smb: client: validate change notify buffer before copy

SMB2_change_notify called smb2_validate_iov() but ignored the return
code, then kmemdup()ed using server provided OutputBufferOffset/Length.

Check the return of smb2_validate_iov() and bail out on error.

Discovered with help from the ZeroPath security tooling.

Signed-off-by: Joshua Rogers <linux@joshua.hu>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: stable@vger.kernel.org
Fixes: e3e9463 ("smb3: improve SMB3 change notification support")
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Joshua Rogers

fs/smb/client/smb2pdu.c

@@ -4054,9 +4054,12 @@ SMB2_change_notify(const unsigned int xid, struct cifs_tcon *tcon,
 
 		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,
+		rc = smb2_validate_iov(le16_to_cpu(smb_rsp->OutputBufferOffset),
+				le32_to_cpu(smb_rsp->OutputBufferLength),
+				&rsp_iov,
 				sizeof(struct file_notify_information));
+		if (rc)
+			goto cnotify_exit;
 
 		*out_data = kmemdup((char *)smb_rsp + le16_to_cpu(smb_rsp->OutputBufferOffset),
 				le32_to_cpu(smb_rsp->OutputBufferLength), GFP_KERNEL);