Commit eb2c033d authored by Rabin Vincent's avatar Rabin Vincent Committed by Luis Henriques

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

commit 820962dc 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: default avatarRabin Vincent <rabin.vincent@axis.com>
Acked-by: default avatarShirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: default avatarSteve French <sfrench@localhost.localdomain>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent b51db3dc
......@@ -354,7 +354,6 @@ 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);
......@@ -367,6 +366,7 @@ 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) {
......
......@@ -564,14 +564,16 @@ 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(server, 1, optype);
wake_up(&server->request_q);
return rc;
......
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