CIFS: Enable signing in SMB2

Use hmac-sha256 and rather than hmac-md5 that is used for CIFS/SMB.

Signature field in SMB2 header is 16 bytes instead of 8 bytes.

Automatically enable signing by client when requested by the server
when signing ability is available to the client.

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 156 insertions, 9 deletions

diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
index 31f5d420b3ea..66479f252ae5 100644
--- a/fs/cifs/smb2transport.c
+++ b/fs/cifs/smb2transport.c
@@ -36,6 +36,149 @@
 #include "smb2proto.h"
 #include "cifs_debug.h"
 #include "smb2status.h"
+#include "smb2glob.h"
+
+static int
+smb2_calc_signature2(const struct kvec *iov, int n_vec,
+                     struct TCP_Server_Info *server)
+{
+        int i, rc;
+        unsigned char smb2_signature[SMB2_HMACSHA256_SIZE];
+        unsigned char *sigptr = smb2_signature;
+        struct smb2_hdr *smb2_pdu = (struct smb2_hdr *)iov[0].iov_base;
+
+        memset(smb2_signature, 0x0, SMB2_HMACSHA256_SIZE);
+        memset(smb2_pdu->Signature, 0x0, SMB2_SIGNATURE_SIZE);
+
+        rc = crypto_shash_setkey(server->secmech.hmacsha256,
+                server->session_key.response, SMB2_NTLMV2_SESSKEY_SIZE);
+        if (rc) {
+                cERROR(1, "%s: Could not update with response\n", __func__);
+                return rc;
+        }
+
+        rc = crypto_shash_init(&server->secmech.sdeschmacsha256->shash);
+        if (rc) {
+                cERROR(1, "%s: Could not init md5\n", __func__);
+                return rc;
+        }
+
+        for (i = 0; i < n_vec; i++) {
+                if (iov[i].iov_len == 0)
+                        continue;
+                if (iov[i].iov_base == NULL) {
+                        cERROR(1, "null iovec entry");
+                        return -EIO;
+                }
+                /*
+                 * The first entry includes a length field (which does not get
+                 * signed that occupies the first 4 bytes before the header).
+                 */
+                if (i == 0) {
+                        if (iov[0].iov_len <= 8) /* cmd field at offset 9 */
+                                break; /* nothing to sign or corrupt header */
+                        rc =
+                        crypto_shash_update(
+                                &server->secmech.sdeschmacsha256->shash,
+                                iov[i].iov_base + 4, iov[i].iov_len - 4);
+                } else {
+                        rc =
+                        crypto_shash_update(
+                                &server->secmech.sdeschmacsha256->shash,
+                                iov[i].iov_base, iov[i].iov_len);
+                }
+                if (rc) {
+                        cERROR(1, "%s: Could not update with payload\n",
+                                                        __func__);
+                        return rc;
+                }
+        }
+
+        rc = crypto_shash_final(&server->secmech.sdeschmacsha256->shash,
+                                sigptr);
+        if (rc)
+                cERROR(1, "%s: Could not generate sha256 hash\n", __func__);
+
+        memcpy(smb2_pdu->Signature, sigptr, SMB2_SIGNATURE_SIZE);
+
+        return rc;
+}
+
+/* must be called with server->srv_mutex held */
+static int
+smb2_sign_smb2(struct kvec *iov, int n_vec, struct TCP_Server_Info *server)
+{
+        int rc = 0;
+        struct smb2_hdr *smb2_pdu = iov[0].iov_base;
+
+        if (!(smb2_pdu->Flags & SMB2_FLAGS_SIGNED) ||
+            server->tcpStatus == CifsNeedNegotiate)
+                return rc;
+
+        if (!server->session_estab) {
+                strncpy(smb2_pdu->Signature, "BSRSPYL", 8);
+                return rc;
+        }
+
+        rc = smb2_calc_signature2(iov, n_vec, server);
+
+        return rc;
+}
+
+int
+smb2_verify_signature2(struct kvec *iov, unsigned int n_vec,
+                       struct TCP_Server_Info *server)
+{
+        unsigned int rc;
+        char server_response_sig[16];
+        struct smb2_hdr *smb2_pdu = (struct smb2_hdr *)iov[0].iov_base;
+
+        if ((smb2_pdu->Command == SMB2_NEGOTIATE) ||
+            (smb2_pdu->Command == SMB2_OPLOCK_BREAK) ||
+            (!server->session_estab))
+                return 0;
+
+        /*
+         * BB what if signatures are supposed to be on for session but
+         * server does not send one? BB
+         */
+
+        /* Do not need to verify session setups with signature "BSRSPYL " */
+        if (memcmp(smb2_pdu->Signature, "BSRSPYL ", 8) == 0)
+                cFYI(1, "dummy signature received for smb command 0x%x",
+                        smb2_pdu->Command);
+
+        /*
+         * Save off the origiginal signature so we can modify the smb and check
+         * our calculated signature against what the server sent.
+         */
+        memcpy(server_response_sig, smb2_pdu->Signature, SMB2_SIGNATURE_SIZE);
+
+        memset(smb2_pdu->Signature, 0, SMB2_SIGNATURE_SIZE);
+
+        mutex_lock(&server->srv_mutex);
+        rc = smb2_calc_signature2(iov, n_vec, server);
+        mutex_unlock(&server->srv_mutex);
+
+        if (rc)
+                return rc;
+
+        if (memcmp(server_response_sig, smb2_pdu->Signature,
+                   SMB2_SIGNATURE_SIZE))
+                return -EACCES;
+        else
+                return 0;
+}
+
+static int
+smb2_verify_signature(struct smb2_hdr *smb2_pdu, struct TCP_Server_Info *server)
+{
+        struct kvec iov;
+
+        iov.iov_base = (char *)smb2_pdu;
+        iov.iov_len = get_rfc1002_length(smb2_pdu) + 4;
+        return smb2_verify_signature2(&iov, 1, server);
+}
 
