cifs: track the enablement of signing in the TCP_Server_Info

Currently, we determine this according to flags in the sec_mode, flags
in the global_secflags and via other methods. That makes the semantics
very hard to follow and there are corner cases where we don't handle
this correctly.

Add a new bool to the TCP_Server_Info that acts as a simple flag to tell
us whether signing is enabled on this connection or not, and fix up the
places that need to determine this to use that flag.

This is a bit weird for the SMB2 case, where signing is per-session.
SMB2 needs work in this area already though. The existing SMB2 code has
similar logic to what we're using here, so there should be no real
change in behavior. These changes should make it easier to implement
per-session signing in the future though.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 41 insertions, 35 deletions

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 80ca6886a816..dd7e2f61f607 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -418,32 +418,43 @@ decode_ext_sec_blob(struct TCP_Server_Info *server, NEGOTIATE_RSP *pSMBr)
 }
 
 int
-cifs_enable_signing(struct TCP_Server_Info *server, unsigned int secFlags)
+cifs_enable_signing(struct TCP_Server_Info *server, bool mnt_sign_required)
 {
-	if ((secFlags & CIFSSEC_MAY_SIGN) == 0) {
-		/* MUST_SIGN already includes the MAY_SIGN FLAG
-		   so if this is zero it means that signing is disabled */
-		cifs_dbg(FYI, "Signing disabled\n");
-		if (server->sec_mode & SECMODE_SIGN_REQUIRED) {
-			cifs_dbg(VFS, "Server requires packet signing to be enabled in /proc/fs/cifs/SecurityFlags\n");
-			return -EOPNOTSUPP;
+	bool srv_sign_required = server->sec_mode & SECMODE_SIGN_REQUIRED;
+	bool srv_sign_enabled = server->sec_mode & SECMODE_SIGN_ENABLED;
+	bool mnt_sign_enabled = global_secflags & CIFSSEC_MAY_SIGN;
+
+	/*
+	 * Is signing required by mnt options? If not then check
+	 * global_secflags to see if it is there.
+	 */
+	if (!mnt_sign_required)
+		mnt_sign_required = ((global_secflags & CIFSSEC_MUST_SIGN) ==
+						CIFSSEC_MUST_SIGN);
+
+	/*
+	 * If signing is required then it's automatically enabled too,
+	 * otherwise, check to see if the secflags allow it.
+	 */
+	mnt_sign_enabled = mnt_sign_required ? mnt_sign_required :
+				(global_secflags & CIFSSEC_MAY_SIGN);
+
+	/* If server requires signing, does client allow it? */
+	if (srv_sign_required) {
+		if (!mnt_sign_enabled) {
+			cifs_dbg(VFS, "Server requires signing, but it's disabled in SecurityFlags!");
+			return -ENOTSUPP;
 		}
-		server->sec_mode &=
-			~(SECMODE_SIGN_ENABLED | SECMODE_SIGN_REQUIRED);
-	} else if ((secFlags & CIFSSEC_MUST_SIGN) == CIFSSEC_MUST_SIGN) {
-		/* signing required */
-		cifs_dbg(FYI, "Must sign - secFlags 0x%x\n", secFlags);
-		if ((server->sec_mode &
-			(SECMODE_SIGN_ENABLED | SECMODE_SIGN_REQUIRED)) == 0) {
-			cifs_dbg(VFS, "signing required but server lacks support\n");
-			return -EOPNOTSUPP;
-		} else
-			server->sec_mode |= SECMODE_SIGN_REQUIRED;
-	} else {
-		/* signing optional ie CIFSSEC_MAY_SIGN */
-		if ((server->sec_mode & SECMODE_SIGN_REQUIRED) == 0)
-			server->sec_mode &=
-				~(SECMODE_SIGN_ENABLED | SECMODE_SIGN_REQUIRED);
+		server->sign = true;
+	}
+
+	/* If client requires signing, does server allow it? */
+	if (mnt_sign_required) {
+		if (!srv_sign_enabled) {
+			cifs_dbg(VFS, "Server does not support signing!");
+			return -ENOTSUPP;
+		}
+		server->sign = true;
 	}
 
 	return 0;
@@ -685,7 +696,7 @@ CIFSSMBNegotiate(const unsigned int xid, struct cifs_ses *ses)
 
 signing_check:
 	if (!rc)
-		rc = cifs_enable_signing(server, secFlags);
+		rc = cifs_enable_signing(server, ses->sign);
 neg_err_exit:
 	cifs_buf_release(pSMB);
 
@@ -810,9 +821,8 @@ CIFSSMBLogoff(const unsigned int xid, struct cifs_ses *ses)
 
 	pSMB->hdr.Mid = get_next_mid(ses->server);
 
-	if (ses->server->sec_mode &
-		   (SECMODE_SIGN_REQUIRED | SECMODE_SIGN_ENABLED))
-			pSMB->hdr.Flags2 |= SMBFLG2_SECURITY_SIGNATURE;
+	if (ses->server->sign)
+		pSMB->hdr.Flags2 |= SMBFLG2_SECURITY_SIGNATURE;
 
 	pSMB->hdr.Uid = ses->Suid;
 
@@ -1573,8 +1583,7 @@ cifs_readv_callback(struct mid_q_entry *mid)
 	switch (mid->mid_state) {
 	case MID_RESPONSE_RECEIVED:
 		/* result already set, check signature */
-		if (server->sec_mode &
-		    (SECMODE_SIGN_REQUIRED | SECMODE_SIGN_ENABLED)) {
+		if (server->sign) {
 			int rc = 0;
 
 			rc = cifs_verify_signature(&rqst, server,
@@ -4827,11 +4836,8 @@ getDFSRetry:
 		strncpy(pSMB->RequestFileName, search_name, name_len);
 	}
 
-	if (ses->server) {
-		if (ses->server->sec_mode &
-		   (SECMODE_SIGN_REQUIRED | SECMODE_SIGN_ENABLED))
-			pSMB->hdr.Flags2 |= SMBFLG2_SECURITY_SIGNATURE;
-	}
+	if (ses->server && ses->server->sign)
+		pSMB->hdr.Flags2 |= SMBFLG2_SECURITY_SIGNATURE;
 
 	pSMB->hdr.Uid = ses->Suid;