cifs: fix race between call_async() and reconnect()

commit 820962dc700598ffe8cd21b967e30e7520c34748 upstream.

cifs_call_async() queues the MID to the pending list and calls
smb_send_rqst().  If smb_send_rqst() performs a partial send, it sets
the tcpStatus to CifsNeedReconnect and returns an error code to
cifs_call_async().  In this case, cifs_call_async() removes the MID
from the list and returns to the caller.

However, cifs_call_async() releases the server mutex _before_ removing
the MID.  This means that a cifs_reconnect() can race with this function
and manage to remove the MID from the list and delete the entry before
cifs_call_async() calls cifs_delete_mid().  This leads to various
crashes due to the use after free in cifs_delete_mid().

Task1				Task2

cifs_call_async():
 - rc = -EAGAIN
 - mutex_unlock(srv_mutex)

				cifs_reconnect():
				 - mutex_lock(srv_mutex)
				 - mutex_unlock(srv_mutex)
				 - list_delete(mid)
				 - mid->callback()
				 	cifs_writev_callback():
				 		- mutex_lock(srv_mutex)
						- delete(mid)
				 		- mutex_unlock(srv_mutex)

 - cifs_delete_mid(mid) <---- use after free

Fix this by removing the MID in cifs_call_async() before releasing the
srv_mutex.  Also hold the srv_mutex in cifs_reconnect() until the MIDs
are moved out of the pending list.

Signed-off-by: Rabin Vincent <rabin.vincent@axis.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@localhost.localdomain>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index ecb0803..3c194ff 100644 (file)
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -368,7 +368,6 @@ cifs_reconnect(struct TCP_Server_Info *server)
        server->session_key.response = NULL;
        server->session_key.len = 0;
        server->lstrp = jiffies;
-       mutex_unlock(&server->srv_mutex);
 
        /* mark submitted MIDs for retry and issue callback */
        INIT_LIST_HEAD(&retry_list);
@@ -381,6 +380,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
                list_move(&mid_entry->qhead, &retry_list);
        }
        spin_unlock(&GlobalMid_Lock);
+       mutex_unlock(&server->srv_mutex);
 
        cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
        list_for_each_safe(tmp, tmp2, &retry_list) {

diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 2a24c52..87abe8e 100644 (file)
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -576,14 +576,16 @@ cifs_call_async(struct TCP_Server_Info *server, struct smb_rqst *rqst,
        cifs_in_send_dec(server);
        cifs_save_when_sent(mid);
 
-       if (rc < 0)
+       if (rc < 0) {
                server->sequence_number -= 2;
+               cifs_delete_mid(mid);
+       }
+
        mutex_unlock(&server->srv_mutex);
 
        if (rc == 0)
                return 0;
 
-       cifs_delete_mid(mid);
        add_credits_and_wake_if(server, credits, optype);
        return rc;
 }