Add fmtcheck(), a function for checking consistency of format string

arguments where the format string is obtained from user data, or
otherwise difficult to verify statically.

Example usage:

printf(fmtcheck(user_format, standard_format), arg1, arg2);

checks the format string user_format for consistency (same number/order/
type of format operators) with standard_format.  If they differ,
standard_format is used instead to avoid potential crashes or security
violations.

Obtained from:  NetBSD
Reviewed by:    -arch

3 files changed, 355 insertions, 2 deletions

diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index eba9beb..96ec3b9 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -9,7 +9,7 @@ SRCS+=  __xuname.c _pthread_stubs.c _rand48.c _spinlock_stub.c _thread_init.c \
 	clock.c closedir.c confstr.c \
 	crypt.c ctermid.c daemon.c devname.c dirname.c disklabel.c \
 	dlfcn.c drand48.c erand48.c err.c errlst.c \
-	exec.c fnmatch.c fstab.c ftok.c fts.c getbootfile.c getbsize.c \
+	exec.c fmtcheck.c fnmatch.c fstab.c ftok.c fts.c getbootfile.c getbsize.c \
 	getcap.c getcwd.c getdomainname.c getgrent.c getgrouplist.c \
 	gethostname.c getloadavg.c getlogin.c getmntinfo.c getnetgrent.c \
 	getobjformat.c getosreldate.c getpagesize.c \
@@ -38,7 +38,7 @@ MAN+=	alarm.3 arc4random.3 clock.3 \
 	basename.3 \
 	confstr.3 ctermid.3 daemon.3 \
 	devname.3 directory.3 dirname.3 dladdr.3 dllockinit.3 dlopen.3 \
-	err.3 exec.3 fnmatch.3 frexp.3 ftok.3 fts.3 \
+	err.3 exec.3 fmtcheck.3 fnmatch.3 frexp.3 ftok.3 fts.3 \
 	getbootfile.3 getbsize.3 getcap.3 getcwd.3 \
 	getdiskbyname.3 getdomainname.3 getfsent.3 \
 	getgrent.3 getgrouplist.3 gethostname.3 getloadavg.3 \
diff --git a/lib/libc/gen/fmtcheck.3 b/lib/libc/gen/fmtcheck.3
new file mode 100644
index 0000000..d52ea48
--- /dev/null
+++ b/lib/libc/gen/fmtcheck.3
@@ -0,0 +1,100 @@
+.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
+.\" All rights reserved.
+.\"
+.\" This file was contributed to The NetBSD Foundation by Allen Briggs.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"        This product includes software developed by the NetBSD
+.\"        Foundation, Inc. and its contributors.
+.\" 4. Neither the name of The NetBSD Foundation nor the names of its
+.\"    contributors may be used to endorse or promote products derived
+.\"    from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.Dd October 17, 2000
+.Os
+.Dt FMTCHECK 3
+.Sh NAME
+.Nm fmtcheck
+.Nd sanitizes user-supplied printf(3)-style format string
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.Fd #include <stdio.h>
+.Ft const char *
+.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default"
+.Sh DESCRIPTION
+The
+.Nm
+function scans
+.Fa fmt_suspect
+and
+.Fa fmt_default
+to determine if
+.Fa fmt_suspect
+will consume the same argument types as
+.Fa fmt_default
+and to ensure that
+.Fa fmt_suspect
+is a valid format string.
+.Pp
+The
+.Xr printf 3
+family of functions can not verify the types of arguments that they are
