CIFS: Fix a possible memory corruption during reconnect

We can not unlock/lock cifs_tcp_ses_lock while walking through ses
and tcon lists because it can corrupt list iterator pointers and
a tcon structure can be released if we don't hold an extra reference.
Fix it by moving a reconnect process to a separate delayed work
and acquiring a reference to every tcon that needs to be reconnected.
Also do not send an echo request on newly established connections.

CC: Stable <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 5563de3c64fd..5aaf7b1359a5 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -52,6 +52,9 @@
 #include "nterr.h"
 #include "rfc1002pdu.h"
 #include "fscache.h"
+#ifdef CONFIG_CIFS_SMB2
+#include "smb2proto.h"
+#endif
 
 #define CIFS_PORT 445
 #define RFC1001_PORT 139
@@ -2110,8 +2113,8 @@ cifs_find_tcp_session(struct smb_vol *vol)
 	return NULL;
 }
 
-static void
-cifs_put_tcp_session(struct TCP_Server_Info *server)
+void
+cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
 {
 	struct task_struct *task;
 
@@ -2128,6 +2131,19 @@ cifs_put_tcp_session(struct TCP_Server_Info *server)
 
 	cancel_delayed_work_sync(&server->echo);
 
+#ifdef CONFIG_CIFS_SMB2
+	if (from_reconnect)
+		/*
+		 * Avoid deadlock here: reconnect work calls
+		 * cifs_put_tcp_session() at its end. Need to be sure
+		 * that reconnect work does nothing with server pointer after
+		 * that step.
+		 */
+		cancel_delayed_work(&server->reconnect);
+	else
+		cancel_delayed_work_sync(&server->reconnect);
+#endif
+
 	spin_lock(&GlobalMid_Lock);
 	server->tcpStatus = CifsExiting;
 	spin_unlock(&GlobalMid_Lock);
@@ -2192,6 +2208,10 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
 	INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
 	INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
 	INIT_DELAYED_WORK(&tcp_ses->echo, cifs_echo_request);
+#ifdef CONFIG_CIFS_SMB2
+	INIT_DELAYED_WORK(&tcp_ses->reconnect, smb2_reconnect_server);
+	mutex_init(&tcp_ses->reconnect_mutex);
+#endif
 	memcpy(&tcp_ses->srcaddr, &volume_info->srcaddr,
 	       sizeof(tcp_ses->srcaddr));
 	memcpy(&tcp_ses->dstaddr, &volume_info->dstaddr,
@@ -2350,7 +2370,7 @@ cifs_put_smb_ses(struct cifs_ses *ses)
 	spin_unlock(&cifs_tcp_ses_lock);
 
 	sesInfoFree(ses);
-	cifs_put_tcp_session(server);
+	cifs_put_tcp_session(server, 0);
 }
 
 #ifdef CONFIG_KEYS
@@ -2524,7 +2544,7 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb_vol *volume_info)
 		mutex_unlock(&ses->session_mutex);
 
 		/* existing SMB ses has a server reference already */
-		cifs_put_tcp_session(server);
+		cifs_put_tcp_session(server, 0);
 		free_xid(xid);
 		return ses;
 	}
@@ -2620,7 +2640,7 @@ cifs_find_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 	return NULL;
 }
 
-static void
+void
 cifs_put_tcon(struct cifs_tcon *tcon)
 {
 	unsigned int xid;
@@ -3824,7 +3844,7 @@ mount_fail_check:
 		else if (ses)
 			cifs_put_smb_ses(ses);
 		else
-			cifs_put_tcp_session(server);
+			cifs_put_tcp_session(server, 0);
 		bdi_destroy(&cifs_sb->bdi);
 	}
 
@@ -4135,7 +4155,7 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, kuid_t fsuid)
 	ses = cifs_get_smb_ses(master_tcon->ses->server, vol_info);
 	if (IS_ERR(ses)) {
 		tcon = (struct cifs_tcon *)ses;
-		cifs_put_tcp_session(master_tcon->ses->server);
+		cifs_put_tcp_session(master_tcon->ses->server, 0);
 		goto out;
 	}