Re: [PATCH v2 4/5] CIFS: Fix a possible memory corruption during reconnect

[Sachin Prabhu <sprabhu-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Mon, 2016-12-05 at 13:11 -0800, Pavel Shilovsky wrote:
> We can not unlock/lock cifs_tcp_ses_lock while walking through ses
> and tcon lists because it can corrupt list iterator pointers and
> a tcon structure can be released if we don't hold an extra reference.
> Fix it by moving a reconnect process to a separate delayed work
> and acquiring a reference to every tcon that needs to be reconnected.
> Also do not send an echo request on newly established connections.
> 
> CC: Stable <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
> Signed-off-by: Pavel Shilovsky <pshilov-0li6OtcxBFHby3iVrkZq2A@public.gmane.org>
> ---
>  fs/cifs/cifsglob.h  |  3 +++
>  fs/cifs/cifsproto.h |  3 +++
>  fs/cifs/connect.c   | 34 +++++++++++++++++++-----
>  fs/cifs/smb2pdu.c   | 75 ++++++++++++++++++++++++++++++++++++-------
> ----------
>  fs/cifs/smb2proto.h |  1 +
>  5 files changed, 85 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index 3e95191..89a0d7f 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -647,6 +647,8 @@ struct TCP_Server_Info {
>  	unsigned int	max_read;
>  	unsigned int	max_write;
>  	__u8		preauth_hash[512];
> +	struct delayed_work reconnect; /* reconnect workqueue job */
> +	struct mutex reconnect_mutex; /* prevent simultaneous
> reconnects */
>  #endif /* CONFIG_CIFS_SMB2 */
>  	unsigned long echo_interval;
>  };
> @@ -850,6 +852,7 @@ cap_unix(struct cifs_ses *ses)
>  struct cifs_tcon {
>  	struct list_head tcon_list;
>  	int tc_count;
> +	struct list_head rlist; /* reconnect list */
>  	struct list_head openFileList;
>  	spinlock_t open_file_lock; /* protects list above */
>  	struct cifs_ses *ses;	/* pointer to session
> associated with */
> diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
> index ced0e42..cd8025a 100644
> --- a/fs/cifs/cifsproto.h
> +++ b/fs/cifs/cifsproto.h
> @@ -206,6 +206,9 @@ extern void cifs_add_pending_open_locked(struct
> cifs_fid *fid,
>  					 struct tcon_link *tlink,
>  					 struct cifs_pending_open
> *open);
>  extern void cifs_del_pending_open(struct cifs_pending_open *open);
> +extern void cifs_put_tcp_session(struct TCP_Server_Info *server,
> +				 int from_reconnect);
> +extern void cifs_put_tcon(struct cifs_tcon *tcon);
>  
>  #if IS_ENABLED(CONFIG_CIFS_DFS_UPCALL)
>  extern void cifs_dfs_release_automount_timer(void);
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index 5563de3..5aaf7b1 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -52,6 +52,9 @@
>  #include "nterr.h"
>  #include "rfc1002pdu.h"
>  #include "fscache.h"
> +#ifdef CONFIG_CIFS_SMB2
> +#include "smb2proto.h"
> +#endif
>  
>  #define CIFS_PORT 445
>  #define RFC1001_PORT 139
> @@ -2110,8 +2113,8 @@ cifs_find_tcp_session(struct smb_vol *vol)
>  	return NULL;
>  }
>  
> -static void
> -cifs_put_tcp_session(struct TCP_Server_Info *server)
> +void
> +cifs_put_tcp_session(struct TCP_Server_Info *server, int
> from_reconnect)

The from_reconnect here becomes an unused variable if the kernel is
built without CONFIG_CIFS_SMB2 support. 

