Update from Gnulib by running admin/merge-gnulib

1 files changed, 54 insertions, 128 deletions

diff --git a/lib/tempname.c b/lib/tempname.c
index 5adfe629a88..11b4796b34b 100644
--- a/lib/tempname.c
+++ b/lib/tempname.c
@@ -20,16 +20,10 @@
 # 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
@@ -43,27 +37,23 @@
 # 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>
 #include <time.h>
 
 #if _LIBC
-# define struct_stat64 struct stat64
-# define __secure_getenv __libc_secure_getenv
+# define struct_stat64 struct __stat64_t64
 #else
 # define struct_stat64 struct stat
 # define __gen_tempname gen_tempname
 # define __mkdir mkdir
 # define __open open
-# define __lstat64(file, buf) lstat (file, buf)
-# define __stat64(file, buf) stat (file, buf)
+# define __lstat64_time64(file, buf) lstat (file, buf)
 # define __getrandom getrandom
 # define __clock_gettime64 clock_gettime
 # define __timespec64 timespec
@@ -77,100 +67,56 @@ 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)
 
-#if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME)
-# define HAS_CLOCK_ENTROPY true
-#else
-# define HAS_CLOCK_ENTROPY false
-#endif
+/* 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 HAS_CLOCK_ENTROPY
-  /* 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 (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;
+  *r = mix_random_values (v, clock ());
+  return false;
 }
-#endif /* _LIBC */
 
 #if _LIBC
 static int try_tempname_len (char *, int, void *, int (*) (char *, void *),
@@ -197,7 +143,7 @@ try_nocreate (char *tmpl, _GL_UNUSED void *flags)
 {
   struct_stat64 st;
 
-  if (__lstat64 (tmpl, &st) == 0 || errno == EOVERFLOW)
+  if (__lstat64_time64 (tmpl, &st) == 0 || errno == EOVERFLOW)
     __set_errno (EEXIST);
   return errno == ENOENT ? 0 : -1;
 }
@@ -267,32 +213,17 @@ 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);
-
-#if !HAS_CLOCK_ENTROPY
-  /* Arrange gen_tempname to return less predictable file names on
-     systems lacking clock entropy <https://bugs.gnu.org/57129>.  */
-  static random_value prev_v;
-  v ^= prev_v;
-#endif
+  /* 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
-     more 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);
@@ -312,18 +243,16 @@ 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--;
         }
 
@@ -331,9 +260,6 @@ try_tempname_len (char *tmpl, int suffixlen, void *args,
       if (fd >= 0)
         {
           __set_errno (save_errno);
-#if !HAS_CLOCK_ENTROPY
-          prev_v = v;
-#endif
           return fd;
         }
       else if (errno != EEXIST)