Add mod_session support

By setting GssapiUseSessions we enable the module to store a bearer
token with the user and gss names in the client, this way we can allow
clients to perform authentication once but then remain authenticaed
for the duration of the session or until the original credentials expire.

The Secure cookie used to store the token is encrypted using a randomly
generated AES key at process startup. This means multiple apache servers
will not be able to use the same cookie, however the client will reauth
transparently if the cookie cannot be read.

1 files changed, 210 insertions, 0 deletions

diff --git a/src/crypto.c b/src/crypto.c
new file mode 100644
index 0000000..9be58e5
--- /dev/null
+++ b/src/crypto.c
@@ -0,0 +1,210 @@
+/* Copyright (C) 2014 mod_auth_gssapi authors - See COPYING for (C) terms */
+
+#include <openssl/evp.h>
+#include <openssl/hmac.h>
+#include <openssl/rand.h>
+#include <stdbool.h>
+#include "crypto.h"
+
+struct seal_key {
+    const EVP_CIPHER *cipher;
+    const EVP_MD *md;
+    unsigned char *ekey;
+    unsigned char *hkey;
+};
+
+apr_status_t SEAL_KEY_CREATE(struct seal_key **skey)
+{
+    struct seal_key *n;
+    int ret;
+
+    n = calloc(1, sizeof(*n));
+    if (!n) return ENOMEM;
+
+    n->cipher = EVP_aes_128_cbc();
+    if (!n->cipher) {
+        free(n);
+        return EFAULT;
+    }
+
+    n->md = EVP_sha256();
+    if (!n->md) {
+        free(n);
+        return EFAULT;
+    }
+
+    n->ekey = malloc(n->cipher->key_len);
+    if (!n->ekey) {
+        free(n);
+        return ENOMEM;
+    }
+
+    n->hkey = malloc(n->cipher->key_len);
+    if (!n->hkey) {
+        free(n);
+        return ENOMEM;
+    }
+
+    ret = RAND_bytes(n->ekey, n->cipher->key_len);
+    if (ret == 0) {
+        free(n->ekey);
+        free(n->hkey);
+        free(n);
+        return EFAULT;
+    }
+
+    ret = RAND_bytes(n->hkey, n->cipher->key_len);
+    if (ret == 0) {
+        free(n->ekey);
+        free(n->hkey);
+        free(n);
+        return EFAULT;
+    }
+
+    *skey = n;
+    return 0;
+}
+
+apr_status_t SEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                         struct databuf *plain, struct databuf *cipher)
+{
+    apr_status_t err = EFAULT;
+    EVP_CIPHER_CTX ctx = { 0 };
+    HMAC_CTX hmac_ctx = { 0 };
+    uint8_t rbuf[16];
+    unsigned int len;
+    int outlen, totlen;
+    int ret;
+
+    EVP_CIPHER_CTX_init(&ctx);
+
+    /* confounder to avoid exposing random numbers directly to clients
+     * as IVs */
+    ret = RAND_bytes(rbuf, 16);
+    if (ret == 0) goto done;
+
+    if (cipher->length == 0) {
+        /* add space for confounder and padding and MAC */
+        cipher->length = (plain->length / 16 + 2) * 16;
+        cipher->value = apr_palloc(p, cipher->length + skey->md->md_size);
+        if (!cipher->value) {
+            err = ENOMEM;
+            goto done;
+        }
+    }
+
+    ret = EVP_EncryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
+    if (ret == 0) goto done;
+    totlen = 0;
+
+    outlen = cipher->length;
+    ret = EVP_EncryptUpdate(&ctx, cipher->value, &outlen, rbuf, 16);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    outlen = cipher->length - totlen;
+    ret = EVP_EncryptUpdate(&ctx, &cipher->value[totlen], &outlen,
+                            plain->value, plain->length);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    outlen = cipher->length - totlen;
+    ret = EVP_EncryptFinal_ex(&ctx, &cipher->value[totlen], &outlen);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    /* now MAC the buffer */
+    HMAC_CTX_init(&hmac_ctx);
+
+    ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
+                       skey->cipher->key_len, skey->md, NULL);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Update(&hmac_ctx, cipher->value, totlen);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Final(&hmac_ctx, &cipher->value[totlen], &len);
+    if (ret == 0) goto done;
+
+    cipher->length = totlen + len;
+    err = 0;
+
+done:
+    EVP_CIPHER_CTX_cleanup(&ctx);
+    HMAC_CTX_cleanup(&hmac_ctx);
+    return err;
+}
+
+apr_status_t UNSEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                           struct databuf *cipher, struct databuf *plain)
+{
+    apr_status_t err = EFAULT;
+    EVP_CIPHER_CTX ctx = { 0 };
+    HMAC_CTX hmac_ctx = { 0 };
+    unsigned char mac[skey->md->md_size];
+    unsigned int len;
+    int outlen, totlen;
+    volatile bool equal = true;
+    int ret, i;
+
+    /* check MAC first */
+    HMAC_CTX_init(&hmac_ctx);
+
+    ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
+                       skey->cipher->key_len, skey->md, NULL);
+    if (ret == 0) goto done;
+
+    cipher->length -= skey->md->md_size;
+
+    ret = HMAC_Update(&hmac_ctx, cipher->value, cipher->length);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Final(&hmac_ctx, mac, &len);
+    if (ret == 0) goto done;
+
+    if (len != skey->md->md_size) goto done;
+    for (i = 0; i < skey->md->md_size; i++) {
+        if (cipher->value[cipher->length + i] != mac[i]) equal = false;
+        /* not breaking intentionally,
+         * or we would allow an oracle attack */
+    }
+    if (!equal) goto done;
+
+    EVP_CIPHER_CTX_init(&ctx);
+
+    if (plain->length == 0) {
+        plain->length = cipher->length;
+        plain->value = apr_palloc(p, plain->length);
+        if (!plain->value) {
+            err = ENOMEM;
+            goto done;
+        }
+    }
+
+    ret = EVP_DecryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
+    if (ret == 0) goto done;
+
+    totlen = 0;
+    outlen = plain->length;
+    ret = EVP_DecryptUpdate(&ctx, plain->value, &outlen,
+                            cipher->value, cipher->length);
+    if (ret == 0) goto done;
+
+    totlen += outlen;
+    outlen = plain->length - totlen;
+    ret = EVP_DecryptFinal_ex(&ctx, plain->value, &outlen);
+    if (ret == 0) goto done;
+
+    totlen += outlen;
+    /* now remove the confounder */
+    totlen -= 16;
+    memmove(plain->value, plain->value + 16, totlen);
+
+    plain->length = totlen;
+    err = 0;
+
+done:
+    EVP_CIPHER_CTX_cleanup(&ctx);
+    HMAC_CTX_cleanup(&hmac_ctx);
+    return err;
+}