common/tmpdir.c b/stdio-common/tmpdir.c
new file mode 100644
index 0000000000..a408bed081
--- /dev/null
+++ b/stdio-common/tmpdir.c
@@ -0,0 +1,163 @@
+/* Copyright (C) 1999, 2001-2002, 2006, 2009-2024 Free Software Foundation,
+   Inc.
+   This file is part of the GNU C Library.
+
+   This file 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 3 of the
+   License, or (at your option) any later version.
+
+   This file 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Extracted from sysdeps/posix/tempname.c.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "tmpdir.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <errno.h>
+#ifndef __set_errno
+# define __set_errno(Val) errno = (Val)
+#endif
+
+#include <stdio.h>
+#ifndef P_tmpdir
+# ifdef _P_tmpdir /* native Windows */
+#  define P_tmpdir _P_tmpdir
+# else
+#  define P_tmpdir "/tmp"
+# endif
+#endif
+
+#include <sys/stat.h>
+
+#if defined _WIN32 && ! defined __CYGWIN__
+# define WIN32_LEAN_AND_MEAN  /* avoid including junk */
+# include <windows.h>
+# include "pathmax.h"
+#endif
+
+#if defined _WIN32 && ! defined __CYGWIN__
+/* Don't assume that UNICODE is not defined.  */
+# undef GetTempPath
+# define GetTempPath GetTempPathA
+#endif
+
+#if _LIBC
+# define struct_stat64 struct __stat64_t64
+#else
+# define struct_stat64 struct stat
+# define __libc_secure_getenv secure_getenv
+# define __stat64_time64(path, buf) stat (path, buf)
+#endif
+
+/* Pathname support.
+   ISSLASH(C)           tests whether C is a directory separator character.
+ */
+#if defined _WIN32 || defined __CYGWIN__ || defined __EMX__ || defined __DJGPP__
+  /* Native Windows, Cygwin, OS/2, DOS */
+# define ISSLASH(C) ((C) == '/' || (C) == '\\')
+#else
+  /* Unix */
+# define ISSLASH(C) ((C) == '/')
+#endif
+
+
+/* Return nonzero if DIR is an existent directory.  */
+static bool
+direxists (const char *dir)
+{
+  struct_stat64 buf;
+  return __stat64_time64 (dir, &buf) == 0 && S_ISDIR (buf.st_mode);
+}
+
+/* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
+   non-null and exists, uses it; otherwise uses the first of $TMPDIR,
+   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
+   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
+   doesn't exist, none of the searched dirs exists, or there's not
+   enough space in TMPL. */
+int
+__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
+	       bool try_tmpdir)
+{
+  const char *d;
+  size_t dlen, plen;
+  bool add_slash;
+
+  if (!pfx || !pfx[0])
+    {
+      pfx = "file";
+      plen = 4;
+    }
+  else
+    {
+      plen = strlen (pfx);
+      if (plen > 5)
+        plen = 5;
+    }
+
+  if (try_tmpdir)
+    {
+      d = __libc_secure_getenv ("TMPDIR");
+      if (d != NULL && direxists (d))
+        dir = d;
+      else if (dir != NULL && direxists (dir))
+        /* nothing */ ;
+      else
+        dir = NULL;
+    }
+  if (dir == NULL)
+    {
+#if defined _WIN32 && ! defined __CYGWIN__
+      char dirbuf[PATH_MAX];
+      DWORD retval;
+
+      /* Find Windows temporary file directory.
+         We try this before P_tmpdir because Windows defines P_tmpdir to "\\"
+         and will therefore try to put all temporary files in the root
+         directory (unless $TMPDIR is set).  */
+      retval = GetTempPath (PATH_MAX, dirbuf);
+      if (retval > 0 && retval < PATH_MAX && direxists (dirbuf))
+        dir = dirbuf;
+      else
+#endif
+      if (direxists (P_tmpdir))
+        dir = P_tmpdir;
+      else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
+        dir = "/tmp";
+      else
+        {
+          __set_errno (ENOENT);
+          return -1;
+        }
+    }
+
+  dlen = strlen (dir);
+#ifdef __VMS
+  add_slash = 0;
+#else
+  add_slash = dlen != 0 && !ISSLASH (dir[dlen - 1]);
+#endif
+
+  /* check we have room for "${dir}/${pfx}XXXXXX\0" */
+  if (tmpl_len < dlen + add_slash + plen + 6 + 1)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  memcpy (tmpl, dir, dlen);
+  sprintf (tmpl + dlen, &"/%.*sXXXXXX"[!add_slash], (int) plen, pfx);
+  return 0;
+}
diff --git a/stdio-common/tmpdir.h b/stdio-common/tmpdir.h
new file mode 100644
index 0000000000..afffafe90a
--- /dev/null
+++ b/stdio-common/tmpdir.h
@@ -0,0 +1,28 @@
+/* Determine a temporary directory.
+   Copyright (C) 2001-2002, 2009-2024 Free Software Foundation, Inc.
+
+   This file 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 3 of the
+   License, or (at your option) any later version.
+
+   This file 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
+   non-null and exists, uses it; otherwise uses the first of $TMPDIR,
+   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
+   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
+   doesn't exist, none of the searched dirs exists, or there's not
+   enough space in TMPL. */
+extern int __path_search (char *tmpl, size_t tmpl_len, const char *dir,
+			  const char *pfx, bool try_tmpdir)
+     attribute_hidden;
diff --git a/stdio-common/tmpfile.c b/stdio-common/tmpfile.c
index 9c49483fca..08cf9284bb 100644
--- a/stdio-common/tmpfile.c
+++ b/stdio-common/tmpfile.c
@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <unistd.h>
+#include "tmpdir.h"
 
