[PATCH 3.16 232/366] cifs: Fix infinite loop when using hard mount option

Ben Hutchings
2018-11-12T06:06:31Z

From: Paulo Alcantara <paulo@paulo.ac>

commit 7ffbe65578b44fafdef577a360eb0583929f7c6e upstream.

For every request we send, whether it is SMB1 or SMB2+, we attempt to
reconnect tcon (cifs_reconnect_tcon or smb2_reconnect) before carrying
out the request.

So, while server->tcpStatus != CifsNeedReconnect, we wait for the
reconnection to succeed on wait_event_interruptible_timeout(). If it
returns, that means that either the condition was evaluated to true, or
timeout elapsed, or it was interrupted by a signal.

Since we're not handling the case where the process woke up due to a
received signal (-ERESTARTSYS), the next call to
wait_event_interruptible_timeout() will _always_ fail and we end up
looping forever inside either cifs_reconnect_tcon() or smb2_reconnect().

Here's an example of how to trigger that:

$ mount.cifs //foo/share /mnt/test -o
username=foo,password=foo,vers=1.0,hard

(break connection to server before executing bellow cmd)
$ stat -f /mnt/test & sleep 140
[1] 2511

$ ps -aux -q 2511
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 2511 0.0 0.0 12892 1008 pts/0 S 12:24 0:00 stat -f
/mnt/test

$ kill -9 2511

(wait for a while; process is stuck in the kernel)
$ ps -aux -q 2511
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 2511 83.2 0.0 12892 1008 pts/0 R 12:24 30:01 stat -f
/mnt/test

By using 'hard' mount point means that cifs.ko will keep retrying
indefinitely, however we must allow the process to be killed otherwise
it would hang the system.

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/cifs/cifssmb.c | 10 ++++++++--
fs/cifs/smb2pdu.c | 18 ++++++++++++------
2 files changed, 20 insertions(+), 8 deletions(-)

--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -150,8 +150,14 @@ cifs_reconnect_tcon(struct cifs_tcon *tc
* greater than cifs socket timeout which is 7 seconds
*/
while (server->tcpStatus == CifsNeedReconnect) {
- wait_event_interruptible_timeout(server->response_q,
- (server->tcpStatus != CifsNeedReconnect), 10 * HZ);
+ rc = wait_event_interruptible_timeout(server->response_q,
+ (server->tcpStatus != CifsNeedReconnect),
+ 10 * HZ);
+ if (rc < 0) {
+ cifs_dbg(FYI, "%s: aborting reconnect due to a received"
+ " signal by the process\n", __func__);
+ return -ERESTARTSYS;
+ }

/* are we still trying to reconnect? */
if (server->tcpStatus != CifsNeedReconnect)
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -158,7 +158,7 @@ out:
static int
smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
{
- int rc = 0;
+ int rc;
struct nls_table *nls_codepage;
struct cifs_ses *ses;
struct TCP_Server_Info *server;
@@ -169,10 +169,10 @@ smb2_reconnect(__le16 smb2_command, stru
* for those three - in the calling routine.
*/
if (tcon == NULL)
- return rc;
+ return 0;

if (smb2_command == SMB2_TREE_CONNECT)
- return rc;
+ return 0;

if (tcon->tidStatus == CifsExiting) {
/*
@@ -215,8 +215,14 @@ smb2_reconnect(__le16 smb2_command, stru
return -EAGAIN;
}

- wait_event_interruptible_timeout(server->response_q,
- (server->tcpStatus != CifsNeedReconnect), 10 * HZ);
+ rc = wait_event_interruptible_timeout(server->response_q,
+ (server->tcpStatus != CifsNeedReconnect),
+ 10 * HZ);
+ if (rc < 0) {
+ cifs_dbg(FYI, "%s: aborting reconnect due to a received"
+ " signal by the process\n", __func__);
+ return -ERESTARTSYS;
+ }

/* are we still trying to reconnect? */
if (server->tcpStatus != CifsNeedReconnect)
@@ -234,7 +240,7 @@ smb2_reconnect(__le16 smb2_command, stru
}

if (!tcon->ses->need_reconnect && !tcon->need_reconnect)
- return rc;
+ return 0;

nls_codepage = load_nls_default();