>  {
>  	struct task_struct *task;
>  
> @@ -2128,6 +2131,19 @@ cifs_put_tcp_session(struct TCP_Server_Info
> *server)
>  
>  	cancel_delayed_work_sync(&server->echo);
>  
> +#ifdef CONFIG_CIFS_SMB2
> +	if (from_reconnect)
> +		/*
> +		 * Avoid deadlock here: reconnect work calls
> +		 * cifs_put_tcp_session() at its end. Need to be
> sure
> +		 * that reconnect work does nothing with server
> pointer after
> +		 * that step.
> +		 */
> +		cancel_delayed_work(&server->reconnect);
> +	else
> +		cancel_delayed_work_sync(&server->reconnect);
> +#endif
> +
>  	spin_lock(&GlobalMid_Lock);
>  	server->tcpStatus = CifsExiting;
>  	spin_unlock(&GlobalMid_Lock);
> @@ -2192,6 +2208,10 @@ cifs_get_tcp_session(struct smb_vol
> *volume_info)
>  	INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
>  	INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
>  	INIT_DELAYED_WORK(&tcp_ses->echo, cifs_echo_request);
> +#ifdef CONFIG_CIFS_SMB2
> +	INIT_DELAYED_WORK(&tcp_ses->reconnect,
> smb2_reconnect_server);
> +	mutex_init(&tcp_ses->reconnect_mutex);
> +#endif
>  	memcpy(&tcp_ses->srcaddr, &volume_info->srcaddr,
>  	       sizeof(tcp_ses->srcaddr));
>  	memcpy(&tcp_ses->dstaddr, &volume_info->dstaddr,
> @@ -2350,7 +2370,7 @@ cifs_put_smb_ses(struct cifs_ses *ses)
>  	spin_unlock(&cifs_tcp_ses_lock);
>  
>  	sesInfoFree(ses);
> -	cifs_put_tcp_session(server);
> +	cifs_put_tcp_session(server, 0);
>  }
>  
>  #ifdef CONFIG_KEYS
> @@ -2524,7 +2544,7 @@ cifs_get_smb_ses(struct TCP_Server_Info
> *server, struct smb_vol *volume_info)
>  		mutex_unlock(&ses->session_mutex);
>  
>  		/* existing SMB ses has a server reference already
> */
> -		cifs_put_tcp_session(server);
> +		cifs_put_tcp_session(server, 0);
>  		free_xid(xid);
>  		return ses;
>  	}
> @@ -2620,7 +2640,7 @@ cifs_find_tcon(struct cifs_ses *ses, struct
> smb_vol *volume_info)
>  	return NULL;
>  }
>  
> -static void
> +void
>  cifs_put_tcon(struct cifs_tcon *tcon)
>  {
>  	unsigned int xid;
> @@ -3824,7 +3844,7 @@ cifs_mount(struct cifs_sb_info *cifs_sb, struct
> smb_vol *volume_info)
>  		else if (ses)
>  			cifs_put_smb_ses(ses);
>  		else
> -			cifs_put_tcp_session(server);
> +			cifs_put_tcp_session(server, 0);
>  		bdi_destroy(&cifs_sb->bdi);
>  	}
>  
> @@ -4135,7 +4155,7 @@ cifs_construct_tcon(struct cifs_sb_info
> *cifs_sb, kuid_t fsuid)
>  	ses = cifs_get_smb_ses(master_tcon->ses->server, vol_info);
>  	if (IS_ERR(ses)) {
>  		tcon = (struct cifs_tcon *)ses;
> -		cifs_put_tcp_session(master_tcon->ses->server);
> +		cifs_put_tcp_session(master_tcon->ses->server, 0);
>  		goto out;
>  	}
>  
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index 730d57b..4ba3f68 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -1972,6 +1972,54 @@ smb2_echo_callback(struct mid_q_entry *mid)
>  	add_credits(server, credits_received, CIFS_ECHO_OP);
>  }
>  
> +void smb2_reconnect_server(struct work_struct *work)
> +{
> +	struct TCP_Server_Info *server = container_of(work,
> +					struct TCP_Server_Info,
> reconnect.work);
> +	struct cifs_ses *ses;
> +	struct cifs_tcon *tcon, *tcon2;
> +	struct list_head tmp_list;
> +	int tcon_exist = false;
> +
