From 820962dc700598ffe8cd21b967e30e7520c34748 Mon Sep 17 00:00:00 2001 From: Rabin Vincent Date: Wed, 23 Dec 2015 07:32:41 +0100 Subject: cifs: fix race between call_async() and reconnect() 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 Acked-by: Shirish Pargaonkar CC: Stable Signed-off-by: Steve French --- fs/cifs/transport.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'fs/cifs/transport.c') diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index 2a24c524fb9a..87abe8ed074c 100644 --- 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; } -- cgit v1.2.3