imap_sasl_callback() protocol check is incomplete

Stephen Gildea <[email protected]> Sun, 29 Jun 2025 11:29:55 -0700

Newsgroups	gmane.mail.nmh.devel
Message-ID	<[email protected]>

When function 'imap_sasl_callback' reads a response from the server, it
appears that it intends to check that the first 2 characters are "+ ".

Actually, the code checks this only in the case of a blank response,
because the check is limited by testing if "len == 2".

This patch replaces the whole multi-clause test with a call to
has_prefix_len(), making the code both correct and more readable.

sasl_callback_read_protocol_check.diff (text/x-diff, 445 B)

diff --git a/uip/imaptest.c b/uip/imaptest.c
index 8167a7ff..5d891420 100644
--- a/uip/imaptest.c
+++ b/uip/imaptest.c
@@ -644,7 +644,7 @@ imap_sasl_callback(enum sasl_message_type mtype, unsigned const char *indata,
 	if (line == NULL)
 	    return NOTOK;
 
-	if (len < 2 || (len == 2 && strcmp(line, "+ ") != 0)) {
+	if (!has_prefix_len(line, len, "+ ")) {
 	    netsec_err(errstr, "Invalid format for SASL response");
 	    return NOTOK;
 	}