[PATCH bpf 0/2] bpf: Derive source IP addr via bpf_*_fib_lookup()

[PATCH bpf 0/2] bpf: Derive source IP addr via bpf_*_fib_lookup()

[Martynas Pumputis]

The patchset fixes the limitation of bpf_*_fib_lookup() helper, which
prevents it from being used in BPF dataplanes with network interfaces
which have more than one IP addr. See the first patch for more details.
Thanks!

Martynas Pumputis (2):
  bpf: Derive source IP addr via bpf_*_fib_lookup()
  selftests/bpf: Add BPF_FIB_LOOKUP_SET_SRC tests

 include/uapi/linux/bpf.h                      |  9 +++
 net/core/filter.c                             | 13 +++-
 tools/include/uapi/linux/bpf.h                | 10 +++
 .../selftests/bpf/prog_tests/fib_lookup.c     | 76 +++++++++++++++++--
 4 files changed, 101 insertions(+), 7 deletions(-)

-- 
2.42.0

[PATCH bpf 1/2] bpf: Derive source IP addr via bpf_*_fib_lookup()

[Martynas Pumputis]

Extend the bpf_fib_lookup() helper by making it to return the source
IPv4/IPv6 address if the BPF_FIB_LOOKUP_SET_SRC flag is set.

For example, the following snippet can be used to derive the desired
source IP address:

    struct bpf_fib_lookup p = { .ipv4_dst = ip4->daddr };

    ret = bpf_skb_fib_lookup(skb, p, sizeof(p),
            BPF_FIB_LOOKUP_SET_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH);
    if (ret != BPF_FIB_LKUP_RET_SUCCESS)
        return TC_ACT_SHOT;

    /* the p.ipv4_src now contains the source address */

The inability to derive the proper source address may cause malfunctions
in BPF-based dataplanes for hosts containing netdevs with more than one
routable IP address or for multi-homed hosts.

For example, Cilium implements packet masquerading in BPF. If an
egressing netdev to which the Cilium's BPF prog is attached has
multiple IP addresses, then only one [hardcoded] IP address can be used for
masquerading. This breaks connectivity if any other IP address should have
been selected instead, for example, when a public and private addresses
are attached to the same egress interface.

The change was tested with Cilium [1].

Nikolay Aleksandrov helped to figure out the IPv6 addr selection.

[1]: https://github.com/cilium/cilium/pull/28283

Signed-off-by: Martynas Pumputis <m@lambda.lt>
---
 include/uapi/linux/bpf.h       |  9 +++++++++
 net/core/filter.c              | 13 ++++++++++++-
 tools/include/uapi/linux/bpf.h | 10 ++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0448700890f7..a6bf686eecbc 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3257,6 +3257,10 @@ union bpf_attr {
  *			and *params*->smac will not be set as output. A common
  *			use case is to call **bpf_redirect_neigh**\ () after
  *			doing **bpf_fib_lookup**\ ().
+ *		**BPF_FIB_LOOKUP_SET_SRC**
+ *			Derive and set source IP addr in *params*->ipv{4,6}_src
+ *			for the nexthop. If the src addr cannot be derived,
+ *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned.
  *
  *		*ctx* is either **struct xdp_md** for XDP programs or
  *		**struct sk_buff** tc cls_act programs.
@@ -6953,6 +6957,7 @@ enum {
 	BPF_FIB_LOOKUP_OUTPUT  = (1U << 1),
 	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
 	BPF_FIB_LOOKUP_TBID    = (1U << 3),
+	BPF_FIB_LOOKUP_SET_SRC = (1U << 4),
 };
 
 enum {
@@ -6965,6 +6970,7 @@ enum {
 	BPF_FIB_LKUP_RET_UNSUPP_LWT,   /* fwd requires encapsulation */
 	BPF_FIB_LKUP_RET_NO_NEIGH,     /* no neighbor entry for nh */
 	BPF_FIB_LKUP_RET_FRAG_NEEDED,  /* fragmentation required to fwd */
+	BPF_FIB_LKUP_RET_NO_SRC_ADDR,  /* failed to derive IP src addr */
 };
 
 struct bpf_fib_lookup {
@@ -6999,6 +7005,9 @@ struct bpf_fib_lookup {
 		__u32	rt_metric;
 	};
 
+	/* input: source address to consider for lookup
+	 * output: source address result from lookup
+	 */
 	union {
 		__be32		ipv4_src;
 		__u32		ipv6_src[4];  /* in6_addr; network order */
diff --git a/net/core/filter.c b/net/core/filter.c
index a094694899c9..e9cdcf49df62 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5850,6 +5850,9 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 	params->rt_metric = res.fi->fib_priority;
 	params->ifindex = dev->ifindex;
 
