cifs: support mounting with alternate password to allow password rotation

Fixes the case for example where the password specified on mount is a
recently expired password, but password2 is valid.  Without this patch
this mount scenario would fail.

This patch introduces the following changes to support password rotation on
mount:

1. If an existing session is not found and the new session setup results in
EACCES, EKEYEXPIRED or EKEYREVOKED, swap password and password2 (if
available), and retry the mount.

2. To match the new mount with an existing session, add conditions to check
if a) password and password2 of the new mount and the existing session are
the same, or b) password of the new mount is the same as the password2 of
the existing session, and password2 of the new mount is the same as the
password of the existing session.

3. If an existing session is found, but needs reconnect, retry the session
setup after swapping password and password2 (if available), in case the
previous attempt results in EACCES, EKEYEXPIRED or EKEYREVOKED.

Cc: stable@vger.kernel.org
Signed-off-by: Meetakshi Setiya <msetiya@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: meetakshi253

fs/smb/client/connect.c

@@ -1897,11 +1897,35 @@ static int match_session(struct cifs_ses *ses,
 			    CIFS_MAX_USERNAME_LEN))
 			return 0;
 		if ((ctx->username && strlen(ctx->username) != 0) &&
-		    ses->password != NULL &&
-		    strncmp(ses->password,
-			    ctx->password ? ctx->password : "",
-			    CIFS_MAX_PASSWORD_LEN))
-			return 0;
+		    ses->password != NULL) {
+
+			/* New mount can only share sessions with an existing mount if:
+			 * 1. Both password and password2 match, or
+			 * 2. password2 of the old mount matches password of the new mount
+			 *    and password of the old mount matches password2 of the new
+			 *	  mount
+			 */
+			if (ses->password2 != NULL && ctx->password2 != NULL) {
+				if (!((strncmp(ses->password, ctx->password ?
+					ctx->password : "", CIFS_MAX_PASSWORD_LEN) == 0 &&
+					strncmp(ses->password2, ctx->password2,
+					CIFS_MAX_PASSWORD_LEN) == 0) ||
+					(strncmp(ses->password, ctx->password2,
+					CIFS_MAX_PASSWORD_LEN) == 0 &&
+					strncmp(ses->password2, ctx->password ?
+					ctx->password : "", CIFS_MAX_PASSWORD_LEN) == 0)))
+					return 0;
+
+			} else if ((ses->password2 == NULL && ctx->password2 != NULL) ||
+				(ses->password2 != NULL && ctx->password2 == NULL)) {
+				return 0;
+
+			} else {
+				if (strncmp(ses->password, ctx->password ?
+					ctx->password : "", CIFS_MAX_PASSWORD_LEN))
+					return 0;
+			}
+		}
 	}
 
 	if (strcmp(ctx->local_nls->charset, ses->local_nls->charset))
@@ -2244,6 +2268,7 @@ struct cifs_ses *
 cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 {
 	int rc = 0;
+	int retries = 0;
 	unsigned int xid;
 	struct cifs_ses *ses;
 	struct sockaddr_in *addr = (struct sockaddr_in *)&server->dstaddr;
@@ -2262,6 +2287,8 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 			cifs_dbg(FYI, "Session needs reconnect\n");
 
 			mutex_lock(&ses->session_mutex);
+
+retry_old_session:
 			rc = cifs_negotiate_protocol(xid, ses, server);
 			if (rc) {
 				mutex_unlock(&ses->session_mutex);
@@ -2274,6 +2301,13 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 			rc = cifs_setup_session(xid, ses, server,
 						ctx->local_nls);
 			if (rc) {
+				if (((rc == -EACCES) || (rc == -EKEYEXPIRED) ||
+					(rc == -EKEYREVOKED)) && !retries && ses->password2) {
+					retries++;
+					cifs_dbg(FYI, "Session reconnect failed, retrying with alternate password\n");
+					swap(ses->password, ses->password2);
+					goto retry_old_session;
+				}
 				mutex_unlock(&ses->session_mutex);
 				/* problem -- put our reference */
 				cifs_put_smb_ses(ses);
@@ -2369,6 +2403,7 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 	ses->chans_need_reconnect = 1;
 	spin_unlock(&ses->chan_lock);
 
+retry_new_session:
 	mutex_lock(&ses->session_mutex);
 	rc = cifs_negotiate_protocol(xid, ses, server);
 	if (!rc)
@@ -2381,8 +2416,16 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 	       sizeof(ses->smb3signingkey));
 	spin_unlock(&ses->chan_lock);
 
-	if (rc)
-		goto get_ses_fail;
+	if (rc) {
+		if (((rc == -EACCES) || (rc == -EKEYEXPIRED) ||
+			(rc == -EKEYREVOKED)) && !retries && ses->password2) {
+			retries++;
+			cifs_dbg(FYI, "Session setup failed, retrying with alternate password\n");
+			swap(ses->password, ses->password2);
+			goto retry_new_session;
+		} else
+			goto get_ses_fail;
+	}
 
 	/*
 	 * success, put it on the list and add it as first channel