 #include <iolibio.h>
 #define __fdopen _IO_fdopen
diff --git a/stdio-common/tmpnam.c b/stdio-common/tmpnam.c
index b02ad952e9..1cff363718 100644
--- a/stdio-common/tmpnam.c
+++ b/stdio-common/tmpnam.c
@@ -17,6 +17,7 @@
 
 #include <stdio.h>
 #include <string.h>
+#include "tmpdir.h"
 
 static char tmpnam_buffer[L_tmpnam];
 
diff --git a/stdio-common/tmpnam_r.c b/stdio-common/tmpnam_r.c
index 2a3598af36..38f9bace9b 100644
--- a/stdio-common/tmpnam_r.c
+++ b/stdio-common/tmpnam_r.c
@@ -16,6 +16,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <stdio.h>
+#include "tmpdir.h"
 
 /* Generate a unique filename in P_tmpdir.  If S is NULL return NULL.
    This makes this function thread safe.  */
diff --git a/sysdeps/posix/tempname.c b/sysdeps/posix/tempname.c
index 2af22386eb..1febbb65ea 100644
--- a/sysdeps/posix/tempname.c
+++ b/sysdeps/posix/tempname.c
@@ -20,16 +20,9 @@
 # include "tempname.h"
 #endif
 
-#include <sys/types.h>
-#include <assert.h>
-#include <stdbool.h>
-
 #include <errno.h>
 
 #include <stdio.h>
-#ifndef P_tmpdir
-# define P_tmpdir "/tmp"
-#endif
 #ifndef TMP_MAX
 # define TMP_MAX 238328
 #endif
@@ -43,12 +36,10 @@
 # error report this to bug-gnulib@gnu.org
 #endif
 
-#include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <fcntl.h>
-#include <stdalign.h>
 #include <stdint.h>
 #include <sys/random.h>
 #include <sys/stat.h>
@@ -56,14 +47,12 @@
 
 #if _LIBC
 # define struct_stat64 struct __stat64_t64
-# define __secure_getenv __libc_secure_getenv
 #else
 # define struct_stat64 struct stat
 # define __gen_tempname gen_tempname
 # define __mkdir mkdir
 # define __open open
 # define __lstat64_time64(file, buf) lstat (file, buf)
-# define __stat64(file, buf) stat (file, buf)
 # define __getrandom getrandom
 # define __clock_gettime64 clock_gettime
 # define __timespec64 timespec
@@ -77,94 +66,58 @@ typedef uint_fast64_t random_value;
 #define BASE_62_DIGITS 10 /* 62**10 < UINT_FAST64_MAX */
 #define BASE_62_POWER (62LL * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62)
 
