[PATCH AUTOSEL 5.2 31/85] cifs: Fix a race condition with cifs_echo_request

[PATCH AUTOSEL 5.2 31/85] cifs: Fix a race condition with cifs_echo_request

[Sasha Levin]

From: Ronnie Sahlberg <lsahlber@redhat.com>

[ Upstream commit f2caf901c1b7ce65f9e6aef4217e3241039db768 ]

There is a race condition with how we send (or supress and don't send)
smb echos that will cause the client to incorrectly think the
server is unresponsive and thus needs to be reconnected.

Summary of the race condition:
 1) Daisy chaining scheduling creates a gap.
 2) If traffic comes unfortunate shortly after
    the last echo, the planned echo is suppressed.
 3) Due to the gap, the next echo transmission is delayed
    until after the timeout, which is set hard to twice
    the echo interval.

This is fixed by changing the timeouts from 2 to three times the echo interval.

Detailed description of the bug: https://lutz.donnerhacke.de/eng/Blog/Groundhog-Day-with-SMB-remount

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/connect.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 8dd6637a3cbb..0872188ce3c6 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -706,10 +706,10 @@ static bool
 server_unresponsive(struct TCP_Server_Info *server)
 {
 	/*
-	 * We need to wait 2 echo intervals to make sure we handle such
+	 * We need to wait 3 echo intervals to make sure we handle such
 	 * situations right:
 	 * 1s  client sends a normal SMB request
-	 * 2s  client gets a response
+	 * 3s  client gets a response
 	 * 30s echo workqueue job pops, and decides we got a response recently
 	 *     and don't need to send another
 	 * ...
@@ -718,9 +718,9 @@ server_unresponsive(struct TCP_Server_Info *server)
 	 */
 	if ((server->tcpStatus == CifsGood ||
 	    server->tcpStatus == CifsNeedNegotiate) &&
-	    time_after(jiffies, server->lstrp + 2 * server->echo_interval)) {
+	    time_after(jiffies, server->lstrp + 3 * server->echo_interval)) {
 		cifs_dbg(VFS, "Server %s has not responded in %lu seconds. Reconnecting...\n",
-			 server->hostname, (2 * server->echo_interval) / HZ);
+			 server->hostname, (3 * server->echo_interval) / HZ);
 		cifs_reconnect(server);
 		wake_up(&server->response_q);
 		return true;
-- 
2.20.1

[PATCH AUTOSEL 5.2 41/85] cifs: fix crash in cifs_dfs_do_automount

[Sasha Levin]

From: Ronnie Sahlberg <lsahlber@redhat.com>

[ Upstream commit ce465bf94b70f03136171a62b607864f00093b19 ]

RHBZ: 1649907

Fix a crash that happens while attempting to mount a DFS referral from the same server on the root of a filesystem.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/connect.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 0872188ce3c6..e508613f09ff 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -4459,11 +4459,13 @@ cifs_are_all_path_components_accessible(struct TCP_Server_Info *server,
 					unsigned int xid,
 					struct cifs_tcon *tcon,
 					struct cifs_sb_info *cifs_sb,
-					char *full_path)
+					char *full_path,
+					int added_treename)
 {
 	int rc;
 	char *s;
 	char sep, tmp;
+	int skip = added_treename ? 1 : 0;
 
 	sep = CIFS_DIR_SEP(cifs_sb);
 	s = full_path;
@@ -4478,7 +4480,14 @@ cifs_are_all_path_components_accessible(struct TCP_Server_Info *server,
 		/* next separator */
 		while (*s && *s != sep)
 			s++;
-
+		/*
+		 * if the treename is added, we then have to skip the first
+		 * part within the separators
+		 */
+		if (skip) {
+			skip = 0;
+			continue;
+		}
 		/*
 		 * temporarily null-terminate the path at the end of
 		 * the current component
@@ -4526,8 +4535,7 @@ static int is_path_remote(struct cifs_sb_info *cifs_sb, struct smb_vol *vol,
 
 	if (rc != -EREMOTE) {
 		rc = cifs_are_all_path_components_accessible(server, xid, tcon,
-							     cifs_sb,
-							     full_path);
+			cifs_sb, full_path, tcon->Flags & SMB_SHARE_IS_IN_DFS);
 		if (rc != 0) {
 			cifs_dbg(VFS, "cannot query dirs between root and final path, "
 				 "enabling CIFS_MOUNT_USE_PREFIX_PATH\n");
-- 
2.20.1