Handle set_alpn_protos inputs better.

It's possible to set an invalid protocol list that will be sent in a
ClientHello. This validates the inputs to make sure this does not
happen.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14679)

1 files changed, 43 insertions, 6 deletions

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index 58f8f3c14c..5501ecdb58 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -2829,6 +2829,19 @@ void SSL_CTX_set_npn_select_cb(SSL_CTX *ctx,
 }
 #endif
 
+static int alpn_value_ok(const unsigned char *protos, unsigned int protos_len)
+{
+    unsigned int idx;
+
+    if (protos_len < 2 || protos == NULL)
+        return 0;
+
+    for (idx = 0; idx < protos_len; idx += protos[idx] + 1) {
+        if (protos[idx] == 0)
+            return 0;
+    }
+    return idx == protos_len;
+}
 /*
  * SSL_CTX_set_alpn_protos sets the ALPN protocol list on |ctx| to |protos|.
  * |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
@@ -2837,13 +2850,25 @@ void SSL_CTX_set_npn_select_cb(SSL_CTX *ctx,
 int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const unsigned char *protos,
                             unsigned int protos_len)
 {
-    OPENSSL_free(ctx->ext.alpn);
-    ctx->ext.alpn = OPENSSL_memdup(protos, protos_len);
-    if (ctx->ext.alpn == NULL) {
+    unsigned char *alpn;
+
+    if (protos_len == 0 || protos == NULL) {
+        OPENSSL_free(ctx->ext.alpn);
+        ctx->ext.alpn = NULL;
         ctx->ext.alpn_len = 0;
+        return 0;
+    }
+    /* Not valid per RFC */
+    if (!alpn_value_ok(protos, protos_len))
+        return 1;
+
+    alpn = OPENSSL_memdup(protos, protos_len);
+    if (alpn == NULL) {
         SSLerr(SSL_F_SSL_CTX_SET_ALPN_PROTOS, ERR_R_MALLOC_FAILURE);
         return 1;
     }
+    OPENSSL_free(ctx->ext.alpn);
+    ctx->ext.alpn = alpn;
     ctx->ext.alpn_len = protos_len;
 
     return 0;
@@ -2857,13 +2882,25 @@ int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const unsigned char *protos,
 int SSL_set_alpn_protos(SSL *ssl, const unsigned char *protos,
                         unsigned int protos_len)
 {
-    OPENSSL_free(ssl->ext.alpn);
-    ssl->ext.alpn = OPENSSL_memdup(protos, protos_len);
-    if (ssl->ext.alpn == NULL) {
+    unsigned char *alpn;
+
+    if (protos_len == 0 || protos == NULL) {
+        OPENSSL_free(ssl->ext.alpn);
+        ssl->ext.alpn = NULL;
         ssl->ext.alpn_len = 0;
+        return 0;
+    }
+    /* Not valid per RFC */
+    if (!alpn_value_ok(protos, protos_len))
+        return 1;
+
+    alpn = OPENSSL_memdup(protos, protos_len);
+    if (alpn == NULL) {
         SSLerr(SSL_F_SSL_SET_ALPN_PROTOS, ERR_R_MALLOC_FAILURE);
         return 1;
     }
+    OPENSSL_free(ssl->ext.alpn);
+    ssl->ext.alpn = alpn;
     ssl->ext.alpn_len = protos_len;
 
     return 0;