+/* Return the result of mixing the entropy from R and S.
+   Assume that R and S are not particularly random,
+   and that the result should look randomish to an untrained eye.  */
+
 static random_value
-random_bits (random_value var, bool use_getrandom)
+mix_random_values (random_value r, random_value s)
 {
-  random_value r;
-  /* Without GRND_NONBLOCK it can be blocked for minutes on some systems.  */
-  if (use_getrandom && __getrandom (&r, sizeof r, GRND_NONBLOCK) == sizeof r)
-    return r;
-#if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME)
-  /* Add entropy if getrandom did not work.  */
-  struct __timespec64 tv;
-  __clock_gettime64 (CLOCK_MONOTONIC, &tv);
-  var ^= tv.tv_nsec;
-#endif
-  return 2862933555777941757 * var + 3037000493;
+  /* As this code is used only when high-quality randomness is neither
+     available nor necessary, there is no need for fancier polynomials
+     such as those in the Linux kernel's 'random' driver.  */
+  return (2862933555777941757 * r + 3037000493) ^ s;
 }
 
-#if _LIBC
-/* Return nonzero if DIR is an existent directory.  */
-static int
-direxists (const char *dir)
-{
-  struct_stat64 buf;
-  return __stat64_time64 (dir, &buf) == 0 && S_ISDIR (buf.st_mode);
-}
+/* Set *R to a random value.
+   Return true if *R is set to high-quality value taken from getrandom.
+   Otherwise return false, falling back to a low-quality *R that might
+   depend on S.
 
-/* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
-   non-null and exists, uses it; otherwise uses the first of $TMPDIR,
-   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
-   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
-   doesn't exist, none of the searched dirs exists, or there's not
-   enough space in TMPL. */
-int
-__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
-               int try_tmpdir)
+   This function returns false only when getrandom fails.
+   On GNU systems this should happen only early in the boot process,
+   when the fallback should be good enough for programs using tempname
+   because any attacker likely has root privileges already.  */
+
+static bool
+random_bits (random_value *r, random_value s)
 {
-  const char *d;
-  size_t dlen, plen;
+  /* Without GRND_NONBLOCK it can be blocked for minutes on some systems.  */
+  if (__getrandom (r, sizeof *r, GRND_NONBLOCK) == sizeof *r)
+    return true;
 
-  if (!pfx || !pfx[0])
-    {
-      pfx = "file";
-      plen = 4;
-    }
-  else
-    {
-      plen = strlen (pfx);
-      if (plen > 5)
-        plen = 5;
-    }
+  /* If getrandom did not work, use ersatz entropy based on low-order
+     clock bits.  On GNU systems getrandom should fail only
+     early in booting, when ersatz should be good enough.
+     Do not use ASLR-based entropy, as that would leak ASLR info into
+     the resulting file name which is typically public.
 
-  if (try_tmpdir)
-    {
-      d = __secure_getenv ("TMPDIR");
-      if (d != NULL && direxists (d))
-        dir = d;
-      else if (dir != NULL && direxists (dir))
-        /* nothing */ ;
-      else
-        dir = NULL;
-    }
-  if (dir == NULL)
-    {
-      if (direxists (P_tmpdir))
-        dir = P_tmpdir;
-      else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
-        dir = "/tmp";
-      else
-        {
-          __set_errno (ENOENT);
-          return -1;
-        }
-    }
+     Of course we are in a state of sin here.  */
 
-  dlen = strlen (dir);
-  while (dlen > 1 && dir[dlen - 1] == '/')
-    dlen--;                     /* remove trailing slashes */
+  random_value v = s;
 
