CIFS: Fix too big maxBuf size for SMB3 mounts

commit 2365c4ea upstream.

SMB3 servers can respond with MaxTransactSize of more than 4M
that can cause a memory allocation error returned from kmalloc
in a lock codepath. Also the client doesn't support multicredit
requests now and allows buffer sizes of 65536 bytes only. Set
MaxTransactSize to this maximum supported value.
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/cifs/smb2glob.h

@@ -55,4 +55,7 @@
 #define SMB2_NTLMV2_SESSKEY_SIZE (16)
 #define SMB2_HMACSHA256_SIZE (32)
 
+/* Maximum buffer size value we can send with 1 credit */
+#define SMB2_MAX_BUFFER_SIZE 65536
+
 #endif	/* _SMB2_GLOB_H */

fs/cifs/smb2ops.c

@@ -181,11 +181,8 @@ smb2_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
 	/* start with specified wsize, or default */
 	wsize = volume_info->wsize ? volume_info->wsize : CIFS_DEFAULT_IOSIZE;
 	wsize = min_t(unsigned int, wsize, server->max_write);
-	/*
-	 * limit write size to 2 ** 16, because we don't support multicredit
-	 * requests now.
-	 */
-	wsize = min_t(unsigned int, wsize, 2 << 15);
+	/* set it to the maximum buffer size value we can send with 1 credit */
+	wsize = min_t(unsigned int, wsize, SMB2_MAX_BUFFER_SIZE);
 
 	return wsize;
 }
@@ -199,11 +196,8 @@ smb2_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
 	/* start with specified rsize, or default */
 	rsize = volume_info->rsize ? volume_info->rsize : CIFS_DEFAULT_IOSIZE;
 	rsize = min_t(unsigned int, rsize, server->max_read);
-	/*
-	 * limit write size to 2 ** 16, because we don't support multicredit
-	 * requests now.
-	 */
-	rsize = min_t(unsigned int, rsize, 2 << 15);
+	/* set it to the maximum buffer size value we can send with 1 credit */
+	rsize = min_t(unsigned int, rsize, SMB2_MAX_BUFFER_SIZE);
 
 	return rsize;
 }

fs/cifs/smb2pdu.c

@@ -408,6 +408,9 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 	server->dialect = le16_to_cpu(rsp->DialectRevision);
 
 	server->maxBuf = le32_to_cpu(rsp->MaxTransactSize);
+	/* set it to the maximum buffer size value we can send with 1 credit */
+	server->maxBuf = min_t(unsigned int, le32_to_cpu(rsp->MaxTransactSize),
+			       SMB2_MAX_BUFFER_SIZE);
 	server->max_read = le32_to_cpu(rsp->MaxReadSize);
 	server->max_write = le32_to_cpu(rsp->MaxWriteSize);
 	/* BB Do we need to validate the SecurityMode? */