cifs: fix potential use-after-free bugs in TCP_Server_Info::hostname

TCP_Server_Info::hostname may be updated once or many times during
reconnect, so protect its access outside reconnect path as well and
then prevent any potential use-after-free bugs.

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

fs/cifs/cifs_debug.c

@@ -280,8 +280,10 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 		seq_printf(m, "\n%d) ConnectionId: 0x%llx ",
 			c, server->conn_id);
 
+		spin_lock(&server->srv_lock);
 		if (server->hostname)
 			seq_printf(m, "Hostname: %s ", server->hostname);
+		spin_unlock(&server->srv_lock);
 #ifdef CONFIG_CIFS_SMB_DIRECT
 		if (!server->rdma)
 			goto skip_rdma;
@@ -623,10 +625,13 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 				server->fastest_cmd[j],
 				server->slowest_cmd[j]);
 		for (j = 0; j < NUMBER_OF_SMB2_COMMANDS; j++)
-			if (atomic_read(&server->smb2slowcmd[j]))
+			if (atomic_read(&server->smb2slowcmd[j])) {
+				spin_lock(&server->srv_lock);
 				seq_printf(m, "  %d slow responses from %s for command %d\n",
 					atomic_read(&server->smb2slowcmd[j]),
 					server->hostname, j);
+				spin_unlock(&server->srv_lock);
+			}
 #endif /* STATS2 */
 		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
 			list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {

fs/cifs/cifs_debug.h

@@ -81,19 +81,19 @@ do {									\
 
 #define cifs_server_dbg_func(ratefunc, type, fmt, ...)			\
 do {									\
-	const char *sn = "";						\
-	if (server && server->hostname)					\
-		sn = server->hostname;					\
+	spin_lock(&server->srv_lock);					\
 	if ((type) & FYI && cifsFYI & CIFS_INFO) {			\
 		pr_debug_ ## ratefunc("%s: \\\\%s " fmt,		\
-				      __FILE__, sn, ##__VA_ARGS__);	\
+				      __FILE__, server->hostname,	\
+				      ##__VA_ARGS__);			\
 	} else if ((type) & VFS) {					\
 		pr_err_ ## ratefunc("VFS: \\\\%s " fmt,			\
-				    sn, ##__VA_ARGS__);			\
+				    server->hostname, ##__VA_ARGS__);	\
 	} else if ((type) & NOISY && (NOISY != 0)) {			\
 		pr_debug_ ## ratefunc("\\\\%s " fmt,			\
-				      sn, ##__VA_ARGS__);		\
+				      server->hostname, ##__VA_ARGS__);	\
 	}								\
+	spin_unlock(&server->srv_lock);					\
 } while (0)
 
 #define cifs_server_dbg(type, fmt, ...)					\

fs/cifs/connect.c

@@ -403,8 +403,10 @@ static int __reconnect_target_unlocked(struct TCP_Server_Info *server, const cha
 		if (server->hostname != target) {
 			hostname = extract_hostname(target);
 			if (!IS_ERR(hostname)) {
+				spin_lock(&server->srv_lock);
 				kfree(server->hostname);
 				server->hostname = hostname;
+				spin_unlock(&server->srv_lock);
 			} else {
 				cifs_dbg(FYI, "%s: couldn't extract hostname or address from dfs target: %ld\n",
 					 __func__, PTR_ERR(hostname));
@@ -561,9 +563,7 @@ cifs_echo_request(struct work_struct *work)
 		goto requeue_echo;
 
 	rc = server->ops->echo ? server->ops->echo(server) : -ENOSYS;
-	if (rc)
-		cifs_dbg(FYI, "Unable to send echo request to server: %s\n",
-			 server->hostname);
+	cifs_server_dbg(FYI, "send echo request: rc = %d\n", rc);
 
 	/* Check witness registrations */
 	cifs_swn_check();
@@ -1404,6 +1404,8 @@ static int match_server(struct TCP_Server_Info *server, struct smb3_fs_context *
 {
 	struct sockaddr *addr = (struct sockaddr *)&ctx->dstaddr;
 
+	lockdep_assert_held(&server->srv_lock);
+
 	if (ctx->nosharesock)
 		return 0;
 
@@ -1810,7 +1812,9 @@ cifs_setup_ipc(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 	if (tcon == NULL)
 		return -ENOMEM;
 
+	spin_lock(&server->srv_lock);
 	scnprintf(unc, sizeof(unc), "\\\\%s\\IPC$", server->hostname);
+	spin_unlock(&server->srv_lock);
 
 	xid = get_xid();
 	tcon->ses = ses;

fs/cifs/sess.c

@@ -159,6 +159,7 @@ cifs_chan_is_iface_active(struct cifs_ses *ses,
 /* returns number of channels added */
 int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
 {
+	struct TCP_Server_Info *server = ses->server;
 	int old_chan_count, new_chan_count;
 	int left;
 	int rc = 0;
@@ -178,16 +179,16 @@ int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
 		return 0;
 	}
 
-	if (ses->server->dialect < SMB30_PROT_ID) {
+	if (server->dialect < SMB30_PROT_ID) {
 		spin_unlock(&ses->chan_lock);
 		cifs_dbg(VFS, "multichannel is not supported on this protocol version, use 3.0 or above\n");
 		return 0;
 	}
 
-	if (!(ses->server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) {
+	if (!(server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) {
 		ses->chan_max = 1;
 		spin_unlock(&ses->chan_lock);
-		cifs_dbg(VFS, "server %s does not support multichannel\n", ses->server->hostname);
+		cifs_server_dbg(VFS, "no multichannel support\n");
 		return 0;
 	}
 	spin_unlock(&ses->chan_lock);