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Subject[PATCH 4.9 23/44] CIFS: Do not reconnect TCP session in add_credits()
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pavel Shilovsky <pshilov@microsoft.com>

commit ef68e831840c40c7d01b328b3c0f5d8c4796c232 upstream.

When executing add_credits() we currently call cifs_reconnect()
if the number of credits is zero and there are no requests in
flight. In this case we may call cifs_reconnect() recursively
twice and cause memory corruption given the following sequence
of functions:

mid1.callback() -> add_credits() -> cifs_reconnect() ->
-> mid2.callback() -> add_credits() -> cifs_reconnect().

Fix this by avoiding to call cifs_reconnect() in add_credits()
and checking for zero credits in the demultiplex thread.

Cc: <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/cifs/connect.c | 21 +++++++++++++++++++++
fs/cifs/smb2ops.c | 32 +++++++++++++++++++++++++-------
2 files changed, 46 insertions(+), 7 deletions(-)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -518,6 +518,21 @@ server_unresponsive(struct TCP_Server_In
return false;
}

+static inline bool
+zero_credits(struct TCP_Server_Info *server)
+{
+ int val;
+
+ spin_lock(&server->req_lock);
+ val = server->credits + server->echo_credits + server->oplock_credits;
+ if (server->in_flight == 0 && val == 0) {
+ spin_unlock(&server->req_lock);
+ return true;
+ }
+ spin_unlock(&server->req_lock);
+ return false;
+}
+
static int
cifs_readv_from_socket(struct TCP_Server_Info *server, struct msghdr *smb_msg)
{
@@ -530,6 +545,12 @@ cifs_readv_from_socket(struct TCP_Server
for (total_read = 0; msg_data_left(smb_msg); total_read += length) {
try_to_freeze();

+ /* reconnect if no credits and no requests in flight */
+ if (zero_credits(server)) {
+ cifs_reconnect(server);
+ return -ECONNABORTED;
+ }
+
if (server_unresponsive(server))
return -ECONNABORTED;

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -30,6 +30,7 @@
#include "smb2glob.h"
#include "cifs_ioctl.h"

+/* Change credits for different ops and return the total number of credits */
static int
change_conf(struct TCP_Server_Info *server)
{
@@ -37,17 +38,15 @@ change_conf(struct TCP_Server_Info *serv
server->oplock_credits = server->echo_credits = 0;
switch (server->credits) {
case 0:
- return -1;
+ return 0;
case 1:
server->echoes = false;
server->oplocks = false;
- cifs_dbg(VFS, "disabling echoes and oplocks\n");
break;
case 2:
server->echoes = true;
server->oplocks = false;
server->echo_credits = 1;
- cifs_dbg(FYI, "disabling oplocks\n");
break;
default:
server->echoes = true;
@@ -60,14 +59,15 @@ change_conf(struct TCP_Server_Info *serv
server->echo_credits = 1;
}
server->credits -= server->echo_credits + server->oplock_credits;
- return 0;
+ return server->credits + server->echo_credits + server->oplock_credits;
}

static void
smb2_add_credits(struct TCP_Server_Info *server, const unsigned int add,
const int optype)
{
- int *val, rc = 0;
+ int *val, rc = -1;
+
spin_lock(&server->req_lock);
val = server->ops->get_credits_field(server, optype);
*val += add;
@@ -91,8 +91,26 @@ smb2_add_credits(struct TCP_Server_Info
}
spin_unlock(&server->req_lock);
wake_up(&server->request_q);
- if (rc)
- cifs_reconnect(server);
+
+ if (server->tcpStatus == CifsNeedReconnect)
+ return;
+
+ switch (rc) {
+ case -1:
+ /* change_conf hasn't been executed */
+ break;
+ case 0:
+ cifs_dbg(VFS, "Possible client or server bug - zero credits\n");
+ break;
+ case 1:
+ cifs_dbg(VFS, "disabling echoes and oplocks\n");
+ break;
+ case 2:
+ cifs_dbg(FYI, "disabling oplocks\n");
+ break;
+ default:
+ cifs_dbg(FYI, "add %u credits total=%d\n", add, rc);
+ }
}

static void

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