+passed at run-time.  In some cases, like
+.Xr catgets 3 ,
+it is useful or necessary to use a user-supplied format string with no
+guarantee that the format string matches the specified parameters.
+.Pp
+The
+.Nm
+function was designed to be used in these cases, as in:
+.Bd -literal -offset indent
+printf(fmtcheck(user_format, standard_format), arg1, arg2);
+.Ed
+.Pp
+In the check, field widths, fillers, precisions, etc. are ignored (unless
+the field width or precision is an asterisk
+.Ql *
+instead of a digit string).  Also, any text other than the format specifiers
+is completely ignored.
+.Pp
+Note that the formats may be quite different as long as they accept the
+same parameters.  For example, ".Dq %p %o %30s %#llx %-10.*e %n" is
+compatible with "This number %lu %d%% and string %s has %qd numbers
+and %.*g floats (%n)."  However, "%o" is not equivalent to "%lx" because
+the first requires an integer and the second requires a long.
+.Sh RETURN VALUES
+If
+.Fa fmt_suspect
+is a valid format and consumes the same argument types as
+.Fa fmt_default ,
+then the
+.Nm
+function will return
+.Fa fmt_suspect .
+Otherwise, it will return
+.Fa fmt_default .
+.Sh SEE ALSO
+.Xr printf 3
diff --git a/lib/libc/gen/fmtcheck.c b/lib/libc/gen/fmtcheck.c
new file mode 100644
index 0000000..7cc8cff
--- /dev/null
+++ b/lib/libc/gen/fmtcheck.c
@@ -0,0 +1,253 @@
+/*	$FreeBSD$	*/
+/*	$NetBSD: fmtcheck.c,v 1.2 2000/11/01 01:17:20 briggs Exp $	*/
+
+/*-
+ * Copyright (c) 2000 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code was contributed to The NetBSD Foundation by Allen Briggs.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *        This product includes software developed by the NetBSD
+ *        Foundation, Inc. and its contributors.
+ * 4. Neither the name of The NetBSD Foundation nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+#ifndef lint
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include "namespace.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#ifdef __weak_alias
+__weak_alias(fmtcheck,__fmtcheck)
+#endif
+
+enum __e_fmtcheck_types {
+	FMTCHECK_START,
+	FMTCHECK_SHORT,
+	FMTCHECK_INT,
+	FMTCHECK_LONG,
+	FMTCHECK_QUAD,
+	FMTCHECK_SHORTPOINTER,
+	FMTCHECK_INTPOINTER,
+	FMTCHECK_LONGPOINTER,
+	FMTCHECK_QUADPOINTER,
+	FMTCHECK_DOUBLE,
+	FMTCHECK_LONGDOUBLE,
+	FMTCHECK_STRING,
+	FMTCHECK_WIDTH,
+	FMTCHECK_PRECISION,
+	FMTCHECK_DONE,
+	FMTCHECK_UNKNOWN
+};
+typedef enum __e_fmtcheck_types EFT;
+
+#define RETURN(pf,f,r) do { \
+			*(pf) = (f); \
+			return r; \
+		       } /*NOTREACHED*/ /*CONSTCOND*/ while (0)
+
+static EFT
+get_next_format_from_precision(const char **pf)
+{
+	int		sh, lg, quad, longdouble;
+	const char	*f;
+
+	sh = lg = quad = longdouble = 0;
+
+	f = *pf;
+	switch (*f) {
+	case 'h':
+		f++;
+		sh = 1;
+		break;
+	case 'l':
+		f++;
+		if (!*f) RETURN(pf,f,FMTCHECK_UNKNOWN);
+		if (*f == 'l') {
+			f++;
+			quad = 1;
+		} else {
+			lg = 1;
+		}
+		break;
+	case 'q':
+		f++;
+		quad = 1;
+		break;
