[PATCH net-next 1/2] ip: fail fast on IP defrag errors

[PATCH net-next 1/2] ip: fail fast on IP defrag errors

[Peter Oskolkov]

The current behavior of IP defragmentation is inconsistent:
- some overlapping/wrong length fragments are dropped without
  affecting the queue;
- most overlapping fragments cause the whole frag queue to be dropped.

This patch brings consistency: if a bad fragment is detected,
the whole frag queue is dropped. Two major benefits:
- fail fast: corrupted frag queues are cleared immediately, instead of
  by timeout;
- testing of overlapping fragments is now much easier: any kind of
  random fragment length mutation now leads to the frag queue being
  discarded (IP packet dropped); before this patch, some overlaps were
  "corrected", with tests not seeing expected packet drops.

Note that in one case (see "if (end&7)" conditional) the current
behavior is preserved as there are concerns that this could be
legitimate padding.

Signed-off-by: Peter Oskolkov <posk@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
 net/ipv4/ip_fragment.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 88281fbce88c..330f62353b11 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -382,7 +382,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		 */
 		if (end < qp->q.len ||
 		    ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
-			goto err;
+			goto discard_qp;
 		qp->q.flags |= INET_FRAG_LAST_IN;
 		qp->q.len = end;
 	} else {
@@ -394,20 +394,20 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		if (end > qp->q.len) {
 			/* Some bits beyond end -> corruption. */
 			if (qp->q.flags & INET_FRAG_LAST_IN)
-				goto err;
+				goto discard_qp;
 			qp->q.len = end;
 		}
 	}
 	if (end == offset)
-		goto err;
+		goto discard_qp;
 
 	err = -ENOMEM;
 	if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
-		goto err;
+		goto discard_qp;
 
 	err = pskb_trim_rcsum(skb, end - offset);
 	if (err)
-		goto err;
+		goto discard_qp;
 
 	/* Note : skb->rbnode and skb->dev share the same location. */
 	dev = skb->dev;
@@ -423,6 +423,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 	 * We do the same here for IPv4 (and increment an snmp counter).
 	 */
 
+	err = -EINVAL;
 	/* Find out where to put this fragment.  */
 	prev_tail = qp->q.fragments_tail;
 	if (!prev_tail)
@@ -431,7 +432,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		/* This is the common case: skb goes to the end. */
 		/* Detect and discard overlaps. */
 		if (offset < prev_tail->ip_defrag_offset + prev_tail->len)
-			goto discard_qp;
+			goto overlap;
 		if (offset == prev_tail->ip_defrag_offset + prev_tail->len)
 			ip4_frag_append_to_last_run(&qp->q, skb);
 		else
@@ -450,7 +451,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 						FRAG_CB(skb1)->frag_run_len)
 				rbn = &parent->rb_right;
 			else /* Found an overlap with skb1. */
-				goto discard_qp;
+				goto overlap;
 		} while (*rbn);
 		/* Here we have parent properly set, and rbn pointing to
 		 * one of its NULL left/right children. Insert skb.
@@ -487,16 +488,18 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		skb->_skb_refdst = 0UL;
 		err = ip_frag_reasm(qp, skb, prev_tail, dev);
 		skb->_skb_refdst = orefdst;
+		if (err)
+			inet_frag_kill(&qp->q);
 		return err;
 	}
 
 	skb_dst_drop(skb);
 	return -EINPROGRESS;
 
+overlap:
+	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
 discard_qp:
 	inet_frag_kill(&qp->q);
-	err = -EINVAL;
-	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
 err:
 	kfree_skb(skb);
 	return err;
-- 
2.19.0.rc0.228.g281dcd1b4d0-goog

[PATCH net-next 2/2] selftests/net: add ip_defrag selftest

[Peter Oskolkov]

This test creates a raw IPv4 socket, fragments a largish UDP
datagram and sends the fragments out of order.

Then repeats in a loop with different message and fragment lengths.

Then does the same with overlapping fragments (with overlapping
fragments the expectation is that the recv times out).

Tested:

root@<host># time ./ip_defrag.sh
ipv4 defrag
PASS
ipv4 defrag with overlaps
PASS

real    1m7.679s
user    0m0.628s
sys     0m2.242s

A similar test for IPv6 is to follow.