+	if (flags & BPF_FIB_LOOKUP_SET_SRC)
+		params->ipv4_src = fib_result_prefsrc(net, &res);
+
 	/* xdp and cls_bpf programs are run in RCU-bh so
 	 * rcu_read_lock_bh is not needed here
 	 */
@@ -5992,6 +5995,13 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 	params->rt_metric = res.f6i->fib6_metric;
 	params->ifindex = dev->ifindex;
 
+	if (flags & BPF_FIB_LOOKUP_SET_SRC) {
+		err = ip6_route_get_saddr(net, res.f6i, &fl6.daddr, 0,
+					  (struct in6_addr *)&params->ipv6_src);
+		if (err)
+			return BPF_FIB_LKUP_RET_NO_SRC_ADDR;
+	}
+
 	if (flags & BPF_FIB_LOOKUP_SKIP_NEIGH)
 		goto set_fwd_params;
 
@@ -6010,7 +6020,8 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 #endif
 
 #define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \
-			     BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID)
+			     BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID | \
+			     BPF_FIB_LOOKUP_SET_SRC)
 
 BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
 	   struct bpf_fib_lookup *, params, int, plen, u32, flags)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 0448700890f7..72cd0ca97689 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3257,6 +3257,10 @@ union bpf_attr {
  *			and *params*->smac will not be set as output. A common
  *			use case is to call **bpf_redirect_neigh**\ () after
  *			doing **bpf_fib_lookup**\ ().
+ *		**BPF_FIB_LOOKUP_SET_SRC**
+ *			Derive and set source IP addr in *params*->ipv{4,6}_src
+ *			for the nexthop. If the src addr cannot be derived,
+ *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned.
  *
  *		*ctx* is either **struct xdp_md** for XDP programs or
  *		**struct sk_buff** tc cls_act programs.
@@ -6953,6 +6957,7 @@ enum {
 	BPF_FIB_LOOKUP_OUTPUT  = (1U << 1),
 	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
 	BPF_FIB_LOOKUP_TBID    = (1U << 3),
+	BPF_FIB_LOOKUP_SET_SRC = (1U << 4),
 };
 
 enum {
@@ -6965,6 +6970,7 @@ enum {
 	BPF_FIB_LKUP_RET_UNSUPP_LWT,   /* fwd requires encapsulation */
 	BPF_FIB_LKUP_RET_NO_NEIGH,     /* no neighbor entry for nh */
 	BPF_FIB_LKUP_RET_FRAG_NEEDED,  /* fragmentation required to fwd */
+	BPF_FIB_LKUP_RET_NO_SRC_ADDR,  /* failed to derive IP src addr */
 };
 
 struct bpf_fib_lookup {
@@ -6999,6 +7005,10 @@ struct bpf_fib_lookup {
 		__u32	rt_metric;
 	};
 
+
+	/* input: source address to consider for lookup
+	 * output: source address result from lookup
+	 */
 	union {
 		__be32		ipv4_src;
 		__u32		ipv6_src[4];  /* in6_addr; network order */
-- 
2.42.0

Re: [PATCH bpf 1/2] bpf: Derive source IP addr via bpf_*_fib_lookup()

[kernel test robot]

Hi Martynas,

kernel test robot noticed the following build errors:

[auto build test ERROR on bpf/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Martynas-Pumputis/bpf-Derive-source-IP-addr-via-bpf_-_fib_lookup/20230929-231536
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
patch link:    https://lore.kernel.org/r/20230929150717.120463-2-m%40lambda.lt
patch subject: [PATCH bpf 1/2] bpf: Derive source IP addr via bpf_*_fib_lookup()
config: i386-buildonly-randconfig-006-20230930 (https://download.01.org/0day-ci/archive/20230930/202309302249.FeC1Gbp9-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230930/202309302249.FeC1Gbp9-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309302249.FeC1Gbp9-lkp@intel.com/

All errors (new ones prefixed by >>):

   ld: net/core/filter.o: in function `ip6_route_get_saddr.constprop.0':
>> filter.c:(.text+0xaebe): undefined reference to `ipv6_dev_get_saddr'

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH bpf 1/2] bpf: Derive source IP addr via bpf_*_fib_lookup()

[kernel test robot]

Hi Martynas,

kernel test robot noticed the following build errors:

