Add timingsafe_bcmp(), for constant-time memory comparison

timingsafe_bcmp() should be used instead of memcmp() or a naive
for-loop, when comparing passwords or secret tokens, to avoid leaking
information about the secret token by timing. This commit just
introduces the function but does not change any existing code to use
it yet.

This has been initially applied as of 09be39112654 in v18 and newer
versions, and will be used in all the stable branches for an upcoming
fix.

Co-authored-by: Jelte Fennema-Nio <github-tech@jeltef.nl>
Discussion: https://www.postgresql.org/message-id/7b86da3b-9356-4e50-aa1b-56570825e234@iki.fi
Security: CVE-2026-6478
Backpatch-through: 14

diff --git a/configure b/configure
index bf6c773b5dd6f1c8cbd643ebf94c0c218290262a..234f476ac6431339d52fa54fb6b8374fbb0da769 100755 (executable)
--- a/configure
+++ b/configure
@@ -15878,6 +15878,16 @@ fi
 cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_STRNLEN $ac_have_decl
 _ACEOF
+ac_fn_c_check_decl "$LINENO" "timingsafe_bcmp" "ac_cv_have_decl_timingsafe_bcmp" "$ac_includes_default"
+if test "x$ac_cv_have_decl_timingsafe_bcmp" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_TIMINGSAFE_BCMP $ac_have_decl
+_ACEOF
 
 
 # We can't use AC_CHECK_FUNCS to detect these functions, because it
@@ -16050,6 +16060,19 @@ esac
 
 fi
 
+ac_fn_c_check_func "$LINENO" "timingsafe_bcmp" "ac_cv_func_timingsafe_bcmp"
+if test "x$ac_cv_func_timingsafe_bcmp" = xyes; then :
+  $as_echo "#define HAVE_TIMINGSAFE_BCMP 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" timingsafe_bcmp.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS timingsafe_bcmp.$ac_objext"
+ ;;
+esac
+
+fi
+
 
 
 ac_fn_c_check_func "$LINENO" "pthread_barrier_wait" "ac_cv_func_pthread_barrier_wait"

diff --git a/configure.ac b/configure.ac
index 7bfdc3ec82c1669179778600929a89a71854a90d..fd6ae577577e93c4a4bcafe714394842b13c625c 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1796,7 +1796,7 @@ AC_CHECK_DECLS(posix_fadvise, [], [], [#include <fcntl.h>])
 ]) # fi
 
 AC_CHECK_DECLS(fdatasync, [], [], [#include <unistd.h>])
-AC_CHECK_DECLS([strlcat, strlcpy, strnlen])
+AC_CHECK_DECLS([strlcat, strlcpy, strnlen, timingsafe_bcmp])
 
 # We can't use AC_CHECK_FUNCS to detect these functions, because it
 # won't handle deployment target restrictions on macOS
@@ -1818,6 +1818,7 @@ AC_REPLACE_FUNCS(m4_normalize([
        strlcat
        strlcpy
        strnlen
+       timingsafe_bcmp
 ]))
 
 AC_REPLACE_FUNCS(pthread_barrier_wait)

diff --git a/meson.build b/meson.build
index 73e30a170907fd8f4e55bf7d050ce357e8ae5a6b..fc3236839c7707329292468b3a5d76dea49ddd6b 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -2484,6 +2484,7 @@ decl_checks = [
   ['strlcat', 'string.h'],
   ['strlcpy', 'string.h'],
   ['strnlen', 'string.h'],
+  ['timingsafe_bcmp',  'string.h'],
 ]
 
 # Need to check for function declarations for these functions, because
@@ -2772,6 +2773,7 @@ func_checks = [
   ['strsignal'],
   ['sync_file_range'],
   ['syncfs'],
+  ['timingsafe_bcmp'],
   ['uselocale'],
   ['wcstombs_l'],
 ]

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index ee75c7da5ae37d8da44c8508aee3f24bd43267a8..5bd30dd3949d0fa8cfe2dcd4af1010551761b254 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -135,6 +135,10 @@
    don't. */
 #undef HAVE_DECL_STRNLEN
 
+/* Define to 1 if you have the declaration of `timingsafe_bcmp', and to 0 if
+   you don't. */
+#undef HAVE_DECL_TIMINGSAFE_BCMP
+
 /* Define to 1 if you have the <editline/history.h> header file. */
 #undef HAVE_EDITLINE_HISTORY_H
 
@@ -467,6 +471,9 @@
 /* Define to 1 if you have the <termios.h> header file. */
 #undef HAVE_TERMIOS_H
 
+/* Define to 1 if you have the `timingsafe_bcmp' function. */
+#undef HAVE_TIMINGSAFE_BCMP
+
 /* Define to 1 if your compiler understands `typeof' or something similar. */
 #undef HAVE_TYPEOF
 

diff --git a/src/include/port.h b/src/include/port.h
index 6796533ac9014b4c2caf9c604d848b820ba6e92c..a90d0cf32f3bf83ec8011597f83b587f355c11bc 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -465,6 +465,10 @@ extern bool pg_get_user_name(uid_t user_id, char *buffer, size_t buflen);
 extern bool pg_get_user_home_dir(uid_t user_id, char *buffer, size_t buflen);
 #endif
 
+#if !HAVE_DECL_TIMINGSAFE_BCMP
+extern int     timingsafe_bcmp(const void *b1, const void *b2, size_t len);
+#endif
+
 /*
  * Callers should use the qsort() macro defined below instead of calling
  * pg_qsort() directly.

diff --git a/src/port/meson.build b/src/port/meson.build
index 90f837248defae1ad6b1f1f91fd203a18be4782b..565324af595587c3da77d6f21cd87325356d9f56 100644 (file)
--- a/src/port/meson.build
+++ b/src/port/meson.build
@@ -70,6 +70,7 @@ replace_funcs_neg = [
   ['strlcat'],
   ['strlcpy'],
   ['strnlen'],
+  ['timingsafe_bcmp'],
 ]
 
 if host_system != 'windows'

diff --git a/src/port/timingsafe_bcmp.c b/src/port/timingsafe_bcmp.c
new file mode 100644 (file)
index 0000000..288865f
--- /dev/null
+++ b/src/port/timingsafe_bcmp.c
@@ -0,0 +1,43 @@
+/*
+ * src/port/timingsafe_bcmp.c
+ *
+ *     $OpenBSD: timingsafe_bcmp.c,v 1.3 2015/08/31 02:53:57 guenther Exp $
+ */
+
+/*
+ * Copyright (c) 2010 Damien Miller.  All rights reserved.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "c.h"
+
+#ifdef USE_SSL
+#include <openssl/crypto.h>
+#endif
+
+int
+timingsafe_bcmp(const void *b1, const void *b2, size_t n)
+{
+#ifdef USE_SSL
+       return CRYPTO_memcmp(b1, b2, n);
+#else
+       const unsigned char *p1 = b1,
+                          *p2 = b2;
+       int                     ret = 0;
+
+       for (; n > 0; n--)
+               ret |= *p1++ ^ *p2++;
+       return (ret != 0);
+#endif
+}