crypto: always reload tls-auth/crypt key contexts

In preparation to having tls-auth/crypt keys per connection block, it is important to ensure that such material is always reloaded upon SIGUSR1, no matter if persist-key was specified or not.

This is required because when moving from one remote to the other the key may change and thus the key context needs to be refreshed.

To ensure that the persist-key logic will still work as expected, the tls-auth/crypt key is pre-loaded so that the keyfile is not required at runtime.

Trac: #720

Cc Steffan Karger <[email protected]...>

Signed-off-by Antonio Quartulli <[email protected]...>

---

v2:
- introduce this patch
v3:
- add key per-loading logic to this patch to avoid temporary features

breakages

In preparation to having tls-auth/crypt keys per connection block, it is important to ensure that such material is always reloaded upon SIGUSR1, no matter if persist-key was specified or not.

Quoted 4 lines · Antonio Quartulli

In preparation to having tls-auth/crypt keys per connection block, it is important to ensure that such material is always reloaded upon SIGUSR1, no matter if persist-key was specified or not.

Has this been tested with --chroot and --user/--group?

Hi,

Quoted 1 line · David Sommerseth

On 05/06/18 10:14, Antonio Quartulli wrote:

Quoted 6 lines

Quoted 4 lines

In preparation to having tls-auth/crypt keys per connection block, it is important to ensure that such material is always reloaded upon SIGUSR1, no matter if persist-key was specified or not.

Has this been tested with --chroot and --user/--group?

No, these tests are missing.

In preparation to having tls-auth/crypt keys per connection block, it is important to ensure that such material is always reloaded upon SIGUSR1, no matter if persist-key was specified or not.

This is required because when moving from one remote to the other the key may change and thus the key context needs to be refreshed.

To ensure that the persist-key logic will still work as expected, the tls-auth/crypt key is pre-loaded so that the keyfile is not required at runtime.

Trac: #720

Cc Steffan Karger <[email protected]...>

Signed-off-by Antonio Quartulli <[email protected]...>

---

v2:
- introduce this patch
v3:
- add key per-loading logic to this patch to avoid temporary features breakages

 src/openvpn/buffer.c  | 29 +++++++++++++++
 src/openvpn/buffer.h  | 13 +++++++
 src/openvpn/crypto.c  | 20 ++--------
 src/openvpn/init.c    | 87 ++++++++++++++++++++++++++++---------------
 src/openvpn/options.c | 20 ++++++++++
 5 files changed, 122 insertions(+), 47 deletions(-)

src/openvpn/buffer.c +19 -0

index becfeb93..cbf969a8 100644
@@ -1332,3 +1332,32 @@ buffer_list_file(const char *fn, int max_line_len)
     }
     return bl;
 }
+
+struct buffer
+keyfile_to_buffer(const char *file, int max_size, struct gc_arena *gc)
+{
+    size_t size;
+    struct buffer in = alloc_buf_gc(max_size, gc);
+    int fd = platform_open(file, O_RDONLY, 0);
+    if (fd == -1)
+    {
+        msg(M_ERR, "Cannot open key file '%s'", file);
+    }
+
+    size = read(fd, in.data, in.capacity);
+    if (size < 0)
+    {
+        msg(M_FATAL, "Read error on key file ('%s')", file);
+    }
+
+    if (size == in.capacity)

src/openvpn/buffer.h +13 -0

index d848490a..ba9857eb 100644
@@ -1112,4 +1112,17 @@ void buffer_list_aggregate_separator(struct buffer_list *bl,
 
 struct buffer_list *buffer_list_file(const char *fn, int max_line_len);
 
+/**
+ * keyfile_to_buffer - copy the content of a file into a buffer
+ *
+ * @param file      path to the file to read
+ * @param max_size  maximum size of the buffer to allocate
+ * @param gc        the garbage collector to use when allocating the buffer. It
+ *                  passed to alloc_buf_gc() and therefore can be NULL.
+ *
+ * @return the buffer storing the file content
+ */
+struct buffer keyfile_to_buffer(const char *file, int max_size,
+                                struct gc_arena *gc);
+
 #endif /* BUFFER_H */

src/openvpn/crypto.c +3 -17

index b59c1f73..f201b533 100644
@@ -1224,7 +1224,7 @@ read_key_file(struct key2 *key2, const char *file, const unsigned int flags)
 {
     struct gc_arena gc = gc_new();
     struct buffer in;
-    int fd, size;
+    int size;
     uint8_t hex_byte[3] = {0, 0, 0};
     const char *error_filename = file;
 