Signed-off-by: Peter Oskolkov <posk@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
 tools/testing/selftests/net/.gitignore   |   2 +
 tools/testing/selftests/net/Makefile     |   4 +-
 tools/testing/selftests/net/ip_defrag.c  | 313 +++++++++++++++++++++++
 tools/testing/selftests/net/ip_defrag.sh |  29 +++
 4 files changed, 346 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/net/ip_defrag.c
 create mode 100755 tools/testing/selftests/net/ip_defrag.sh

diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index 78b24cf76f40..2836e0cf2d81 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -14,3 +14,5 @@ udpgso_bench_rx
 udpgso_bench_tx
 tcp_inq
 tls
+ip_defrag
+
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 9cca68e440a0..cccdb2295567 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -5,13 +5,13 @@ CFLAGS =  -Wall -Wl,--no-as-needed -O2 -g
 CFLAGS += -I../../../../usr/include/
 
 TEST_PROGS := run_netsocktests run_afpackettests test_bpf.sh netdevice.sh rtnetlink.sh
-TEST_PROGS += fib_tests.sh fib-onlink-tests.sh pmtu.sh udpgso.sh
+TEST_PROGS += fib_tests.sh fib-onlink-tests.sh pmtu.sh udpgso.sh ip_defrag.sh
 TEST_PROGS += udpgso_bench.sh fib_rule_tests.sh msg_zerocopy.sh psock_snd.sh
 TEST_PROGS_EXTENDED := in_netns.sh
 TEST_GEN_FILES =  socket
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy
 TEST_GEN_FILES += tcp_mmap tcp_inq psock_snd
-TEST_GEN_FILES += udpgso udpgso_bench_tx udpgso_bench_rx
+TEST_GEN_FILES += udpgso udpgso_bench_tx udpgso_bench_rx ip_defrag
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa
 TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls
 
