ring: purge timer before we unmap tx ring buffers

If we unmap TX ring buffers and still have timer shots that trigger
the kernel to traverse the TX_RING, it can send out random crap in
some situations. Prevent this by destroying the timer and flush the
TX_RING first in wait mode.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

5 files changed, 44 insertions, 4 deletions

diff --git a/netsniff-ng.c b/netsniff-ng.c
index 0f97acd..ecb9e9a 100644
--- a/netsniff-ng.c
+++ b/netsniff-ng.c
@@ -131,6 +131,21 @@ static void timer_elapsed(int unused)
 	setitimer(ITIMER_REAL, &itimer, NULL);
 }
 
+static void timer_purge(void)
+{
+	int ret;
+
+	ret = pull_and_flush_tx_ring_wait(tx_sock);
+	if (unlikely(ret < 0)) {
+		if (errno != EBADF && errno != ENOBUFS)
+			panic("Flushing TX_RING failed: %s!\n", strerror(errno));
+	}
+
+	set_itimer_interval_value(&itimer, 0, 0);
+	setitimer(ITIMER_REAL, &itimer, NULL);
+}
+
+
 static void timer_next_dump(int unused)
 {
 	set_itimer_interval_value(&itimer, interval, 0);
@@ -289,6 +304,8 @@ static void pcap_to_xmit(struct ctx *ctx)
 	bug_on(gettimeofday(&end, NULL));
 	timersub(&end, &start, &diff);
 
+	timer_purge();
+
 	bpf_release(&bpf_ops);
 
 	dissector_cleanup_all();
@@ -455,6 +472,8 @@ static void receive_to_xmit(struct ctx *ctx)
 
 	out:
 
+	timer_purge();
+
 	sock_print_net_stats(rx_sock, 0);
 
 	bpf_release(&bpf_ops);
diff --git a/ring_rx.c b/ring_rx.c
index 5675a81..d89d762 100644
--- a/ring_rx.c
+++ b/ring_rx.c
@@ -30,7 +30,7 @@ void destroy_rx_ring(int sock, struct ring *ring)
 	ret = setsockopt(sock, SOL_PACKET, PACKET_RX_RING, &ring->layout,
 			 sizeof(ring->layout));
 	if (unlikely(ret))
-		panic("Cannot destroy the RX_RING!\n");
+		panic("Cannot destroy the RX_RING: %s!\n", strerror(errno));
 
 	xfree(ring->frames);
 }
diff --git a/ring_tx.c b/ring_tx.c
index 6804c43..2ad1de9 100644
--- a/ring_tx.c
+++ b/ring_tx.c
@@ -40,7 +40,7 @@ void destroy_tx_ring(int sock, struct ring *ring)
 	ret = setsockopt(sock, SOL_PACKET, PACKET_TX_RING, &ring->layout,
 			 sizeof(ring->layout));
 	if (unlikely(ret))
-		panic("Cannot destroy the TX_RING!\n");
+		panic("Cannot destroy the TX_RING: %s!\n", strerror(errno));
 
 	xfree(ring->frames);
 }
diff --git a/ring_tx.h b/ring_tx.h
index 7970045..769f27e 100644
--- a/ring_tx.h
+++ b/ring_tx.h
@@ -37,4 +37,9 @@ static inline int pull_and_flush_tx_ring(int sock)
 	return sendto(sock, NULL, 0, MSG_DONTWAIT, NULL, 0);
 }
 
+static inline int pull_and_flush_tx_ring_wait(int sock)
+{
+	return sendto(sock, NULL, 0, 0, NULL, 0);
+}
+
 #endif /* TX_RING_H */
diff --git a/trafgen.c b/trafgen.c
index dc0c54b..fb41f45 100644
--- a/trafgen.c
+++ b/trafgen.c
@@ -127,11 +127,24 @@ static void signal_handler(int number)
 
 static void timer_elapsed(int number)
 {
-	int ret;
+	int ret = pull_and_flush_tx_ring(sock);
+	if (unlikely(ret < 0)) {
+		/* We could hit EBADF if the socket has been closed before
+		 * the timer was triggered.
+		 */
+		if (errno != EBADF && errno != ENOBUFS)
+			panic("Flushing TX_RING failed: %s!\n", strerror(errno));
+	}
 
 	set_itimer_interval_value(&itimer, 0, interval);
+	setitimer(ITIMER_REAL, &itimer, NULL); 
+}
 
-	ret = pull_and_flush_tx_ring(sock);
+static void timer_purge(void)
+{
+	int ret;
+
+	ret = pull_and_flush_tx_ring_wait(sock);
 	if (unlikely(ret < 0)) {
 		/* We could hit EBADF if the socket has been closed before
 		 * the timer was triggered.
@@ -140,6 +153,7 @@ static void timer_elapsed(int number)
 			panic("Flushing TX_RING failed: %s!\n", strerror(errno));
 	}
 
+	set_itimer_interval_value(&itimer, 0, 0);
 	setitimer(ITIMER_REAL, &itimer, NULL); 
 }
 
@@ -669,6 +683,8 @@ static void xmit_fastpath_or_die(struct ctx *ctx, int cpu, unsigned long orig_nu
 	bug_on(gettimeofday(&end, NULL));
 	timersub(&end, &start, &diff);
 
+	timer_purge();
+
 	destroy_tx_ring(sock, &tx_ring);
 
 	stats[cpu].tx_packets = tx_packets;