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From 13363ab0eb3f5a3223571d073888816bd3e650f9 Mon Sep 17 00:00:00 2001
From: Changqing Li <changqing.li@windriver.com>
Date: Tue, 14 Sep 2021 13:49:11 +0800
Subject: [PATCH 1/2] ares_expand_name() should escape more characters
RFC1035 5.1 specifies some reserved characters and escaping sequences
that are allowed to be specified. Expand the list of reserved characters
and also escape non-printable characters using the \DDD format as
specified in the RFC.
Bug Reported By: philipp.jeitner@sit.fraunhofer.de
Fix By: Brad House (@bradh352)
Upstream-Status: Backport [https://github.com/c-ares/c-ares/commit/362f91d807d293791008cdb7616d40f7784ece83]
CVE: CVE-2021-3672
Signed-off-by: Changqing Li <changqing.li@windriver.com>
---
ares_expand_name.c | 41 ++++++++++++++++++++++++++++++++++++++---
1 file changed, 38 insertions(+), 3 deletions(-)
diff --git a/ares_expand_name.c b/ares_expand_name.c
index 3a38e67..8604543 100644
--- a/ares_expand_name.c
+++ b/ares_expand_name.c
@@ -38,6 +38,26 @@
static int name_length(const unsigned char *encoded, const unsigned char *abuf,
int alen);
+/* Reserved characters for names that need to be escaped */
+static int is_reservedch(int ch)
+{
+ switch (ch) {
+ case '"':
+ case '.':
+ case ';':
+ case '\\':
+ case '(':
+ case ')':
+ case '@':
+ case '$':
+ return 1;
+ default:
+ break;
+ }
+
+ return 0;
+}
+
/* Expand an RFC1035-encoded domain name given by encoded. The
* containing message is given by abuf and alen. The result given by
* *s, which is set to a NUL-terminated allocated buffer. *enclen is
@@ -117,9 +137,18 @@ int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
p++;
while (len--)
{
- if (*p == '.' || *p == '\\')
+ if (!isprint(*p)) {
+ /* Output as \DDD for consistency with RFC1035 5.1 */
+ *q++ = '\\';
+ *q++ = '0' + *p / 100;
+ *q++ = '0' + (*p % 100) / 10;
+ *q++ = '0' + (*p % 10);
+ } else if (is_reservedch(*p)) {
*q++ = '\\';
- *q++ = *p;
+ *q++ = *p;
+ } else {
+ *q++ = *p;
+ }
p++;
}
*q++ = '.';
@@ -177,7 +206,13 @@ static int name_length(const unsigned char *encoded, const unsigned char *abuf,
encoded++;
while (offset--)
{
- n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
+ if (!isprint(*encoded)) {
+ n += 4;
+ } else if (is_reservedch(*encoded)) {
+ n += 2;
+ } else {
+ n += 1;
+ }
encoded++;
}
n++;
--
2.17.1
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