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 77f8372cb7e867bd05b9285821b98f23f2fbf4b0..988ed07cab59139cfff83a6938430e2104a5fd19 100755 (executable)
--- a/configure
+++ b/configure
@@ -16643,6 +16643,16 @@ 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
@@ -17021,6 +17031,19 @@ 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 b84fa574860b2d3d31914f7dc9d1dc3baeb31960..f8d9a8cc0505b0966d2cc2e15091213f65de58a2 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
@@ -1894,6 +1894,7 @@ 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 cdb98885a298a8c5720e134ef819e338a3f61819..528e09c1601bfdac463553c6ef42ea356e62e66d 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -183,6 +183,10 @@
    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 a8ec28b1028f289674ee66df2ff4f58052ebc1ed..db53decbbef73a3da15bfd7f2259afc233ee326c 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -534,6 +534,10 @@ extern int pqGethostbyname(const char *name,
                                                        struct hostent **result,
                                                        int *herrno);
 
+#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 43880a0a34c1e03f34277ce403ed9067eb02e93a..5db388bdbac1813f5d9846d750397cf8e6e1da58 100644 (file)
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -111,7 +111,7 @@ 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 thread.c
+         strerror.c tar.c thread.c timingsafe_bcmp.c
          win32common.c win32env.c win32error.c win32ntdll.c win32fseek.c win32security.c
          win32setlocale.c win32stat.c);
 

diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index e1870b8b1fa636b077358901e9a840bc5eef5124..65e7992c21f57273426ab171fd3dba246e1266be 100644 (file)
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -255,6 +255,7 @@ 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,