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 8e31a68eb477743fcc1beb950e17e1e1c4194bbd..915c98a2d66b9b527fcf857ec7c512ec87aad848 100755 (executable)
--- a/configure
+++ b/configure
@@ -16974,6 +16974,16 @@ 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
@@ -17326,6 +17336,19 @@ 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 a7a8cd48dc64c2c6914a230aba0fee848c4beacf..3fe1f8fc37b8b59d68a45b42446ac9b8c288bfb5 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1917,7 +1917,7 @@ 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
@@ -1967,6 +1967,7 @@ AC_REPLACE_FUNCS(m4_normalize([
        strlcpy
        strnlen
        strtof
+       timingsafe_bcmp
 ]))
 
 if test "$enable_thread_safety" = yes; then

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 9f1815249271528298013dc2c1e7d94630df696f..ea9adec2b08b676834cf5fbfa0c8a311f783c053 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -178,6 +178,10 @@
    don't. */
 #undef HAVE_DECL_STRTOULL
 
+/* 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 `dlopen' function. */
 #undef HAVE_DLOPEN
 
@@ -669,6 +673,9 @@
 /* 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 3f67ab18607d85fa19dd90f7b5155040160abdbb..65dfa54982c153b5b4ddf3e18dc0577d3ab9185d 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -519,6 +519,10 @@ 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/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 3cbc8a83984feef354bced750ac6054f0fe66795..e0108a4322559f2675c4557e065c0763e52c9eef 100644 (file)
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -106,7 +106,7 @@ sub mkvcbuild
          pread.c preadv.c pwrite.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 win32env.c win32error.c win32fseek.c win32ntdll.c
          win32security.c win32setlocale.c win32stat.c);
 

diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index c9bbba480b509454904fe0f08ffe5709dbac62aa..3a6159edcd6b03fac977c5822105e566c270d2b3 100644 (file)
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -253,6 +253,7 @@ sub GenerateFiles
                HAVE_DECL_STRNLEN                           => 1,
                HAVE_DECL_STRTOLL                           => 1,
                HAVE_DECL_STRTOULL                          => 1,
+               HAVE_DECL_TIMINGSAFE_BCMP                   => 0,
                HAVE_DLOPEN                                 => undef,
                HAVE_EDITLINE_HISTORY_H                     => undef,
                HAVE_EDITLINE_READLINE_H                    => undef,
@@ -415,6 +416,7 @@ sub GenerateFiles
                HAVE_SYS_UIO_H                           => undef,
                HAVE_SYS_UN_H                            => undef,
                HAVE_TERMIOS_H                           => undef,
+               HAVE_TIMINGSAFE_BCMP                     => undef,
                HAVE_TYPEOF                              => undef,
                HAVE_UCRED_H                             => undef,
                HAVE_UINT64                              => undef,