> +	/* Prevent simultaneous reconnects that can corrupt tcon-
> >rlist list */
> +	mutex_lock(&server->reconnect_mutex);
> +
> +	INIT_LIST_HEAD(&tmp_list);
> +	cifs_dbg(FYI, "Need negotiate, reconnecting tcons\n");
> +
> +	spin_lock(&cifs_tcp_ses_lock);
> +	list_for_each_entry(ses, &server->smb_ses_list,
> smb_ses_list) {
> +		list_for_each_entry(tcon, &ses->tcon_list,
> tcon_list) {
> +			if (tcon->need_reconnect) {
> +				tcon->tc_count++;
> +				list_add_tail(&tcon->rlist,
> &tmp_list);
> +				tcon_exist = true;
> +			}
> +		}
> +	}
> +	/*
> +	 * Get the reference to server struct to be sure that the
> last call of
> +	 * cifs_put_tcon() in the loop below won't release the
> server pointer.
> +	 */
> +	if (tcon_exist)
> +		server->srv_count++;
> +
> +	spin_unlock(&cifs_tcp_ses_lock);
> +
> +	list_for_each_entry_safe(tcon, tcon2, &tmp_list, rlist) {
> +		smb2_reconnect(SMB2_ECHO, tcon);
> +		list_del_init(&tcon->rlist);
> +		cifs_put_tcon(tcon);
> +	}
> +
> +	cifs_dbg(FYI, "Reconnecting tcons finished\n");
> +	mutex_unlock(&server->reconnect_mutex);
> +
> +	/* now we can safely release srv struct */
> +	if (tcon_exist)
> +		cifs_put_tcp_session(server, 1);
> +}
> +
>  int
>  SMB2_echo(struct TCP_Server_Info *server)
>  {
> @@ -1984,32 +2032,11 @@ SMB2_echo(struct TCP_Server_Info *server)
>  	cifs_dbg(FYI, "In echo request\n");
>  
>  	if (server->tcpStatus == CifsNeedNegotiate) {
> -		struct list_head *tmp, *tmp2;
> -		struct cifs_ses *ses;
> -		struct cifs_tcon *tcon;
> -
> -		cifs_dbg(FYI, "Need negotiate, reconnecting
> tcons\n");
> -		spin_lock(&cifs_tcp_ses_lock);
> -		list_for_each(tmp, &server->smb_ses_list) {
> -			ses = list_entry(tmp, struct cifs_ses,
> smb_ses_list);
> -			list_for_each(tmp2, &ses->tcon_list) {
> -				tcon = list_entry(tmp2, struct
> cifs_tcon,
> -						  tcon_list);
> -				/* add check for persistent handle
> reconnect */
> -				if (tcon && tcon->need_reconnect) {
> -					spin_unlock(&cifs_tcp_ses_lo
> ck);
> -					rc =
> smb2_reconnect(SMB2_ECHO, tcon);
> -					spin_lock(&cifs_tcp_ses_lock
> );
> -				}
> -			}
> -		}
> -		spin_unlock(&cifs_tcp_ses_lock);
> +		/* No need to send echo on newly established
> connections */
> +		queue_delayed_work(cifsiod_wq, &server->reconnect,
> 0);
> +		return rc;
>  	}
>  
> -	/* if no session, renegotiate failed above */
> -	if (server->tcpStatus == CifsNeedNegotiate)
> -		return -EIO;
> -
>  	rc = small_smb2_init(SMB2_ECHO, NULL, (void **)&req);
>  	if (rc)
>  		return rc;
> diff --git a/fs/cifs/smb2proto.h b/fs/cifs/smb2proto.h
> index eb2cde2..f2d511a 100644
> --- a/fs/cifs/smb2proto.h
> +++ b/fs/cifs/smb2proto.h
> @@ -96,6 +96,7 @@ extern int smb2_open_file(const unsigned int xid,
>  extern int smb2_unlock_range(struct cifsFileInfo *cfile,
>  			     struct file_lock *flock, const unsigned
> int xid);
>  extern int smb2_push_mandatory_locks(struct cifsFileInfo *cfile);
> +extern void smb2_reconnect_server(struct work_struct *work);
>  
>  /*
>   * SMB2 Worker functions - most of protocol specific implementation
> details

Apart from that small nitpick,

Acked-by: Sachin Prabhu <sprabhu-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>