rgw: sanitize newlines in s3 CORSConfiguration's ExposeHeader

the values in the <ExposeHeader> element are sent back to clients in a
Access-Control-Expose-Headers response header. if the values are allowed
to have newlines in them, they can be used to inject arbitrary response
headers

this issue only affects s3, which gets these values from an xml document

in swift, they're given in the request header
X-Container-Meta-Access-Control-Expose-Headers, so the value itself
cannot contain newlines

Signed-off-by: Casey Bodley <cbodley@redhat.com>
Reported-by: Adam Mohammed <amohammed@linode.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/rgw/rgw_cors.cc b/src/rgw/rgw_cors.cc
index 422767f34eb..94d08f7ae3b 100644
--- a/src/rgw/rgw_cors.cc
+++ b/src/rgw/rgw_cors.cc
@@ -144,11 +144,12 @@ bool RGWCORSRule::is_header_allowed(const char *h, size_t len) {
 
 void RGWCORSRule::format_exp_headers(string& s) {
   s = "";
-  for(list<string>::iterator it = exposable_hdrs.begin();
-      it != exposable_hdrs.end(); ++it) {
-      if (s.length() > 0)
-        s.append(",");
-      s.append((*it));
+  for (const auto& header : exposable_hdrs) {
+    if (s.length() > 0)
+      s.append(",");
+    // these values are sent to clients in a 'Access-Control-Expose-Headers'
+    // response header, so we escape '\n' to avoid header injection
+    boost::replace_all_copy(std::back_inserter(s), header, "\n", "\\n");
   }
 }