+	case 'L':
+		f++;
+		longdouble = 1;
+		break;
+	default:
+		break;
+	}
+	if (!*f) RETURN(pf,f,FMTCHECK_UNKNOWN);
+	if (strchr("diouxX", *f)) {
+		if (longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		if (lg)
+			RETURN(pf,f,FMTCHECK_LONG);
+		if (quad)
+			RETURN(pf,f,FMTCHECK_QUAD);
+		RETURN(pf,f,FMTCHECK_INT);
+	}
+	if (*f == 'n') {
+		if (longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		if (sh)
+			RETURN(pf,f,FMTCHECK_SHORTPOINTER);
+		if (lg)
+			RETURN(pf,f,FMTCHECK_LONGPOINTER);
+		if (quad)
+			RETURN(pf,f,FMTCHECK_QUADPOINTER);
+		RETURN(pf,f,FMTCHECK_INTPOINTER);
+	}
+	if (strchr("DOU", *f)) {
+		if (sh + lg + quad + longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		RETURN(pf,f,FMTCHECK_LONG);
+	}
+	if (strchr("eEfg", *f)) {
+		if (longdouble)
+			RETURN(pf,f,FMTCHECK_LONGDOUBLE);
+		if (sh + lg + quad)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		RETURN(pf,f,FMTCHECK_DOUBLE);
+	}
+	if (*f == 'c') {
+		if (sh + lg + quad + longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		RETURN(pf,f,FMTCHECK_INT);
+	}
+	if (*f == 's') {
+		if (sh + lg + quad + longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		RETURN(pf,f,FMTCHECK_STRING);
+	}
+	if (*f == 'p') {
+		if (sh + lg + quad + longdouble)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		RETURN(pf,f,FMTCHECK_LONG);
+	}
+	RETURN(pf,f,FMTCHECK_UNKNOWN);
+	/*NOTREACHED*/
+}
+
+static EFT
+get_next_format_from_width(const char **pf)
+{
+	const char	*f;
+
+	f = *pf;
+	if (*f == '.') {
+		f++;
+		if (*f == '*') {
+			RETURN(pf,f,FMTCHECK_PRECISION);
+		}
+		/* eat any precision (empty is allowed) */
+		while (isdigit(*f)) f++;
+		if (!*f) RETURN(pf,f,FMTCHECK_UNKNOWN);
+	}
+	RETURN(pf,f,get_next_format_from_precision(pf));
+	/*NOTREACHED*/
+}
+
+static EFT
+get_next_format(const char **pf, EFT eft)
+{
+	int		infmt;
+	const char	*f;
+
+	if (eft == FMTCHECK_WIDTH) {
+		(*pf)++;
+		return get_next_format_from_width(pf);
+	} else if (eft == FMTCHECK_PRECISION) {
+		(*pf)++;
+		return get_next_format_from_precision(pf);
+	}
+
+	f = *pf;
+	infmt = 0;
+	while (!infmt) {
+		f = strchr(f, '%');
+		if (f == NULL)
+			RETURN(pf,f,FMTCHECK_DONE);
+		f++;
+		if (!*f)
+			RETURN(pf,f,FMTCHECK_UNKNOWN);
+		if (*f != '%')
+			infmt = 1;
+		else
+			f++;
+	}
+
+	/* Eat any of the flags */
+	while (*f && (strchr("#0- +", *f)))
+		f++;
+
+	if (*f == '*') {
+		RETURN(pf,f,FMTCHECK_WIDTH);
+	}
+	/* eat any width */
+	while (isdigit(*f)) f++;
+	if (!*f) {
+		RETURN(pf,f,FMTCHECK_UNKNOWN);
+	}
+
+	RETURN(pf,f,get_next_format_from_width(pf));
+	/*NOTREACHED*/
+}
+
+__const char *
+fmtcheck(const char *f1, const char *f2)
+{
+	const char	*f1p, *f2p;
+	EFT		f1t, f2t;
+
+	if (!f1) return f2;
+	
+	f1p = f1;
+	f1t = FMTCHECK_START;
+	f2p = f2;
+	f2t = FMTCHECK_START;
+	while ((f1t = get_next_format(&f1p, f1t)) != FMTCHECK_DONE) {
+		if (f1t == FMTCHECK_UNKNOWN)
+			return f2;
+		f2t = get_next_format(&f2p, f2t);
+		if (f1t != f2t)
+			return f2;
+	}
+	return f1;
+}