From d4bac0288a2b444e468e6df9cb4ed69479ddf14a Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Tue, 8 Apr 2025 09:27:48 -0400 Subject: bpf: support SKF_NET_OFF and SKF_LL_OFF on skb frags MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Classic BPF socket filters with SKB_NET_OFF and SKB_LL_OFF fail to read when these offsets extend into frags. This has been observed with iwlwifi and reproduced with tun with IFF_NAPI_FRAGS. The below straightforward socket filter on UDP port, applied to a RAW socket, will silently miss matching packets. const int offset_proto = offsetof(struct ip6_hdr, ip6_nxt); const int offset_dport = sizeof(struct ip6_hdr) + offsetof(struct udphdr, dest); struct sock_filter filter_code[] = { BPF_STMT(BPF_LD + BPF_B + BPF_ABS, SKF_AD_OFF + SKF_AD_PKTTYPE), BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, PACKET_HOST, 0, 4), BPF_STMT(BPF_LD + BPF_B + BPF_ABS, SKF_NET_OFF + offset_proto), BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 2), BPF_STMT(BPF_LD + BPF_H + BPF_ABS, SKF_NET_OFF + offset_dport), This is unexpected behavior. Socket filter programs should be consistent regardless of environment. Silent misses are particularly concerning as hard to detect. Use skb_copy_bits for offsets outside linear, same as done for non-SKF_(LL|NET) offsets. Offset is always positive after subtracting the reference threshold SKB_(LL|NET)_OFF, so is always >= skb_(mac|network)_offset. The sum of the two is an offset against skb->data, and may be negative, but it cannot point before skb->head, as skb_(mac|network)_offset would too. This appears to go back to when frag support was introduced to sk_run_filter in linux-2.4.4, before the introduction of git. The amount of code change and 8/16/32 bit duplication are unfortunate. But any attempt I made to be smarter saved very few LoC while complicating the code. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Link: https://lore.kernel.org/netdev/20250122200402.3461154-1-maze@google.com/ Link: https://elixir.bootlin.com/linux/2.4.4/source/net/core/filter.c#L244 Reported-by: Matt Moeller Co-developed-by: Maciej Żenczykowski Signed-off-by: Maciej Żenczykowski Signed-off-by: Willem de Bruijn Acked-by: Stanislav Fomichev Link: https://lore.kernel.org/r/20250408132833.195491-2-willemdebruijn.kernel@gmail.com Signed-off-by: Alexei Starovoitov --- net/core/filter.c | 80 ++++++++++++++++++++++++++++++------------------------- 1 file changed, 44 insertions(+), 36 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index bc6828761a47..79cab4d78dc3 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -218,24 +218,36 @@ BPF_CALL_3(bpf_skb_get_nlattr_nest, struct sk_buff *, skb, u32, a, u32, x) return 0; } +static int bpf_skb_load_helper_convert_offset(const struct sk_buff *skb, int offset) +{ + if (likely(offset >= 0)) + return offset; + + if (offset >= SKF_NET_OFF) + return offset - SKF_NET_OFF + skb_network_offset(skb); + + if (offset >= SKF_LL_OFF && skb_mac_header_was_set(skb)) + return offset - SKF_LL_OFF + skb_mac_offset(skb); + + return INT_MIN; +} + BPF_CALL_4(bpf_skb_load_helper_8, const struct sk_buff *, skb, const void *, data, int, headlen, int, offset) { - u8 tmp, *ptr; + u8 tmp; const int len = sizeof(tmp); - if (offset >= 0) { - if (headlen - offset >= len) - return *(u8 *)(data + offset); - if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) - return tmp; - } else { - ptr = bpf_internal_load_pointer_neg_helper(skb, offset, len); - if (likely(ptr)) - return *(u8 *)ptr; - } + offset = bpf_skb_load_helper_convert_offset(skb, offset); + if (offset == INT_MIN) + return -EFAULT; - return -EFAULT; + if (headlen - offset >= len) + return *(u8 *)(data + offset); + if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) + return tmp; + else + return -EFAULT; } BPF_CALL_2(bpf_skb_load_helper_8_no_cache, const struct sk_buff *, skb, @@ -248,21 +260,19 @@ BPF_CALL_2(bpf_skb_load_helper_8_no_cache, const struct sk_buff *, skb, BPF_CALL_4(bpf_skb_load_helper_16, const struct sk_buff *, skb, const void *, data, int, headlen, int, offset) { - __be16 tmp, *ptr; + __be16 tmp; const int len = sizeof(tmp); - if (offset >= 0) { - if (headlen - offset >= len) - return get_unaligned_be16(data + offset); - if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) - return be16_to_cpu(tmp); - } else { - ptr = bpf_internal_load_pointer_neg_helper(skb, offset, len); - if (likely(ptr)) - return get_unaligned_be16(ptr); - } + offset = bpf_skb_load_helper_convert_offset(skb, offset); + if (offset == INT_MIN) + return -EFAULT; - return -EFAULT; + if (headlen - offset >= len) + return get_unaligned_be16(data + offset); + if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) + return be16_to_cpu(tmp); + else + return -EFAULT; } BPF_CALL_2(bpf_skb_load_helper_16_no_cache, const struct sk_buff *, skb, @@ -275,21 +285,19 @@ BPF_CALL_2(bpf_skb_load_helper_16_no_cache, const struct sk_buff *, skb, BPF_CALL_4(bpf_skb_load_helper_32, const struct sk_buff *, skb, const void *, data, int, headlen, int, offset) { - __be32 tmp, *ptr; + __be32 tmp; const int len = sizeof(tmp); - if (likely(offset >= 0)) { - if (headlen - offset >= len) - return get_unaligned_be32(data + offset); - if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) - return be32_to_cpu(tmp); - } else { - ptr = bpf_internal_load_pointer_neg_helper(skb, offset, len); - if (likely(ptr)) - return get_unaligned_be32(ptr); - } + offset = bpf_skb_load_helper_convert_offset(skb, offset); + if (offset == INT_MIN) + return -EFAULT; - return -EFAULT; + if (headlen - offset >= len) + return get_unaligned_be32(data + offset); + if (!skb_copy_bits(skb, offset, &tmp, sizeof(tmp))) + return be32_to_cpu(tmp); + else + return -EFAULT; } BPF_CALL_2(bpf_skb_load_helper_32_no_cache, const struct sk_buff *, skb, -- cgit From fcd7132cb1f93e4d4594ecb19b8dcecdf0497d9e Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Tue, 8 Apr 2025 09:27:49 -0400 Subject: selftests/net: test sk_filter support for SKF_NET_OFF on frags Verify that a classic BPF linux socket filter correctly matches packet contents. Including when accessing contents in an skb_frag. 1. Open a SOCK_RAW socket with a classic BPF filter on UDP dport 8000. 2. Open a tap device with IFF_NAPI_FRAGS to inject skbs with frags. 3. Send a packet for which the UDP header is in frag[0]. 4. Receive this packet to demonstrate that the socket accepted it. Acked-by: Stanislav Fomichev Signed-off-by: Willem de Bruijn Link: https://lore.kernel.org/r/20250408132833.195491-3-willemdebruijn.kernel@gmail.com Signed-off-by: Alexei Starovoitov --- tools/testing/selftests/net/.gitignore | 1 + tools/testing/selftests/net/Makefile | 2 + tools/testing/selftests/net/skf_net_off.c | 244 +++++++++++++++++++++++++++++ tools/testing/selftests/net/skf_net_off.sh | 30 ++++ 4 files changed, 277 insertions(+) create mode 100644 tools/testing/selftests/net/skf_net_off.c create mode 100755 tools/testing/selftests/net/skf_net_off.sh diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore index 679542f565a4..532bb732bc6d 100644 --- a/tools/testing/selftests/net/.gitignore +++ b/tools/testing/selftests/net/.gitignore @@ -39,6 +39,7 @@ scm_rights sk_bind_sendto_listen sk_connect_zero_addr sk_so_peek_off +skf_net_off socket so_incoming_cpu so_netns_cookie diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile index 6d718b478ed8..124078b56fa4 100644 --- a/tools/testing/selftests/net/Makefile +++ b/tools/testing/selftests/net/Makefile @@ -106,6 +106,8 @@ TEST_PROGS += ipv6_route_update_soft_lockup.sh TEST_PROGS += busy_poll_test.sh TEST_GEN_PROGS += proc_net_pktgen TEST_PROGS += lwt_dst_cache_ref_loop.sh +TEST_PROGS += skf_net_off.sh +TEST_GEN_FILES += skf_net_off # YNL files, must be before "include ..lib.mk" YNL_GEN_FILES := busy_poller netlink-dumps diff --git a/tools/testing/selftests/net/skf_net_off.c b/tools/testing/selftests/net/skf_net_off.c new file mode 100644 index 000000000000..1fdf61d6cd7f --- /dev/null +++ b/tools/testing/selftests/net/skf_net_off.c @@ -0,0 +1,244 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* Open a tun device. + * + * [modifications: use IFF_NAPI_FRAGS, add sk filter] + * + * Expects the device to have been configured previously, e.g.: + * sudo ip tuntap add name tap1 mode tap + * sudo ip link set tap1 up + * sudo ip link set dev tap1 addr 02:00:00:00:00:01 + * sudo ip -6 addr add fdab::1 peer fdab::2 dev tap1 nodad + * + * And to avoid premature pskb_may_pull: + * + * sudo ethtool -K tap1 gro off + * sudo bash -c 'echo 0 > /proc/sys/net/ipv4/ip_early_demux' + */ + +#define _GNU_SOURCE + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +static bool cfg_do_filter; +static bool cfg_do_frags; +static int cfg_dst_port = 8000; +static char *cfg_ifname; + +static int tun_open(const char *tun_name) +{ + struct ifreq ifr = {0}; + int fd, ret; + + fd = open("/dev/net/tun", O_RDWR); + if (fd == -1) + error(1, errno, "open /dev/net/tun"); + + ifr.ifr_flags = IFF_TAP; + if (cfg_do_frags) + ifr.ifr_flags |= IFF_NAPI | IFF_NAPI_FRAGS; + + strncpy(ifr.ifr_name, tun_name, IFNAMSIZ - 1); + + ret = ioctl(fd, TUNSETIFF, &ifr); + if (ret) + error(1, ret, "ioctl TUNSETIFF"); + + return fd; +} + +static void sk_set_filter(int fd) +{ + const int offset_proto = offsetof(struct ip6_hdr, ip6_nxt); + const int offset_dport = sizeof(struct ip6_hdr) + offsetof(struct udphdr, dest); + + /* Filter UDP packets with destination port cfg_dst_port */ + struct sock_filter filter_code[] = { + BPF_STMT(BPF_LD + BPF_B + BPF_ABS, SKF_AD_OFF + SKF_AD_PKTTYPE), + BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, PACKET_HOST, 0, 4), + BPF_STMT(BPF_LD + BPF_B + BPF_ABS, SKF_NET_OFF + offset_proto), + BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 2), + BPF_STMT(BPF_LD + BPF_H + BPF_ABS, SKF_NET_OFF + offset_dport), + BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, cfg_dst_port, 1, 0), + BPF_STMT(BPF_RET + BPF_K, 0), + BPF_STMT(BPF_RET + BPF_K, 0xFFFF), + }; + + struct sock_fprog filter = { + sizeof(filter_code) / sizeof(filter_code[0]), + filter_code, + }; + + if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter))) + error(1, errno, "setsockopt attach filter"); +} + +static int raw_open(void) +{ + int fd; + + fd = socket(PF_INET6, SOCK_RAW, IPPROTO_UDP); + if (fd == -1) + error(1, errno, "socket raw (udp)"); + + if (cfg_do_filter) + sk_set_filter(fd); + + return fd; +} + +static void tun_write(int fd) +{ + const char eth_src[] = { 0x02, 0x00, 0x00, 0x00, 0x00, 0x02 }; + const char eth_dst[] = { 0x02, 0x00, 0x00, 0x00, 0x00, 0x01 }; + struct tun_pi pi = {0}; + struct ipv6hdr ip6h = {0}; + struct udphdr uh = {0}; + struct ethhdr eth = {0}; + uint32_t payload; + struct iovec iov[5]; + int ret; + + pi.proto = htons(ETH_P_IPV6); + + memcpy(eth.h_source, eth_src, sizeof(eth_src)); + memcpy(eth.h_dest, eth_dst, sizeof(eth_dst)); + eth.h_proto = htons(ETH_P_IPV6); + + ip6h.version = 6; + ip6h.payload_len = htons(sizeof(uh) + sizeof(uint32_t)); + ip6h.nexthdr = IPPROTO_UDP; + ip6h.hop_limit = 8; + if (inet_pton(AF_INET6, "fdab::2", &ip6h.saddr) != 1) + error(1, errno, "inet_pton src"); + if (inet_pton(AF_INET6, "fdab::1", &ip6h.daddr) != 1) + error(1, errno, "inet_pton src"); + + uh.source = htons(8000); + uh.dest = htons(cfg_dst_port); + uh.len = ip6h.payload_len; + uh.check = 0; + + payload = htonl(0xABABABAB); /* Covered in IPv6 length */ + + iov[0].iov_base = π + iov[0].iov_len = sizeof(pi); + iov[1].iov_base = ð + iov[1].iov_len = sizeof(eth); + iov[2].iov_base = &ip6h; + iov[2].iov_len = sizeof(ip6h); + iov[3].iov_base = &uh; + iov[3].iov_len = sizeof(uh); + iov[4].iov_base = &payload; + iov[4].iov_len = sizeof(payload); + + ret = writev(fd, iov, sizeof(iov) / sizeof(iov[0])); + if (ret <= 0) + error(1, errno, "writev"); +} + +static void raw_read(int fd) +{ + struct timeval tv = { .tv_usec = 100 * 1000 }; + struct msghdr msg = {0}; + struct iovec iov[2]; + struct udphdr uh; + uint32_t payload[2]; + int ret; + + if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv))) + error(1, errno, "setsockopt rcvtimeo udp"); + + iov[0].iov_base = &uh; + iov[0].iov_len = sizeof(uh); + + iov[1].iov_base = payload; + iov[1].iov_len = sizeof(payload); + + msg.msg_iov = iov; + msg.msg_iovlen = sizeof(iov) / sizeof(iov[0]); + + ret = recvmsg(fd, &msg, 0); + if (ret <= 0) + error(1, errno, "read raw"); + if (ret != sizeof(uh) + sizeof(payload[0])) + error(1, errno, "read raw: len=%d\n", ret); + + fprintf(stderr, "raw recv: 0x%x\n", payload[0]); +} + +static void parse_opts(int argc, char **argv) +{ + int c; + + while ((c = getopt(argc, argv, "fFi:")) != -1) { + switch (c) { + case 'f': + cfg_do_filter = true; + printf("bpf filter enabled\n"); + break; + case 'F': + cfg_do_frags = true; + printf("napi frags mode enabled\n"); + break; + case 'i': + cfg_ifname = optarg; + break; + default: + error(1, 0, "unknown option %c", optopt); + break; + } + } + + if (!cfg_ifname) + error(1, 0, "must specify tap interface name (-i)"); +} + +int main(int argc, char **argv) +{ + int fdt, fdr; + + parse_opts(argc, argv); + + fdr = raw_open(); + fdt = tun_open(cfg_ifname); + + tun_write(fdt); + raw_read(fdr); + + if (close(fdt)) + error(1, errno, "close tun"); + if (close(fdr)) + error(1, errno, "close udp"); + + fprintf(stderr, "OK\n"); + return 0; +} + diff --git a/tools/testing/selftests/net/skf_net_off.sh b/tools/testing/selftests/net/skf_net_off.sh new file mode 100755 index 000000000000..5da5066fb465 --- /dev/null +++ b/tools/testing/selftests/net/skf_net_off.sh @@ -0,0 +1,30 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 + +readonly NS="ns-$(mktemp -u XXXXXX)" + +cleanup() { + ip netns del $NS +} + +ip netns add $NS +trap cleanup EXIT + +ip -netns $NS link set lo up +ip -netns $NS tuntap add name tap1 mode tap +ip -netns $NS link set tap1 up +ip -netns $NS link set dev tap1 addr 02:00:00:00:00:01 +ip -netns $NS -6 addr add fdab::1 peer fdab::2 dev tap1 nodad +ip netns exec $NS ethtool -K tap1 gro off + +# disable early demux, else udp_v6_early_demux pulls udp header into linear +ip netns exec $NS sysctl -w net.ipv4.ip_early_demux=0 + +echo "no filter" +ip netns exec $NS ./skf_net_off -i tap1 + +echo "filter, linear skb (-f)" +ip netns exec $NS ./skf_net_off -i tap1 -f + +echo "filter, fragmented skb (-f) (-F)" +ip netns exec $NS ./skf_net_off -i tap1 -f -F -- cgit