@@ -1268,22 +1268,8 @@ read_key_file(struct key2 *key2, const char *file, const unsigned int flags)
     }
     else /* 'file' is a filename which refers to a file containing the ascii key */
     {
-        in = alloc_buf_gc(2048, &gc);
-        fd = platform_open(file, O_RDONLY, 0);
-        if (fd == -1)
-        {
-            msg(M_ERR, "Cannot open key file '%s'", file);
-        }
-        size = read(fd, in.data, in.capacity);
-        if (size < 0)
-        {
-            msg(M_FATAL, "Read error on key file ('%s')", file);
-        }
-        if (size == in.capacity)
-        {
-            msg(M_FATAL, "Key file ('%s') can be a maximum of %d bytes", file, (int)in.capacity);
-        }
-        close(fd);
+        in = keyfile_to_buffer(file, 2048, &gc);
+        size = in.len;
     }
 
     cp = (unsigned char *)in.data;

src/openvpn/init.c +57 -30

index 36c1a4c4..15fef08d 100644
@@ -2406,7 +2406,6 @@ key_schedule_free(struct key_schedule *ks, bool free_ssl_ctx)
     if (tls_ctx_initialised(&ks->ssl_ctx) && free_ssl_ctx)
     {
         tls_ctx_free(&ks->ssl_ctx);
-        free_key_ctx_bi(&ks->tls_wrap_key);
     }
     CLEAR(*ks);
 }

@@ -2496,6 +2495,48 @@ do_init_crypto_static(struct context *c, const unsigned int flags)
     check_replay_consistency(&c->c1.ks.key_type, options->replay);
 }
 
+/*
+ * Initialize the tls-auth/crypt key context
+ */
+static void
+do_init_tls_wrap_key(struct context *c)
+{
+    const struct options *options = &c->options;
+
+    /* TLS handshake authentication (--tls-auth) */
+    if (options->tls_auth_file)
+    {
+        /* Initialize key_type for tls-auth with auth only */
+        CLEAR(c->c1.ks.tls_auth_key_type);
+        if (!streq(options->authname, "none"))
+        {
+            c->c1.ks.tls_auth_key_type.digest = md_kt_get(options->authname);
+                c->c1.ks.tls_auth_key_type.hmac_length =
+                    md_kt_size(c->c1.ks.tls_auth_key_type.digest);
+        }
+        else
+        {
+            msg(M_FATAL, "ERROR: tls-auth enabled, but no valid --auth "
+                "algorithm specified ('%s')", options->authname);
+        }
+
+        crypto_read_openvpn_key(&c->c1.ks.tls_auth_key_type,
+                                &c->c1.ks.tls_wrap_key,
+                                options->tls_auth_file,
+                                options->tls_auth_file_inline,
+                                options->key_direction,
+                                "Control Channel Authentication", "tls-auth");
+    }
+
+    /* TLS handshake encryption+authentication (--tls-crypt) */
+    if (options->tls_crypt_file)
+    {
+        tls_crypt_init_key(&c->c1.ks.tls_wrap_key,
+                           options->tls_crypt_file,
+                           options->tls_crypt_inline, options->tls_server);
+    }
+}
+
 /*
  * Initialize the persistent component of OpenVPN's TLS mode,
  * which is preserved across SIGUSR1 resets.

@@ -2545,35 +2586,8 @@ do_init_crypto_tls_c1(struct context *c)
         /* Initialize PRNG with config-specified digest */
         prng_init(options->prng_hash, options->prng_nonce_secret_len);
 
