Backport of:

From 625924941cbd684c2a6b10d18aa6920a27c31db3 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Tue, 3 May 2022 09:24:56 +0200
Subject: [PATCH] nss: return error if seemingly stuck in a cert loop
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CVE-2022-27781

Reported-by: Florian Kohnhäuser
Bug: https://curl.se/docs/CVE-2022-27781.html
---
 lib/vtls/nss.c | 8 ++++++++
 1 file changed, 8 insertions(+)

--- a/lib/vtls/nss.c
+++ b/lib/vtls/nss.c
@@ -949,6 +949,9 @@ static void display_cert_info(struct Cur
   PR_Free(common_name);
 }
 
+/* A number of certs that will never occur in a real server handshake */
+#define TOO_MANY_CERTS 300
+
 static CURLcode display_conn_info(struct connectdata *conn, PRFileDesc *sock)
 {
   CURLcode result = CURLE_OK;
@@ -985,6 +988,11 @@ static CURLcode display_conn_info(struct
         cert2 = CERT_FindCertIssuer(cert, now, certUsageSSLCA);
         while(cert2) {
           i++;
+          if(i >= TOO_MANY_CERTS) {
+            CERT_DestroyCertificate(cert2);
+            failf(conn->data, "certificate loop");
+            return CURLE_SSL_CERTPROBLEM;
+          }
           if(cert2->isRoot) {
             CERT_DestroyCertificate(cert2);
             break;