[auto build test ERROR on bpf/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Martynas-Pumputis/bpf-Derive-source-IP-addr-via-bpf_-_fib_lookup/20230929-231536
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
patch link:    https://lore.kernel.org/r/20230929150717.120463-2-m%40lambda.lt
patch subject: [PATCH bpf 1/2] bpf: Derive source IP addr via bpf_*_fib_lookup()
config: csky-allmodconfig (https://download.01.org/0day-ci/archive/20231001/202310011747.2WjYkVa8-lkp@intel.com/config)
compiler: csky-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231001/202310011747.2WjYkVa8-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202310011747.2WjYkVa8-lkp@intel.com/

All errors (new ones prefixed by >>):

   csky-linux-ld: net/core/filter.o: in function `ip6_route_get_saddr.constprop.0':
   filter.c:(.text+0x7594): undefined reference to `ipv6_dev_get_saddr'
>> csky-linux-ld: filter.c:(.text+0x75c0): undefined reference to `ipv6_dev_get_saddr'

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH bpf 2/2] selftests/bpf: Add BPF_FIB_LOOKUP_SET_SRC tests

[Martynas Pumputis]

This patch extends the existing fib_lookup test suite by adding two test
cases (for each IP family):

* Test source IP selection when default route is used.
* Test source IP selection when an IP route has a preferred src IP addr.

Signed-off-by: Martynas Pumputis <m@lambda.lt>
---
 .../selftests/bpf/prog_tests/fib_lookup.c     | 76 +++++++++++++++++--
 1 file changed, 70 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/fib_lookup.c b/tools/testing/selftests/bpf/prog_tests/fib_lookup.c
index 2fd05649bad1..1b0ab1dbd4f1 100644
--- a/tools/testing/selftests/bpf/prog_tests/fib_lookup.c
+++ b/tools/testing/selftests/bpf/prog_tests/fib_lookup.c
@@ -11,9 +11,13 @@
 
 #define NS_TEST			"fib_lookup_ns"
 #define IPV6_IFACE_ADDR		"face::face"
+#define IPV6_IFACE_ADDR_SEC	"cafe::cafe"
+#define IPV6_ADDR_DST		"face::3"
 #define IPV6_NUD_FAILED_ADDR	"face::1"
 #define IPV6_NUD_STALE_ADDR	"face::2"
 #define IPV4_IFACE_ADDR		"10.0.0.254"
+#define IPV4_IFACE_ADDR_SEC	"10.1.0.254"
+#define IPV4_ADDR_DST		"10.2.0.254"
 #define IPV4_NUD_FAILED_ADDR	"10.0.0.1"
 #define IPV4_NUD_STALE_ADDR	"10.0.0.2"
 #define IPV4_TBID_ADDR		"172.0.0.254"
@@ -31,6 +35,8 @@ struct fib_lookup_test {
 	const char *desc;
 	const char *daddr;
 	int expected_ret;
+	const char *expected_ipv4_src;
+	const char *expected_ipv6_src;
 	int lookup_flags;
 	__u32 tbid;
 	__u8 dmac[6];
@@ -69,6 +75,22 @@ static const struct fib_lookup_test tests[] = {
 	  .daddr = IPV6_TBID_DST, .expected_ret = BPF_FIB_LKUP_RET_SUCCESS,
 	  .lookup_flags = BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_TBID, .tbid = 100,
 	  .dmac = DMAC_INIT2, },
+	{ .desc = "IPv4 set src addr",
+	  .daddr = IPV4_NUD_FAILED_ADDR, .expected_ret = BPF_FIB_LKUP_RET_SUCCESS,
+	  .expected_ipv4_src = IPV4_IFACE_ADDR,
+	  .lookup_flags = BPF_FIB_LOOKUP_SET_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH, },
+	{ .desc = "IPv6 set src addr",
+	  .daddr = IPV6_NUD_FAILED_ADDR, .expected_ret = BPF_FIB_LKUP_RET_SUCCESS,
+	  .expected_ipv6_src = IPV6_IFACE_ADDR,
+	  .lookup_flags = BPF_FIB_LOOKUP_SET_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH, },
+	{ .desc = "IPv4 set prefsrc addr from route",
+	  .daddr = IPV4_ADDR_DST, .expected_ret = BPF_FIB_LKUP_RET_SUCCESS,
+	  .expected_ipv4_src = IPV4_IFACE_ADDR_SEC,
+	  .lookup_flags = BPF_FIB_LOOKUP_SET_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH, },
+	{ .desc = "IPv6 set prefsrc addr route",
+	  .daddr = IPV6_ADDR_DST, .expected_ret = BPF_FIB_LKUP_RET_SUCCESS,
+	  .expected_ipv6_src = IPV6_IFACE_ADDR_SEC,
+	  .lookup_flags = BPF_FIB_LOOKUP_SET_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH, },
 };
 
 static int ifindex;
@@ -97,6 +119,13 @@ static int setup_netns(void)
 	SYS(fail, "ip neigh add %s dev veth1 nud failed", IPV4_NUD_FAILED_ADDR);
 	SYS(fail, "ip neigh add %s dev veth1 lladdr %s nud stale", IPV4_NUD_STALE_ADDR, DMAC);
 