diff --git a/tools/testing/selftests/net/ip_defrag.c b/tools/testing/selftests/net/ip_defrag.c
new file mode 100644
index 000000000000..55fdcdc78eef
--- /dev/null
+++ b/tools/testing/selftests/net/ip_defrag.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <error.h>
+#include <linux/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
+#include <netinet/udp.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+static bool		cfg_do_ipv4;
+static bool		cfg_do_ipv6;
+static bool		cfg_verbose;
+static bool		cfg_overlap;
+static unsigned short	cfg_port = 9000;
+
+const struct in_addr addr4 = { .s_addr = __constant_htonl(INADDR_LOOPBACK + 2) };
+
+#define IP4_HLEN	(sizeof(struct iphdr))
+#define IP6_HLEN	(sizeof(struct ip6_hdr))
+#define UDP_HLEN	(sizeof(struct udphdr))
+
+static int msg_len;
+static int max_frag_len;
+
+#define MSG_LEN_MAX	60000	/* Max UDP payload length. */
+
+#define IP4_MF		(1u << 13)  /* IPv4 MF flag. */
+
+static uint8_t udp_payload[MSG_LEN_MAX];
+static uint8_t ip_frame[IP_MAXPACKET];
+static uint16_t ip_id = 0xabcd;
+static int msg_counter;
+static int frag_counter;
+static unsigned int seed;
+
+/* Receive a UDP packet. Validate it matches udp_payload. */
+static void recv_validate_udp(int fd_udp)
+{
+	ssize_t ret;
+	static uint8_t recv_buff[MSG_LEN_MAX];
+
+	ret = recv(fd_udp, recv_buff, msg_len, 0);
+	msg_counter++;
+
+	if (cfg_overlap) {
+		if (ret != -1)
+			error(1, 0, "recv: expected timeout; got %d; seed = %u",
+				(int)ret, seed);
+		if (errno != ETIMEDOUT && errno != EAGAIN)
+			error(1, errno, "recv: expected timeout: %d; seed = %u",
+				 errno, seed);
+		return;  /* OK */
+	}
+
+	if (ret == -1)
+		error(1, errno, "recv: msg_len = %d max_frag_len = %d",
+			msg_len, max_frag_len);
+	if (ret != msg_len)
+		error(1, 0, "recv: wrong size: %d vs %d", (int)ret, msg_len);
+	if (memcmp(udp_payload, recv_buff, msg_len))
+		error(1, 0, "recv: wrong data");
+}
+
+static uint32_t raw_checksum(uint8_t *buf, int len, uint32_t sum)
+{
+	int i;
+
+	for (i = 0; i < (len & ~1U); i += 2) {
+		sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
+		if (sum > 0xffff)
+			sum -= 0xffff;
+	}
+
+	if (i < len) {
+		sum += buf[i] << 8;
+		if (sum > 0xffff)
+			sum -= 0xffff;
+	}
+
+	return sum;
+}
+
+static uint16_t udp_checksum(struct ip *iphdr, struct udphdr *udphdr)
+{
+	uint32_t sum = 0;
+
+	sum = raw_checksum((uint8_t *)&iphdr->ip_src, 2 * sizeof(iphdr->ip_src),
+				IPPROTO_UDP + (uint32_t)(UDP_HLEN + msg_len));
+	sum = raw_checksum((uint8_t *)udp_payload, msg_len, sum);
+	sum = raw_checksum((uint8_t *)udphdr, UDP_HLEN, sum);
+	return htons(0xffff & ~sum);
+}
+
+static void send_fragment(int fd_raw, struct sockaddr *addr, socklen_t alen,
+				struct ip *iphdr, int offset)
+{
+	int frag_len;
+	int res;
+
+	if (msg_len - offset <= max_frag_len) {
+		/* This is the last fragment. */
+		frag_len = IP4_HLEN + msg_len - offset;
+		iphdr->ip_off = htons((offset + UDP_HLEN) / 8);
+	} else {
+		frag_len = IP4_HLEN + max_frag_len;
+		iphdr->ip_off = htons((offset + UDP_HLEN) / 8 | IP4_MF);
+	}
+	iphdr->ip_len = htons(frag_len);
+	memcpy(ip_frame + IP4_HLEN, udp_payload + offset,
+		 frag_len - IP4_HLEN);
+
+	res = sendto(fd_raw, ip_frame, frag_len, 0, addr, alen);
+	if (res < 0)
+		error(1, errno, "send_fragment");
+	if (res != frag_len)
+		error(1, 0, "send_fragment: %d vs %d", res, frag_len);
+
+	frag_counter++;
+}
+
+static void send_udp_frags_v4(int fd_raw, struct sockaddr *addr, socklen_t alen)
+{
+	struct ip *iphdr = (struct ip *)ip_frame;
+	struct udphdr udphdr;
+	int res;
+	int offset;
+	int frag_len;
+
+	/* Send the UDP datagram using raw IP fragments: the 0th fragment
+	 * has the UDP header; other fragments are pieces of udp_payload
+	 * split in chunks of frag_len size.
+	 *
+	 * Odd fragments (1st, 3rd, 5th, etc.) are sent out first, then
+	 * even fragments (0th, 2nd, etc.) are sent out.
+	 */
+	memset(iphdr, 0, sizeof(*iphdr));
+	iphdr->ip_hl = 5;
+	iphdr->ip_v = 4;
+	iphdr->ip_tos = 0;
+	iphdr->ip_id = htons(ip_id++);
+	iphdr->ip_ttl = 0x40;
+	iphdr->ip_p = IPPROTO_UDP;
+	iphdr->ip_src.s_addr = htonl(INADDR_LOOPBACK);
+	iphdr->ip_dst = addr4;
+	iphdr->ip_sum = 0;
+
+	/* Odd fragments. */
+	offset = 0;
+	while (offset < msg_len) {
+		send_fragment(fd_raw, addr, alen, iphdr, offset);
+		offset += 2 * max_frag_len;
+	}
+
+	if (cfg_overlap) {
+		/* Send an extra random fragment. */
+		offset = rand() % (UDP_HLEN + msg_len - 1);
