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 b0308a2b9e70e4b7ba74ef488027a23724f8a059..2eca3122a03b8e8d75826f6e3dc994eb477588c7 100755 (executable)
--- a/configure
+++ b/configure
@@ -16321,6 +16321,16 @@ 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_REPLACE_FUNCS to replace these functions, because it
@@ -16513,6 +16523,19 @@ 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
+
 
 
 if test "$enable_thread_safety" = yes; then

diff --git a/configure.ac b/configure.ac
index 9eefefd6804ebea6277d67ca4949a38aeccadfc4..c4cd6fd1c0f4dc02f4ef16ccc893f9fbad3c892d 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1842,7 +1842,7 @@ 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_REPLACE_FUNCS to replace these functions, because it
 # won't handle deployment target restrictions on macOS
@@ -1864,6 +1864,7 @@ AC_REPLACE_FUNCS(m4_normalize([
        strlcat
        strlcpy
        strnlen
+       timingsafe_bcmp
 ]))
 
 if test "$enable_thread_safety" = yes; then

diff --git a/meson.build b/meson.build
index 517f44d107cab90d8a1feda11867f01b7c8b3085..718132cd73895c3b943af23508c5198fce234382 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -2341,6 +2341,7 @@ 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
@@ -2630,6 +2631,7 @@ 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 d06c49a894200cdca7feeeda0abe5352e72cfe52..f6355cc923efefc9156f23dfaacd77b5463eae79 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -148,6 +148,10 @@
    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
 
@@ -483,6 +487,9 @@
 /* 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 2b2ea07ce5e6f570cfcf5063e7333d13beea0743..3e277d7e308ec371f91efdab954dc0685cb78d21 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
+
 extern void pg_qsort(void *base, size_t nel, size_t elsize,
                                         int (*cmp) (const void *, const void *));
 extern int     pg_qsort_strcmp(const void *a, const void *b);

diff --git a/src/port/meson.build b/src/port/meson.build
index 825bd4d1cb2e1bf9227cd6a0a67386ecd1a1d107..2fefd19068d8d0812ccb14b7872f4dee32e4b54d 100644 (file)
--- a/src/port/meson.build
+++ b/src/port/meson.build
@@ -72,6 +72,7 @@ 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
+}

diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index e224f8d748006b735839846417b8173c39516bd5..ce0e258851268c7f4e9899612b5dbb7d97747ff7 100644 (file)
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -107,7 +107,7 @@ sub mkvcbuild
          preadv.c pwritev.c pg_bitutils.c
          pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
          pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c
-         strerror.c tar.c
+         strerror.c tar.c timingsafe_bcmp.c
          win32common.c
          win32dlopen.c
          win32env.c win32error.c

diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index c0ba9076b31192313d814119bc3c49f5dffcc341..ea440c3453d2e704dc46e9951be59b8a6a636daf 100644 (file)
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -246,6 +246,7 @@ sub GenerateFiles
                HAVE_DECL_STRLCAT => 0,
                HAVE_DECL_STRLCPY => 0,
                HAVE_DECL_STRNLEN => 1,
+               HAVE_DECL_TIMINGSAFE_BCMP => 0,
                HAVE_EDITLINE_HISTORY_H => undef,
                HAVE_EDITLINE_READLINE_H => undef,
                HAVE_EXECINFO_H => undef,
@@ -356,6 +357,7 @@ sub GenerateFiles
                HAVE_SYS_TYPES_H => 1,
                HAVE_SYS_UCRED_H => undef,
                HAVE_TERMIOS_H => undef,
+               HAVE_TIMINGSAFE_BCMP => undef,
                HAVE_TYPEOF => undef,
                HAVE_UCRED_H => undef,
                HAVE_UINT64 => undef,