+	/* Setup for prefsrc IP addr selection */
+	SYS(fail, "ip addr add %s/24 dev veth1", IPV4_IFACE_ADDR_SEC);
+	SYS(fail, "ip route add %s/32 dev veth1 src %s", IPV4_ADDR_DST, IPV4_IFACE_ADDR_SEC);
+
+	SYS(fail, "ip addr add %s/64 dev veth1 nodad", IPV6_IFACE_ADDR_SEC);
+	SYS(fail, "ip route add %s/128 dev veth1 src %s", IPV6_ADDR_DST, IPV6_IFACE_ADDR_SEC);
+
 	/* Setup for tbid lookup tests */
 	SYS(fail, "ip addr add %s/24 dev veth2", IPV4_TBID_ADDR);
 	SYS(fail, "ip route del %s/24 dev veth2", IPV4_TBID_NET);
@@ -133,9 +162,12 @@ static int set_lookup_params(struct bpf_fib_lookup *params, const struct fib_loo
 
 	if (inet_pton(AF_INET6, test->daddr, params->ipv6_dst) == 1) {
 		params->family = AF_INET6;
-		ret = inet_pton(AF_INET6, IPV6_IFACE_ADDR, params->ipv6_src);
-		if (!ASSERT_EQ(ret, 1, "inet_pton(IPV6_IFACE_ADDR)"))
-			return -1;
+		if (!(test->lookup_flags & BPF_FIB_LOOKUP_SET_SRC)) {
+			ret = inet_pton(AF_INET6, IPV6_IFACE_ADDR, params->ipv6_src);
+			if (!ASSERT_EQ(ret, 1, "inet_pton(IPV6_IFACE_ADDR)"))
+				return -1;
+		}
+
 		return 0;
 	}
 
@@ -143,9 +175,12 @@ static int set_lookup_params(struct bpf_fib_lookup *params, const struct fib_loo
 	if (!ASSERT_EQ(ret, 1, "convert IP[46] address"))
 		return -1;
 	params->family = AF_INET;
-	ret = inet_pton(AF_INET, IPV4_IFACE_ADDR, &params->ipv4_src);
-	if (!ASSERT_EQ(ret, 1, "inet_pton(IPV4_IFACE_ADDR)"))
-		return -1;
+
+	if (!(test->lookup_flags & BPF_FIB_LOOKUP_SET_SRC)) {
+		ret = inet_pton(AF_INET, IPV4_IFACE_ADDR, &params->ipv4_src);
+		if (!ASSERT_EQ(ret, 1, "inet_pton(IPV4_IFACE_ADDR)"))
+			return -1;
+	}
 
 	return 0;
 }
@@ -207,6 +242,35 @@ void test_fib_lookup(void)
 		ASSERT_EQ(skel->bss->fib_lookup_ret, tests[i].expected_ret,
 			  "fib_lookup_ret");
 
+		if (tests[i].expected_ipv4_src) {
+			__be32 expected_ipv4_src;
+
+			ret = inet_pton(AF_INET, tests[i].expected_ipv4_src,
+					&expected_ipv4_src);
+			ASSERT_EQ(ret, 1, "inet_pton(expected_ipv4_src)");
+
+			ASSERT_EQ(fib_params->ipv4_src, expected_ipv4_src,
+			  "fib_lookup ipv4 src");
+		}
+		if (tests[i].expected_ipv6_src) {
+			__u32 expected_ipv6_src[4];
+
+			ret = inet_pton(AF_INET6, tests[i].expected_ipv6_src,
+					expected_ipv6_src);
+			ASSERT_EQ(ret, 1, "inet_pton(expected_ipv6_src)");
+
+			ret = memcmp(expected_ipv6_src, fib_params->ipv6_src,
+				     sizeof(fib_params->ipv6_src));
+			if (!ASSERT_EQ(ret, 0, "fib_lookup ipv6 src")) {
+				char src_ip6[64];
+
+				inet_ntop(AF_INET6, fib_params->ipv6_src, src_ip6,
+					  sizeof(src_ip6));
+				printf("ipv6 expected %s actual %s ",
+				       tests[i].expected_ipv6_src, src_ip6);
+			}
+		}
+
 		ret = memcmp(tests[i].dmac, fib_params->dmac, sizeof(tests[i].dmac));
 		if (!ASSERT_EQ(ret, 0, "dmac not match")) {
 			char expected[18], actual[18];
-- 
2.42.0