Strengthen APOP a bit (validate RFC-822 syntax) in order to fend off

Leurent-style MITM attacks which are based on MD5 and APOP weaknesses.

svn path=/branches/BRANCH_6-3/; revision=5057

1 files changed, 140 insertions, 0 deletions

diff --git a/rfc822valid.c b/rfc822valid.c
new file mode 100644
index 00000000..0fabe1ef
--- /dev/null
+++ b/rfc822valid.c
@@ -0,0 +1,140 @@
+/* rfc822valid.c -- validators for RFC-822 syntax
+ * (C) Copyright 2007 Matthias Andree <matthias.andree@gmx.de>
+ * GNU General Public License v2 */
+
+/* This works only on ASCII-based computers. */
+
+#include "fetchmail.h"
+#include <string.h>
+
+/* CHAR except specials, SPACE, CTLs */
+static const char *atomchar = "!#$%&'*+-/0123456789=?ABCDEFGHIJKLMNOPQRSTUVWXYZ^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+static int quotedpair(unsigned char const **x) {
+    if (**x != '\\') return 0;
+    ++ *x;
+    if ((int)* *x > 127 || * *x == '\0')
+	/* XXX FIXME: 0 is a legal CHAR, so the == '\0' is sort of bogus
+	 * above, but fetchmail does not currently deal with NUL inputs
+	 * so we don't need to make the distinction between
+	 * end-of-string and quoted NUL. */
+	return 0;
+    ++ *x;
+    return 1;
+}
+
+
+static int quotedstring(unsigned char const **x) {
+    if (* *x != '"') return 0;
+    ++ *x;
+    for(;;) {
+	switch (* *x) {
+	    case '"':
+		++ *x;
+		return 1;
+	    case '\\':
+		if (quotedpair(x) == 0) return 0;
+		continue;
+	    case '\r':
+	    case '\0':
+		return 0;
+	}
+	if ((int)* *x >= 128) {
+	    return 0;
+	}
+	++ *x;
+    }
+}
+
+static int atom(unsigned char const **x) {
+    /* atom */
+    if (strchr(atomchar, (const char)**x)) {
+	*x += strspn((const char *)*x, atomchar);
+	return 1;
+    }
+    /* invalid character */
+    return 0;
+}
+
+static int word(unsigned char const **x) {
+    if (**x == '"')
+	return quotedstring(x);
+    return atom(x);
+}
+
+static int domain_literal(unsigned char const **x) {
+    if (**x != '[') return 0;
+    ++ *x;
+    for(;;) {
+	switch (* *x) {
+	    case '\0':
+	    case '\r':
+	    case '[':
+		return 0;
+	    case ']':
+		++ *x;
+		return 1;
+	    case '\\':
+		if (quotedpair(x) == 0) return 0;
+		continue;
+	}
+	if ((int)* *x > 127) return 0;
+	++ *x;
+    }
+}
+
+static int subdomain(unsigned char const **x) {
+    if (* *x == '[') return domain_literal(x);
+    return atom(x);
+}
+
+int rfc822_valid_msgid(const unsigned char *x) {
+    /* expect "<" */
+    if (*x != '<') return 0;
+    ++ x;
+
+    /* expect local-part = word *("." word)
+     * where
+     * word = atom/quoted-string
+     * atom = 1*ATOMCHAR
+     * quoted-string = <"> *(qtext/quoted-pair) <">
+     * qtext = CHAR except ", \, CR
+     * quoted-pair = "\" CHAR
+     */
+    for(;;) {
+	if (word(&x) == 0) return 0;
+	if (*x == '.') { ++x; continue; }
+	if (*x == '@') break;
+	return 0;
+    }
+
+    /* expect "@" */
+    if (*x != '@') return 0;
+    ++ x;
+
+    /* expect domain = sub-domain *("." sub-domain)
+     * sub-domain = domain-ref/domain-literal
+     * domain-ref = atom
+     * domain-literal = "[" *(dtext/quoted-pair) "]" */
+    for(;;) {
+	if (subdomain(&x) == 0) return 0;
+	if (*x == '.') { ++x; continue; }
+	if (*x == '>') break;
+	return 0;
+    }
+
+    if (*x != '>') return 0;
+    return 1;
+}
+
+#ifdef TEST
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+    int i;
+    for (i = 1; i < argc; i++) {
+	printf("%s: %s\n", argv[i], rfc822_valid_msgid((unsigned char *)argv[i]) ? "OK" : "INVALID");
+    }
+    return 0;
+}
+#endif