[1/3] cifs: Fix validation of signed data in smb3+

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 lenght is passed so we
make sure there's one (iov_len == 4).

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
---
 fs/cifs/smb2transport.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

Nice. Thanks.

Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

----- Original Message -----
From: "Paulo Alcantara" <paulo@paulo.ac>
To: linux-cifs@vger.kernel.org
Cc: smfrench@gmail.com, "Paulo Alcantara" <paulo@paulo.ac>, "Paulo Alcantara" <palcantara@suse.de>
Sent: Sunday, 24 June, 2018 3:52:23 AM
Subject: [PATCH 1/3] cifs: Fix validation of signed data in smb3+

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 lenght is passed so we
make sure there's one (iov_len == 4).

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
---
 fs/cifs/smb2transport.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
index 50592976dcb4..1af46ca5a951 100644
--- a/fs/cifs/smb2transport.c
+++ b/fs/cifs/smb2transport.c
@@ -408,12 +408,14 @@ generate_smb311signingkey(struct cifs_ses *ses)
 int
 smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 {
-	int rc = 0;
+	int rc;
 	unsigned char smb3_signature[SMB2_CMACAES_SIZE];
 	unsigned char *sigptr = smb3_signature;
 	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.sdesccmacaes->shash;
+	struct smb_rqst drqst;
 
 	ses = smb2_find_smb_ses(server, shdr->SessionId);
 	if (!ses) {
@@ -425,8 +427,7 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	memset(shdr->Signature, 0x0, SMB2_SIGNATURE_SIZE);
 
 	rc = crypto_shash_setkey(server->secmech.cmacaes,
-		ses->smb3signingkey, SMB2_CMACAES_SIZE);
-
+				 ses->smb3signingkey, SMB2_CMACAES_SIZE);
 	if (rc) {
 		cifs_dbg(VFS, "%s: Could not set key for cmac aes\n", __func__);
 		return rc;
@@ -437,15 +438,33 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	 * so unlike smb2 case we do not have to check here if secmech are
 	 * initialized
 	 */
-	rc = crypto_shash_init(&server->secmech.sdesccmacaes->shash);
+	rc = crypto_shash_init(shash);
 	if (rc) {
 		cifs_dbg(VFS, "%s: Could not init cmac aes\n", __func__);
 		return rc;
 	}
 
-	rc = __cifs_calc_signature(rqst, server, sigptr,
-				   &server->secmech.sdesccmacaes->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);