krb5 commit: Avoid small read overrun in UTF8 normalization

[ghudson at mit.edu]

https://github.com/krb5/krb5/commit/fb9cf8cfbf8da0d160cb61250b952f2b8e5484f4
commit fb9cf8cfbf8da0d160cb61250b952f2b8e5484f4
Author: Greg Hudson <ghudson at mit.edu>
Date:   Wed Oct 12 00:27:17 2022 -0400

    Avoid small read overrun in UTF8 normalization
    
    In krb5int_utf8_normalize(), check the length of the current character
    against the buffer length before reading more than one byte.  Credit
    to OSS-Fuzz for discovering the overrun.
    
    ticket: 9072 (new)

 src/lib/krb5/unicode/ucstr.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/lib/krb5/unicode/ucstr.c b/src/lib/krb5/unicode/ucstr.c
index 21030bf25..e3ed9bc64 100644
--- a/src/lib/krb5/unicode/ucstr.c
+++ b/src/lib/krb5/unicode/ucstr.c
@@ -199,6 +199,12 @@ krb5int_utf8_normalize(
 	/* s[i] is non-ascii */
 	/* convert everything up to next ascii to ucs-4 */
 	while (i < len) {
+	    /* KRB5_UTF8_CHARLEN only looks at the first byte; use it to guard
+	     * against small read overruns. */
+	    if (KRB5_UTF8_CHARLEN(s + i) > len - i) {
+		retval = KRB5_ERR_INVALID_UTF8;
+		goto cleanup;
+	    }
 	    clen = KRB5_UTF8_CHARLEN2(s + i, clen);
 	    if (clen == 0) {
 		retval = KRB5_ERR_INVALID_UTF8;