ksmbd: limit read/write/trans buffer size not to exceed 8MB

ksmbd limit read/write/trans buffer size not to exceed maximum 8MB.
And set the minimum value of max response buffer size to 64KB.
Windows client doesn't send session setup request if ksmbd set max
trans/read/write size lower than 64KB in smb2 negotiate.
It means windows allow at least 64 KB or more about this value.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smb2ops.c

@@ -284,6 +284,7 @@ int init_smb3_11_server(struct ksmbd_conn *conn)
 
 void init_smb2_max_read_size(unsigned int sz)
 {
+	sz = clamp_val(sz, SMB3_MIN_IOSIZE, SMB3_MAX_IOSIZE);
 	smb21_server_values.max_read_size = sz;
 	smb30_server_values.max_read_size = sz;
 	smb302_server_values.max_read_size = sz;
@@ -292,6 +293,7 @@ void init_smb2_max_read_size(unsigned int sz)
 
 void init_smb2_max_write_size(unsigned int sz)
 {
+	sz = clamp_val(sz, SMB3_MIN_IOSIZE, SMB3_MAX_IOSIZE);
 	smb21_server_values.max_write_size = sz;
 	smb30_server_values.max_write_size = sz;
 	smb302_server_values.max_write_size = sz;
@@ -300,6 +302,7 @@ void init_smb2_max_write_size(unsigned int sz)
 
 void init_smb2_max_trans_size(unsigned int sz)
 {
+	sz = clamp_val(sz, SMB3_MIN_IOSIZE, SMB3_MAX_IOSIZE);
 	smb21_server_values.max_trans_size = sz;
 	smb30_server_values.max_trans_size = sz;
 	smb302_server_values.max_trans_size = sz;

fs/ksmbd/smb2pdu.c

@@ -524,7 +524,7 @@ int smb2_allocate_rsp_buf(struct ksmbd_work *work)
 {
 	struct smb2_hdr *hdr = work->request_buf;
 	size_t small_sz = MAX_CIFS_SMALL_BUFFER_SIZE;
-	size_t large_sz = work->conn->vals->max_trans_size + MAX_SMB2_HDR_SIZE;
+	size_t large_sz = small_sz + work->conn->vals->max_trans_size;
 	size_t sz = small_sz;
 	int cmd = le16_to_cpu(hdr->Command);
 

fs/ksmbd/smb2pdu.h

@@ -113,6 +113,8 @@
 #define SMB21_DEFAULT_IOSIZE	(1024 * 1024)
 #define SMB3_DEFAULT_IOSIZE	(4 * 1024 * 1024)
 #define SMB3_DEFAULT_TRANS_SIZE	(1024 * 1024)
+#define SMB3_MIN_IOSIZE	(64 * 1024)
+#define SMB3_MAX_IOSIZE	(8 * 1024 * 1024)
 
 /*
  * SMB2 Header Definition