+		/* sendto() returns EINVAL if offset + frag_len is too small. */
+		frag_len = IP4_HLEN + UDP_HLEN + rand() % 256;
+		iphdr->ip_off = htons(offset / 8 | IP4_MF);
+		iphdr->ip_len = htons(frag_len);
+		res = sendto(fd_raw, ip_frame, frag_len, 0, addr, alen);
+		if (res < 0)
+			error(1, errno, "sendto overlap");
+		if (res != frag_len)
+			error(1, 0, "sendto overlap: %d vs %d", (int)res, frag_len);
+		frag_counter++;
+	}
+
+	/* Zeroth fragment (UDP header). */
+	frag_len = IP4_HLEN + UDP_HLEN;
+	iphdr->ip_len = htons(frag_len);
+	iphdr->ip_off = htons(IP4_MF);
+
+	udphdr.source = htons(cfg_port + 1);
+	udphdr.dest = htons(cfg_port);
+	udphdr.len = htons(UDP_HLEN + msg_len);
+	udphdr.check = 0;
+	udphdr.check = udp_checksum(iphdr, &udphdr);
+
+	memcpy(ip_frame + IP4_HLEN, &udphdr, UDP_HLEN);
+	res = sendto(fd_raw, ip_frame, frag_len, 0, addr, alen);
+	if (res < 0)
+		error(1, errno, "sendto UDP header");
+	if (res != frag_len)
+		error(1, 0, "sendto UDP header: %d vs %d", (int)res, frag_len);
+	frag_counter++;
+
+	/* Even fragments. */
+	offset = max_frag_len;
+	while (offset < msg_len) {
+		send_fragment(fd_raw, addr, alen, iphdr, offset);
+		offset += 2 * max_frag_len;
+	}
+}
+
+static void run_test(struct sockaddr *addr, socklen_t alen)
+{
+	int fd_tx_udp, fd_tx_raw, fd_rx_udp;
+	struct timeval tv = { .tv_sec = 0, .tv_usec = 10 * 1000 };
+	int idx;
+
+	/* Initialize the payload. */
+	for (idx = 0; idx < MSG_LEN_MAX; ++idx)
+		udp_payload[idx] = idx % 256;
+
+	/* Open sockets. */
+	fd_tx_udp = socket(addr->sa_family, SOCK_DGRAM, 0);
+	if (fd_tx_udp == -1)
+		error(1, errno, "socket tx_udp");
+
+	fd_tx_raw = socket(addr->sa_family, SOCK_RAW, IPPROTO_RAW);
+	if (fd_tx_raw == -1)
+		error(1, errno, "socket tx_raw");
+
+	fd_rx_udp = socket(addr->sa_family, SOCK_DGRAM, 0);
+	if (fd_rx_udp == -1)
+		error(1, errno, "socket rx_udp");
+	if (bind(fd_rx_udp, addr, alen))
+		error(1, errno, "bind");
+	/* Fail fast. */
+	if (setsockopt(fd_rx_udp, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
+		error(1, errno, "setsockopt rcv timeout");
+
+	for (msg_len = 1; msg_len < MSG_LEN_MAX; msg_len += (rand() % 4096)) {
+		if (cfg_verbose)
+			printf("msg_len: %d\n", msg_len);
+		max_frag_len = addr->sa_family == AF_INET ? 8 : 1280;
+		for (; max_frag_len < 1500 && max_frag_len <= msg_len;
+				max_frag_len += 8) {
+			send_udp_frags_v4(fd_tx_raw, addr, alen);
+			recv_validate_udp(fd_rx_udp);
+		}
+	}
+
+	/* Cleanup. */
+	if (close(fd_tx_raw))
+		error(1, errno, "close tx_raw");
+	if (close(fd_tx_udp))
+		error(1, errno, "close tx_udp");
+	if (close(fd_rx_udp))
+		error(1, errno, "close rx_udp");
+
+	if (cfg_verbose)
+		printf("processed %d messages, %d fragments\n",
+			msg_counter, frag_counter);
+
+	fprintf(stderr, "PASS\n");
+}
+
+
+static void run_test_v4(void)
+{
+	struct sockaddr_in addr = {0};
+
+	addr.sin_family = AF_INET;
+	addr.sin_port = htons(cfg_port);
+	addr.sin_addr = addr4;
+
+	run_test((void *)&addr, sizeof(addr));
+}
+
+static void run_test_v6(void)
+{
+	fprintf(stderr, "NOT IMPL.\n");
+	exit(1);
+}
+
+static void parse_opts(int argc, char **argv)
+{
+	int c;
+
+	while ((c = getopt(argc, argv, "46ov")) != -1) {
+		switch (c) {
+		case '4':
+			cfg_do_ipv4 = true;
+			break;
+		case '6':
+			cfg_do_ipv6 = true;
+			break;
+		case 'o':
+			cfg_overlap = true;
+			break;
+		case 'v':
+			cfg_verbose = true;
+			break;
+		default:
+			error(1, 0, "%s: parse error", argv[0]);
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	parse_opts(argc, argv);
+	seed = time(NULL);
+	srand(seed);
+
+	if (cfg_do_ipv4)
+		run_test_v4();
+	if (cfg_do_ipv6)
+		run_test_v6();
+
+	return 0;
+}
diff --git a/tools/testing/selftests/net/ip_defrag.sh b/tools/testing/selftests/net/ip_defrag.sh
new file mode 100755
index 000000000000..53a1ed46790d
--- /dev/null
+++ b/tools/testing/selftests/net/ip_defrag.sh
@@ -0,0 +1,29 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Run a couple of IP defragmentation tests.
+
+set +x
+set -e
+
+echo "ipv4 defrag"
+
+run_v4() {
+sysctl -w net.ipv4.ipfrag_high_thresh=9000000 &> /dev/null
+sysctl -w net.ipv4.ipfrag_low_thresh=7000000 &> /dev/null
+./ip_defrag -4
+}
+export -f run_v4
+
+./in_netns.sh "run_v4"
+
+echo "ipv4 defrag with overlaps"
+run_v4o() {
+sysctl -w net.ipv4.ipfrag_high_thresh=9000000 &> /dev/null
+sysctl -w net.ipv4.ipfrag_low_thresh=7000000 &> /dev/null
+./ip_defrag -4o
+}
+export -f run_v4o
+
+./in_netns.sh "run_v4o"
+
-- 
2.19.0.rc0.228.g281dcd1b4d0-goog