-        /* TLS handshake authentication (--tls-auth) */
-        if (options->tls_auth_file)
-        {
-            /* Initialize key_type for tls-auth with auth only */
-            CLEAR(c->c1.ks.tls_auth_key_type);
-            if (!streq(options->authname, "none"))
-            {
-                c->c1.ks.tls_auth_key_type.digest = md_kt_get(options->authname);
-                c->c1.ks.tls_auth_key_type.hmac_length =
-                    md_kt_size(c->c1.ks.tls_auth_key_type.digest);
-            }
-            else
-            {
-                msg(M_FATAL, "ERROR: tls-auth enabled, but no valid --auth "
-                    "algorithm specified ('%s')", options->authname);
-            }
-
-            crypto_read_openvpn_key(&c->c1.ks.tls_auth_key_type,
-                                    &c->c1.ks.tls_wrap_key, options->tls_auth_file,
-                                    options->tls_auth_file_inline, options->key_direction,
-                                    "Control Channel Authentication", "tls-auth");
-        }
-
-        /* TLS handshake encryption+authentication (--tls-crypt) */
-        if (options->tls_crypt_file)
-        {
-            tls_crypt_init_key(&c->c1.ks.tls_wrap_key, options->tls_crypt_file,
-                               options->tls_crypt_inline, options->tls_server);
-        }
+        /* initialize tls-auth/crypt key */
+        do_init_tls_wrap_key(c);
 
         c->c1.ciphername = options->ciphername;
         c->c1.authname = options->authname;

@@ -2595,6 +2609,12 @@ do_init_crypto_tls_c1(struct context *c)
         c->options.ciphername = c->c1.ciphername;
         c->options.authname = c->c1.authname;
         c->options.keysize = c->c1.keysize;
+
+        /*
+         * tls-auth/crypt key can be configured per connection block, therefore
+         * we must reload it as it may have changed
+         */
+        do_init_tls_wrap_key(c);
     }
 }
 

@@ -3398,6 +3418,13 @@ do_close_tls(struct context *c)
 static void
 do_close_free_key_schedule(struct context *c, bool free_ssl_ctx)
 {
+    /*
+     * always free the tls_auth/crypt key. If persist_key is true, the key will
+     * be reloaded from memory (pre-cached)
+     */
+    free_key_ctx_bi(&c->c1.ks.tls_wrap_key);
+    CLEAR(c->c1.ks.tls_wrap_key);
+
     if (!(c->sig->signal_received == SIGUSR1 && c->options.persist_key))
     {
         key_schedule_free(&c->c1.ks, free_ssl_ctx);

src/openvpn/options.c +13 -0

index 426057ab..730ca6f1 100644
@@ -3019,6 +3019,26 @@ options_postprocess_mutate(struct options *o)
         options_postprocess_mutate_ce(o, o->connection_list->array[i]);
     }
 
+    /* pre-cache tls-auth/crypt key file if persist-key was specified */
+    if (o->persist_key)
+    {
+        if (o->tls_auth_file && !o->tls_auth_file_inline)
+        {
+            struct buffer in = keyfile_to_buffer(o->tls_auth_file, 2048,
+                                                 &o->gc);
+            o->tls_auth_file = INLINE_FILE_TAG;
+            o->tls_auth_file_inline = (char *)in.data;
+        }
+
+        if (o->tls_crypt_file && !o->tls_crypt_inline)
+        {

Quoted 27 lines

src/openvpn/buffer.c +27 -0

+struct buffer
+keyfile_to_buffer(const char *file, int max_size, struct gc_arena *gc)
+{
+    size_t size;
+    struct buffer in = alloc_buf_gc(max_size, gc);
+    int fd = platform_open(file, O_RDONLY, 0);
+    if (fd == -1)
+    {
+        msg(M_ERR, "Cannot open key file '%s'", file);
+    }
+
+    size = read(fd, in.data, in.capacity);
+    if (size < 0)
+    {
+        msg(M_FATAL, "Read error on key file ('%s')", file);
+    }
+
+    if (size == in.capacity)
+    {
+        msg(M_FATAL, "Key file ('%s') can be a maximum of %d bytes", file,
+            (int)in.capacity);
+    }
+    close(fd);
+
+    in.len = size;
+
+    return in;

Quoted 1 line

+}

Hm, I don't really like the FATAL errors in a function that looks generic enough for someone to use in non-startup situations. In that case the FATALs might create a DoS vector. Or, think ahead to the connection blocks, a connection starting, then timeing out, then exiting because the tls-auth/crypt key of the next connection block doesn't exist (instead of just trying the next block).

While reading this, I realize I wrote a very similar function in the "tls-crypt-v2: generate client keys" patch. That one uses platform_stat() to figure out the size and get rid of the maxlen argument, and doesn't throw fatal errors. Feel free to use that implementation if you like it, or not if you don't (and I'll use yours in the latter case).