CIFS: Mask off signals when sending SMB packets

We don't want to break SMB sessions if we receive signals when
sending packets through the network. Fix it by masking off signals
inside __smb_send_rqst() to avoid partial packet sends due to
interrupts.

Return -EINTR if a signal is pending and only a part of the packet
was sent. Return a success status code if the whole packet was sent
regardless of signal being pending or not. This keeps a mid entry
for the request in the pending queue and allows the demultiplex
thread to handle a response from the server properly.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/transport.c

@@ -33,6 +33,7 @@
 #include <linux/uaccess.h>
 #include <asm/processor.h>
 #include <linux/mempool.h>
+#include <linux/signal.h>
 #include "cifspdu.h"
 #include "cifsglob.h"
 #include "cifsproto.h"
@@ -291,6 +292,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 	int n_vec;
 	unsigned int send_length = 0;
 	unsigned int i, j;
+	sigset_t mask, oldmask;
 	size_t total_len = 0, sent, size;
 	struct socket *ssocket = server->ssocket;
 	struct msghdr smb_msg;
@@ -305,6 +307,11 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 	if (ssocket == NULL)
 		return -EAGAIN;
 
+	if (signal_pending(current)) {
+		cifs_dbg(FYI, "signal is pending before sending any data\n");
+		return -EINTR;
+	}
+
 	/* cork the socket */
 	kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,
 				(char *)&val, sizeof(val));
@@ -313,6 +320,16 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 		send_length += smb_rqst_len(server, &rqst[j]);
 	rfc1002_marker = cpu_to_be32(send_length);
 
+	/*
+	 * We should not allow signals to interrupt the network send because
+	 * any partial send will cause session reconnects thus increasing
+	 * latency of system calls and overload a server with unnecessary
+	 * requests.
+	 */
+
+	sigfillset(&mask);
+	sigprocmask(SIG_BLOCK, &mask, &oldmask);
+
 	/* Generate a rfc1002 marker for SMB2+ */
 	if (server->vals->header_preamble_size == 0) {
 		struct kvec hiov = {
@@ -322,7 +339,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 		iov_iter_kvec(&smb_msg.msg_iter, WRITE, &hiov, 1, 4);
 		rc = smb_send_kvec(server, &smb_msg, &sent);
 		if (rc < 0)
-			goto uncork;
+			goto unmask;
 
 		total_len += sent;
 		send_length += 4;
@@ -344,7 +361,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 
 		rc = smb_send_kvec(server, &smb_msg, &sent);
 		if (rc < 0)
-			goto uncork;
+			goto unmask;
 
 		total_len += sent;
 
@@ -366,7 +383,25 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 		}
 	}
 
-uncork:
+unmask:
+	sigprocmask(SIG_SETMASK, &oldmask, NULL);
+
+	/*
+	 * If signal is pending but we have already sent the whole packet to
+	 * the server we need to return success status to allow a corresponding
+	 * mid entry to be kept in the pending requests queue thus allowing
+	 * to handle responses from the server by the client.
+	 *
+	 * If only part of the packet has been sent there is no need to hide
+	 * interrupt because the session will be reconnected anyway, so there
+	 * won't be any response from the server to handle.
+	 */
+
+	if (signal_pending(current) && (total_len != send_length)) {
+		cifs_dbg(FYI, "signal is pending after attempt to send\n");
+		rc = -EINTR;
+	}
+
 	/* uncork it */
 	val = 0;
 	kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,