 /*
  * Set message id for the request. Should be called after wait_for_free_request
@@ -118,12 +261,15 @@ smb2_check_receive(struct mid_q_entry *mid, struct TCP_Server_Info *server,
 
         dump_smb(mid->resp_buf, min_t(u32, 80, len));
         /* convert the length into a more usable form */
-        /* BB - uncomment with SMB2 signing implementation */
-        /* if ((len > 24) &&
+        if ((len > 24) &&
             (server->sec_mode & (SECMODE_SIGN_REQUIRED|SECMODE_SIGN_ENABLED))) {
-                if (smb2_verify_signature(mid->resp_buf, server))
-                        cERROR(1, "Unexpected SMB signature");
-        } */
+                int rc;
+
+                rc = smb2_verify_signature(mid->resp_buf, server);
+                if (rc)
+                        cERROR(1, "SMB signature verification returned error = "
+                               "%d", rc);
+        }
 
         return map_smb2_to_linux_error(mid->resp_buf, log_error);
 }
@@ -141,9 +287,9 @@ smb2_setup_request(struct cifs_ses *ses, struct kvec *iov,
         rc = smb2_get_mid_entry(ses, hdr, &mid);
         if (rc)
                 return rc;
-        /* rc = smb2_sign_smb2(iov, nvec, ses->server);
+        rc = smb2_sign_smb2(iov, nvec, ses->server);
         if (rc)
-                delete_mid(mid); */
+                cifs_delete_mid(mid);
         *ret_mid = mid;
         return rc;
 }
@@ -162,11 +308,12 @@ smb2_setup_async_request(struct TCP_Server_Info *server, struct kvec *iov,
         if (mid == NULL)
                 return -ENOMEM;
 
-        /* rc = smb2_sign_smb2(iov, nvec, server);
+        rc = smb2_sign_smb2(iov, nvec, server);
         if (rc) {
                 DeleteMidQEntry(mid);
                 return rc;
-        }*/
+        }
+
         *ret_mid = mid;
         return rc;
 }