diff mbox series

posix: Sync tempname with gnulib (BZ 30958)

Message ID 20231010194325.2443369-1-adhemerval.zanella@linaro.org
State Superseded
Headers show
Series posix: Sync tempname with gnulib (BZ 30958) | expand

Commit Message

Adhemerval Zanella Netto Oct. 10, 2023, 7:43 p.m. UTC
The gnulib version contains an important fix (9ce573cde), which fixes
some problems multithreading, entropy loss, and ASLR info.  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 its own
sysdeps/posix/pathsearch.c implementation.

The bug report is not really againt glibc (the reported stated it
checked on mingw); and Linux is unlikely to show the same issue
even if ASLR is disabled (it might occur without ASLR and with a
very imprecise clock).

It syncs with gnulib commit 32a72f45374c9a36afa574d1a08bb98090270012.

Checked on x86_64-linux-gnu.
---
 include/time.h                  |   2 +
 stdio-common/Makefile           |   1 +
 stdio-common/pathsearch.c       |  30 ++++++
 stdio-common/tempname.c         |  12 ---
 sysdeps/mach/hurd/clock.c       |   1 +
 sysdeps/posix/clock.c           |   1 +
 sysdeps/posix/pathsearch.c      |  93 ++++++++++++++++++
 sysdeps/posix/tempname.c        | 165 ++++++++++----------------------
 sysdeps/unix/sysv/linux/clock.c |   1 +
 time/clock.c                    |   1 +
 10 files changed, 183 insertions(+), 124 deletions(-)
 create mode 100644 stdio-common/pathsearch.c
 create mode 100644 sysdeps/posix/pathsearch.c

Comments

Florian Weimer Oct. 23, 2023, 1:31 p.m. UTC | #1
* Adhemerval Zanella:

> +#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
>  
> +  *r = mix_random_values (v, clock ());
> +  return false;

We shouldn't have fallback to clock in glibc.

Thanks,
Florian
Adhemerval Zanella Netto Oct. 23, 2023, 2:09 p.m. UTC | #2
On 23/10/23 10:31, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> +#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
>>  
>> +  *r = mix_random_values (v, clock ());
>> +  return false;
> 
> We shouldn't have fallback to clock in glibc.

Sounds reasonable, I will update the patch.
diff mbox series

Patch

diff --git a/include/time.h b/include/time.h
index f599eeed4e..94535eb1de 100644
--- a/include/time.h
+++ b/include/time.h
@@ -340,6 +340,8 @@  extern __time64_t __time64 (__time64_t *timer);
 libc_hidden_proto (__time64)
 #endif
 
+libc_hidden_proto (clock);
+
 /* Use in the clock_* functions.  Size of the field representing the
    actual clock ID.  */
 #define CLOCK_IDFIELD_SIZE	3
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index e88a9cea29..154b90f1a6 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -61,6 +61,7 @@  routines := \
   itoa-digits \
   itoa-udigits \
   itowa-digits \
+  pathsearch \
   perror \
   printf \
   printf-prs \
diff --git a/stdio-common/pathsearch.c b/stdio-common/pathsearch.c
new file mode 100644
index 0000000000..264b1cde57
--- /dev/null
+++ b/stdio-common/pathsearch.c
@@ -0,0 +1,30 @@ 
+/* Path search algorithm, for tmpnam, tmpfile, etc.  Generic version.
+   Copyright (C) 2023 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, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* 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)
+
diff --git a/stdio-common/tempname.c b/stdio-common/tempname.c
index 8c660b38c6..443714d071 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/sysdeps/mach/hurd/clock.c b/sysdeps/mach/hurd/clock.c
index 6f510dfebd..649ec3b1e8 100644
--- a/sysdeps/mach/hurd/clock.c
+++ b/sysdeps/mach/hurd/clock.c
@@ -51,3 +51,4 @@  clock (void)
 
   return total;
 }
+libc_hidden_def (clock)
diff --git a/sysdeps/posix/clock.c b/sysdeps/posix/clock.c
index 6aa113f78e..92f90c0245 100644
--- a/sysdeps/posix/clock.c
+++ b/sysdeps/posix/clock.c
@@ -29,3 +29,4 @@  clock (void)
 
   return buf.tms_utime + buf.tms_stime;
 }
+libc_hidden_def (clock)
diff --git a/sysdeps/posix/pathsearch.c b/sysdeps/posix/pathsearch.c
new file mode 100644
index 0000000000..18198e86fc
--- /dev/null
+++ b/sysdeps/posix/pathsearch.c
@@ -0,0 +1,93 @@ 
+/* Path search algorithm, for tmpnam, tmpfile, etc.  POSIX version.
+   Copyright (C) 2023 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, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+/* Return nonzero if DIR is an existent directory.  */
+static bool
+direxists (const char *dir)
+{
+  struct __stat64_t64 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 $TMPDIR,
+   P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
+   for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
+   doesn't exist, none of the searched dirs exists, or there's not
+   enough space in TMPL. */
+int
+__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
+               int try_tmpdir)
+{
+  const char *d;
+  size_t dlen, plen;
+
+  if (!pfx || !pfx[0])
+    {
+      pfx = "file";
+      plen = 4;
+    }
+  else
+    {
+      plen = strlen (pfx);
+      if (plen > 5)
+        plen = 5;
+    }
+
+  if (try_tmpdir)
+    {
+      d = __libc_secure_getenv ("TMPDIR");
+      if (d != NULL && direxists (d))
+        dir = d;
+      else if (dir != NULL && direxists (dir))
+        /* nothing */ ;
+      else
+        dir = NULL;
+    }
+  if (dir == NULL)
+    {
+      if (direxists (P_tmpdir))
+        dir = P_tmpdir;
+      else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
+        dir = "/tmp";
+      else
+        {
+          __set_errno (ENOENT);
+          return -1;
+        }
+    }
+
+  dlen = strlen (dir);
+  while (dlen > 1 && dir[dlen - 1] == '/')
+    dlen--;                     /* remove trailing slashes */
+
+  /* check we have room for "${dir}/${pfx}XXXXXX\0" */
+  if (tmpl_len < dlen + 1 + plen + 6 + 1)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
+  return 0;
+}
diff --git a/sysdeps/posix/tempname.c b/sysdeps/posix/tempname.c
index f24d962288..bf362db6e1 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 +66,56 @@  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)
 
+/* 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;
+  *r = mix_random_values (v, clock ());
+  return false;
 }
-#endif /* _LIBC */
 
 #if _LIBC
 static int try_tempname_len (char *, int, void *, int (*) (char *, void *),
@@ -213,7 +164,7 @@  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
@@ -261,25 +212,17 @@  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);
@@ -299,18 +242,16 @@  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--;
         }
 
diff --git a/sysdeps/unix/sysv/linux/clock.c b/sysdeps/unix/sysv/linux/clock.c
index da005076e9..63c8baec35 100644
--- a/sysdeps/unix/sysv/linux/clock.c
+++ b/sysdeps/unix/sysv/linux/clock.c
@@ -34,3 +34,4 @@  clock (void)
   return (ts.tv_sec * CLOCKS_PER_SEC
 	  + ts.tv_nsec / (1000000000 / CLOCKS_PER_SEC));
 }
+libc_hidden_def (clock)
diff --git a/time/clock.c b/time/clock.c
index 3eb345b8c0..7c86701670 100644
--- a/time/clock.c
+++ b/time/clock.c
@@ -26,5 +26,6 @@  clock (void)
   __set_errno (ENOSYS);
   return (clock_t) -1;
 }
+libc_hidden_def (clock)
 
 stub_warning (clock)