This is a note to let you know that I've just added the patch titled cifs: fix race between call_async() and reconnect() to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: cifs-fix-race-between-call_async-and-reconnect.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 820962dc700598ffe8cd21b967e30e7520c34748 Mon Sep 17 00:00:00 2001 From: Rabin Vincent <rabin.vincent@xxxxxxxx> Date: Wed, 23 Dec 2015 07:32:41 +0100 Subject: cifs: fix race between call_async() and reconnect() From: Rabin Vincent <rabin.vincent@xxxxxxxx> 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@xxxxxxxx> Acked-by: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx> Signed-off-by: Steve French <sfrench@localhost.localdomain> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/cifs/connect.c | 2 +- fs/cifs/transport.c | 6 ++++-- 2 files changed, 5 insertions(+), 3 deletions(-) --- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -368,7 +368,6 @@ cifs_reconnect(struct TCP_Server_Info *s 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 *s 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) { --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -576,14 +576,16 @@ cifs_call_async(struct TCP_Server_Info * 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; } Patches currently in stable-queue which might be from rabin.vincent@xxxxxxxx are queue-4.4/cifs-fix-race-between-call_async-and-reconnect.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html