-  /* check we have room for "${dir}/${pfx}XXXXXX\0" */
-  if (tmpl_len < dlen + 1 + plen + 6 + 1)
-    {
-      __set_errno (EINVAL);
-      return -1;
-    }
+#if _LIBC || (defined CLOCK_REALTIME && HAVE_CLOCK_GETTIME)
+  struct __timespec64 tv;
+  __clock_gettime64 (CLOCK_REALTIME, &tv);
+  v = mix_random_values (v, tv.tv_sec);
+  v = mix_random_values (v, tv.tv_nsec);
+#endif
 
-  sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
-  return 0;
+#if !_LIBC
+  *r = mix_random_values (v, clock ());
+#endif
+  return false;
 }
-#endif /* _LIBC */
 
 #if _LIBC
 static int try_tempname_len (char *, int, void *, int (*) (char *, void *),
@@ -213,7 +166,7 @@ static const char letters[] =
                         and return a read-write fd.  The file is mode 0600.
    __GT_DIR:            create a directory, which will be mode 0700.
 
-   We use a clever algorithm to get hard-to-predict names. */
+   */
 #ifdef _LIBC
 static
 #endif
@@ -242,7 +195,7 @@ try_tempname_len (char *tmpl, int suffixlen, void *args,
   char *XXXXXX;
   unsigned int count;
   int fd = -1;
-  int save_errno = errno;
+  int saved_errno = errno;
 
   /* A lower bound on the number of temporary files to attempt to
      generate.  The maximum total number of temporary file names that
@@ -261,25 +214,17 @@ try_tempname_len (char *tmpl, int suffixlen, void *args,
   unsigned int attempts = ATTEMPTS_MIN;
 #endif
 
-  /* A random variable.  The initial value is used only the for fallback path
-     on 'random_bits' on 'getrandom' failure.  Its initial value tries to use
-     some entropy from the ASLR and ignore possible bits from the stack
-     alignment.  */
-  random_value v = ((uintptr_t) &v) / alignof (max_align_t);
+  /* A random variable.  */
+  random_value v = 0;
 
-  /* How many random base-62 digits can currently be extracted from V.  */
+  /* A value derived from the random variable, and how many random
+     base-62 digits can currently be extracted from VDIGBUF.  */
+  random_value vdigbuf;
   int vdigits = 0;
 
-  /* Whether to consume entropy when acquiring random bits.  On the
-     first try it's worth the entropy cost with __GT_NOCREATE, which
-     is inherently insecure and can use the entropy to make it a bit
-     less secure.  On the (rare) second and later attempts it might
-     help against DoS attacks.  */
-  bool use_getrandom = tryfunc == try_nocreate;
-
-  /* Least unfair value for V.  If V is less than this, V can generate
-     BASE_62_DIGITS digits fairly.  Otherwise it might be biased.  */
-  random_value const unfair_min
+  /* Least biased value for V.  If V is less than this, V can generate
+     BASE_62_DIGITS unbiased digits.  Otherwise the digits are biased.  */
+  random_value const biased_min
     = RANDOM_VALUE_MAX - RANDOM_VALUE_MAX % BASE_62_POWER;
 
   len = strlen (tmpl);
@@ -299,25 +244,23 @@ try_tempname_len (char *tmpl, int suffixlen, void *args,
         {
           if (vdigits == 0)
             {
-              do
-                {
-                  v = random_bits (v, use_getrandom);
-                  use_getrandom = true;
-                }
-              while (unfair_min <= v);
+              /* Worry about bias only if the bits are high quality.  */
+              while (random_bits (&v, v) && biased_min <= v)
+                continue;
 
+              vdigbuf = v;
               vdigits = BASE_62_DIGITS;
             }
 
-          XXXXXX[i] = letters[v % 62];
-          v /= 62;
+          XXXXXX[i] = letters[vdigbuf % 62];
+          vdigbuf /= 62;
           vdigits--;
         }
 
       fd = tryfunc (tmpl, args);
       if (fd >= 0)
         {
-          __set_errno (save_errno);
+          __set_errno (saved_errno);
           return fd;
         }
       else if (errno != EEXIST)
-- 
2.34.1