bpf: fix null pointer deref in bpf_prog_test_run_xdp

syzkaller was able to generate the following XDP program ...

  (18) r0 = 0x0
  (61) r5 = *(u32 *)(r1 +12)
  (04) (u32) r0 += (u32) 0
  (95) exit

... and trigger a NULL pointer dereference in ___bpf_prog_run()
via bpf_prog_test_run_xdp() where this was attempted to run.

Reason is that recent xdp_rxq_info addition to XDP programs
updated all drivers, but not bpf_prog_test_run_xdp(), where
xdp_buff is set up. Thus when context rewriter does the deref
on the netdev it's NULL at runtime. Fix it by using xdp_rxq
from loopback dev. __netif_get_rx_queue() helper can also be
reused in various other locations later on.

Fixes: 02dd3291b2f0 ("bpf: finally expose xdp_rxq_info to XDP bpf-programs")
Reported-by: syzbot+1eb094057b338eb1fc00@syzkaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4c77f39..5eef6c8 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3228,6 +3228,12 @@ static inline int netif_set_real_num_rx_queues(struct net_device *dev,
 }
 #endif
 
+static inline struct netdev_rx_queue *
+__netif_get_rx_queue(struct net_device *dev, unsigned int rxq)
+{
+       return dev->_rx + rxq;
+}
+
 #ifdef CONFIG_SYSFS
 static inline unsigned int get_netdev_rx_queue_index(
                struct netdev_rx_queue *queue)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index a86e668..2ced486 100644 (file)
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -151,6 +151,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 {
        u32 size = kattr->test.data_size_in;
        u32 repeat = kattr->test.repeat;
+       struct netdev_rx_queue *rxqueue;
        struct xdp_buff xdp = {};
        u32 retval, duration;
        void *data;
@@ -165,6 +166,9 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
        xdp.data_meta = xdp.data;
        xdp.data_end = xdp.data + size;
 
+       rxqueue = __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 0);
+       xdp.rxq = &rxqueue->xdp_rxq;
+
        retval = bpf_test_run(prog, &xdp, repeat, &duration);
        if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN)
                size = xdp.data_end - xdp.data;

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 697bd83..c0f16e9 100644 (file)
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -7780,6 +7780,20 @@ static struct bpf_test tests[] = {
                .result = REJECT,
        },
        {
+               "XDP, using ifindex from netdev",
+               .insns = {
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
+                                   offsetof(struct xdp_md, ingress_ifindex)),
+                       BPF_JMP_IMM(BPF_JLT, BPF_REG_2, 1, 1),
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_EXIT_INSN(),
+               },
+               .result = ACCEPT,
+               .prog_type = BPF_PROG_TYPE_XDP,
+               .retval = 1,
+       },
+       {
                "meta access, test1",
                .insns = {
                        BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,