smb3: improve SMB3 change notification support

Change notification is a commonly supported feature by most servers,
but the current ioctl to request notification when a directory is
changed does not return the information about what changed
(even though it is returned by the server in the SMB3 change
notify response), it simply returns when there is a change.

This ioctl improves upon CIFS_IOC_NOTIFY by returning the notify
information structure which includes the name of the file(s) that
changed and why. See MS-SMB2 2.2.35 for details on the individual
filter flags and the file_notify_information structure returned.

To use this simply pass in the following (with enough space
to fit at least one file_notify_information structure)

struct __attribute__((__packed__)) smb3_notify {
       uint32_t completion_filter;
       bool     watch_tree;
       uint32_t data_len;
       uint8_t  data[];
} __packed;

using CIFS_IOC_NOTIFY_INFO 0xc009cf0b
 or equivalently _IOWR(CIFS_IOCTL_MAGIC, 11, struct smb3_notify_info)

The ioctl will block until the server detects a change to that
directory or its subdirectories (if watch_tree is set).

Acked-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 27 insertions, 3 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index f8f89ff96c5d..a2384509ea84 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -3710,11 +3710,13 @@ SMB2_notify_init(const unsigned int xid, struct smb_rqst *rqst,
 int
 SMB2_change_notify(const unsigned int xid, struct cifs_tcon *tcon,
 		u64 persistent_fid, u64 volatile_fid, bool watch_tree,
-		u32 completion_filter)
+		u32 completion_filter, u32 max_out_data_len, char **out_data,
+		u32 *plen /* returned data len */)
 {
 	struct cifs_ses *ses = tcon->ses;
 	struct TCP_Server_Info *server = cifs_pick_channel(ses);
 	struct smb_rqst rqst;
+	struct smb2_change_notify_rsp *smb_rsp;
 	struct kvec iov[1];
 	struct kvec rsp_iov = {NULL, 0};
 	int resp_buftype = CIFS_NO_BUFFER;
@@ -3730,6 +3732,9 @@ SMB2_change_notify(const unsigned int xid, struct cifs_tcon *tcon,
 
 	memset(&rqst, 0, sizeof(struct smb_rqst));
 	memset(&iov, 0, sizeof(iov));
+	if (plen)
+		*plen = 0;
+
 	rqst.rq_iov = iov;
 	rqst.rq_nvec = 1;
 
@@ -3748,9 +3753,28 @@ SMB2_change_notify(const unsigned int xid, struct cifs_tcon *tcon,
 		cifs_stats_fail_inc(tcon, SMB2_CHANGE_NOTIFY_HE);
 		trace_smb3_notify_err(xid, persistent_fid, tcon->tid, ses->Suid,
 				(u8)watch_tree, completion_filter, rc);
-	} else
+	} else {
 		trace_smb3_notify_done(xid, persistent_fid, tcon->tid,
-				ses->Suid, (u8)watch_tree, completion_filter);
+			ses->Suid, (u8)watch_tree, completion_filter);
+		/* validate that notify information is plausible */
+		if ((rsp_iov.iov_base == NULL) ||
+		    (rsp_iov.iov_len < sizeof(struct smb2_change_notify_rsp)))
+			goto cnotify_exit;
+
+		smb_rsp = (struct smb2_change_notify_rsp *)rsp_iov.iov_base;
+
+		smb2_validate_iov(le16_to_cpu(smb_rsp->OutputBufferOffset),
+				le32_to_cpu(smb_rsp->OutputBufferLength), &rsp_iov,
+				sizeof(struct file_notify_information));
+
+		*out_data = kmemdup((char *)smb_rsp + le16_to_cpu(smb_rsp->OutputBufferOffset),
+				le32_to_cpu(smb_rsp->OutputBufferLength), GFP_KERNEL);
+		if (*out_data == NULL) {
+			rc = -ENOMEM;
+			goto cnotify_exit;
+		} else
+			*plen = le32_to_cpu(smb_rsp->OutputBufferLength);
+	}
 
  cnotify_exit:
 	if (rqst.rq_iov)