cifs: avoid race conditions with parallel reconnects

When multiple processes/channels do reconnects in parallel
we used to return success immediately
negotiate/session-setup/tree-connect, causing race conditions
between processes that enter the function in parallel.
This caused several errors related to session not found to
show up during parallel reconnects.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 26 insertions, 18 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index caeb92a69b5f..a9fb95b7ef82 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -203,6 +203,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	}
 	spin_unlock(&server->srv_lock);
 
+again:
 	rc = cifs_wait_for_server_reconnect(server, tcon->retry);
 	if (rc)
 		return rc;
@@ -221,6 +222,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 
 	nls_codepage = load_nls_default();
 
+	mutex_lock(&ses->session_mutex);
 	/*
 	 * Recheck after acquire mutex. If another thread is negotiating
 	 * and the server never sends an answer the socket will be closed
@@ -229,6 +231,11 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	spin_lock(&server->srv_lock);
 	if (server->tcpStatus == CifsNeedReconnect) {
 		spin_unlock(&server->srv_lock);
+		mutex_unlock(&ses->session_mutex);
+
+		if (tcon->retry)
+			goto again;
+
 		rc = -EHOSTDOWN;
 		goto out;
 	}
@@ -238,19 +245,22 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	 * need to prevent multiple threads trying to simultaneously
 	 * reconnect the same SMB session
 	 */
+	spin_lock(&ses->ses_lock);
 	spin_lock(&ses->chan_lock);
-	if (!cifs_chan_needs_reconnect(ses, server)) {
+	if (!cifs_chan_needs_reconnect(ses, server) &&
+	    ses->ses_status == SES_GOOD) {
 		spin_unlock(&ses->chan_lock);
-
+		spin_unlock(&ses->ses_lock);
 		/* this means that we only need to tree connect */
 		if (tcon->need_reconnect)
 			goto skip_sess_setup;
 
+		mutex_unlock(&ses->session_mutex);
 		goto out;
 	}
 	spin_unlock(&ses->chan_lock);
+	spin_unlock(&ses->ses_lock);
 
-	mutex_lock(&ses->session_mutex);
 	rc = cifs_negotiate_protocol(0, ses, server);
 	if (!rc) {
 		rc = cifs_setup_session(0, ses, server, nls_codepage);
@@ -266,10 +276,8 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 		mutex_unlock(&ses->session_mutex);
 		goto out;
 	}
-	mutex_unlock(&ses->session_mutex);
 
 skip_sess_setup:
-	mutex_lock(&ses->session_mutex);
 	if (!tcon->need_reconnect) {
 		mutex_unlock(&ses->session_mutex);
 		goto out;
@@ -284,7 +292,7 @@ skip_sess_setup:
 	cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);
 	if (rc) {
 		/* If sess reconnected but tcon didn't, something strange ... */
-		pr_warn_once("reconnect tcon failed rc = %d\n", rc);
+		cifs_dbg(VFS, "reconnect tcon failed rc = %d\n", rc);
 		goto out;
 	}
 
@@ -1256,9 +1264,9 @@ SMB2_sess_alloc_buffer(struct SMB2_sess_data *sess_data)
 	if (rc)
 		return rc;
 
-	spin_lock(&ses->chan_lock);
-	is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
-	spin_unlock(&ses->chan_lock);
+	spin_lock(&ses->ses_lock);
+	is_binding = (ses->ses_status == SES_GOOD);
+	spin_unlock(&ses->ses_lock);
 
 	if (is_binding) {
 		req->hdr.SessionId = cpu_to_le64(ses->Suid);
@@ -1416,9 +1424,9 @@ SMB2_auth_kerberos(struct SMB2_sess_data *sess_data)
 		goto out_put_spnego_key;
 	}
 
-	spin_lock(&ses->chan_lock);
-	is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
-	spin_unlock(&ses->chan_lock);
+	spin_lock(&ses->ses_lock);
+	is_binding = (ses->ses_status == SES_GOOD);
+	spin_unlock(&ses->ses_lock);
 
 	/* keep session key if binding */
 	if (!is_binding) {
@@ -1542,9 +1550,9 @@ SMB2_sess_auth_rawntlmssp_negotiate(struct SMB2_sess_data *sess_data)
 
 	cifs_dbg(FYI, "rawntlmssp session setup challenge phase\n");
 
-	spin_lock(&ses->chan_lock);
-	is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
-	spin_unlock(&ses->chan_lock);
+	spin_lock(&ses->ses_lock);
+	is_binding = (ses->ses_status == SES_GOOD);
+	spin_unlock(&ses->ses_lock);
 
 	/* keep existing ses id and flags if binding */
 	if (!is_binding) {
@@ -1610,9 +1618,9 @@ SMB2_sess_auth_rawntlmssp_authenticate(struct SMB2_sess_data *sess_data)
 
 	rsp = (struct smb2_sess_setup_rsp *)sess_data->iov[0].iov_base;
 
-	spin_lock(&ses->chan_lock);
-	is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
-	spin_unlock(&ses->chan_lock);
+	spin_lock(&ses->ses_lock);
+	is_binding = (ses->ses_status == SES_GOOD);
+	spin_unlock(&ses->ses_lock);
 
 	/* keep existing ses id and flags if binding */
 	if (!is_binding) {