Re: [PATCH net-next 1/2] ip: fail fast on IP defrag errors

[David Miller]

From: Peter Oskolkov <posk@google.com>
Date: Tue, 28 Aug 2018 11:36:19 -0700

> The current behavior of IP defragmentation is inconsistent:
> - some overlapping/wrong length fragments are dropped without
>   affecting the queue;
> - most overlapping fragments cause the whole frag queue to be dropped.
> 
> This patch brings consistency: if a bad fragment is detected,
> the whole frag queue is dropped. Two major benefits:
> - fail fast: corrupted frag queues are cleared immediately, instead of
>   by timeout;
> - testing of overlapping fragments is now much easier: any kind of
>   random fragment length mutation now leads to the frag queue being
>   discarded (IP packet dropped); before this patch, some overlaps were
>   "corrected", with tests not seeing expected packet drops.
> 
> Note that in one case (see "if (end&7)" conditional) the current
> behavior is preserved as there are concerns that this could be
> legitimate padding.
> 
> Signed-off-by: Peter Oskolkov <posk@google.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Reviewed-by: Willem de Bruijn <willemb@google.com>

Applied.

Re: [PATCH net-next 2/2] selftests/net: add ip_defrag selftest

[David Miller]

From: Peter Oskolkov <posk@google.com>
Date: Tue, 28 Aug 2018 11:36:20 -0700

> This test creates a raw IPv4 socket, fragments a largish UDP
> datagram and sends the fragments out of order.
> 
> Then repeats in a loop with different message and fragment lengths.
> 
> Then does the same with overlapping fragments (with overlapping
> fragments the expectation is that the recv times out).
> 
> Tested:
> 
> root@<host># time ./ip_defrag.sh
> ipv4 defrag
> PASS
> ipv4 defrag with overlaps
> PASS
> 
> real    1m7.679s
> user    0m0.628s
> sys     0m2.242s
> 
> A similar test for IPv6 is to follow.
> 
> Signed-off-by: Peter Oskolkov <posk@google.com>
> Reviewed-by: Willem de Bruijn <willemb@google.com>

Applied.