cifs: Fix validation of signed data in smb2

Fixes: c713c8770fa5 ("cifs: push rfc1002 generation down the stack")

We failed to validate signed data returned by the server because
__cifs_calc_signature() now expects to sign the actual data in iov but
we were also passing down the rfc1002 length.

Fix smb3_calc_signature() to calculate signature of rfc1002 length prior
to passing only the actual data iov[1-N] to __cifs_calc_signature(). In
addition, there are a few cases where no rfc1002 length is passed so we
make sure there's one (iov_len == 4).

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 24 insertions, 4 deletions

diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
index 1af46ca5a951..719d55e63d88 100644
--- a/fs/cifs/smb2transport.c
+++ b/fs/cifs/smb2transport.c
@@ -173,6 +173,8 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
         struct kvec *iov = rqst->rq_iov;
         struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)iov[0].iov_base;
         struct cifs_ses *ses;
+        struct shash_desc *shash = &server->secmech.sdeschmacsha256->shash;
+        struct smb_rqst drqst;
 
         ses = smb2_find_smb_ses(server, shdr->SessionId);
         if (!ses) {
@@ -190,21 +192,39 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
         }
 
         rc = crypto_shash_setkey(server->secmech.hmacsha256,
-                ses->auth_key.response, SMB2_NTLMV2_SESSKEY_SIZE);
+                                 ses->auth_key.response, SMB2_NTLMV2_SESSKEY_SIZE);
         if (rc) {
                 cifs_dbg(VFS, "%s: Could not update with response\n", __func__);
                 return rc;
         }
 
-        rc = crypto_shash_init(&server->secmech.sdeschmacsha256->shash);
+        rc = crypto_shash_init(shash);
         if (rc) {
                 cifs_dbg(VFS, "%s: Could not init sha256", __func__);
                 return rc;
         }
 
-        rc = __cifs_calc_signature(rqst, server, sigptr,
-                &server->secmech.sdeschmacsha256->shash);
+        /*
+         * For SMB2+, __cifs_calc_signature() expects to sign only the actual
+         * data, that is, iov[0] should not contain a rfc1002 length.
+         *
+         * Sign the rfc1002 length prior to passing the data (iov[1-N]) down to
+         * __cifs_calc_signature().
+         */
+        drqst = *rqst;
+        if (drqst.rq_nvec >= 2 && iov[0].iov_len == 4) {
+                rc = crypto_shash_update(shash, iov[0].iov_base,
+                                         iov[0].iov_len);
+                if (rc) {
+                        cifs_dbg(VFS, "%s: Could not update with payload\n",
+                                 __func__);
+                        return rc;
+                }
+                drqst.rq_iov++;
+                drqst.rq_nvec--;
+        }
 
+        rc = __cifs_calc_signature(&drqst, server, sigptr, shash);
         if (!rc)
                 memcpy(shdr->Signature, sigptr, SMB2_SIGNATURE_SIZE);