Question

我面临着bpf与最新net-next内核的奇怪行为。启用所有BPF内核选项（包括CONFIG_BPF_JIT_ALWAYS_ON）且未加载任何 bpf程序时，bpftool会报告以下内容：

# ./bpftool prog show
2: cgroup_skb  tag 7be49e3934a125ba
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 2,3
3: cgroup_skb  tag 2a142ef67aaad174
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 2,3
4: cgroup_skb  tag 7be49e3934a125ba
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 4,5
5: cgroup_skb  tag 2a142ef67aaad174
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 4,5
6: cgroup_skb  tag 7be49e3934a125ba
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 6,7
7: cgroup_skb  tag 2a142ef67aaad174
        loaded_at Feb 05/10:17  uid 0
        xlated 296B  jited 229B  memlock 4096B  map_ids 6,7
#
# ./bpftool map show
2: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
3: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
4: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
5: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
6: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
7: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
#

这是该程序包含的内容：

# ./bpftool prog dump xlated id 2
   0: (bf) r6 = r1
   1: (69) r7 = *(u16 *)(r6 +192)
   2: (b4) (u32) r8 = (u32) 0
   3: (55) if r7 != 0x8 goto pc+14
   4: (bf) r1 = r6
   5: (b4) (u32) r2 = (u32) 16
   6: (bf) r3 = r10
   7: (07) r3 += -4
   8: (b4) (u32) r4 = (u32) 4
   9: (85) call bpf_skb_load_bytes#6169312
  10: (18) r1 = map[id:2]
  12: (bf) r2 = r10
  13: (07) r2 += -8
  14: (62) *(u32 *)(r2 +0) = 32
  15: (85) call bpf_map_lookup_elem#73712
  16: (15) if r0 == 0x0 goto pc+1
  17: (44) (u32) r8 |= (u32) 2
  18: (55) if r7 != 0xdd86 goto pc+14
  19: (bf) r1 = r6
  20: (b4) (u32) r2 = (u32) 24
  21: (bf) r3 = r10
  22: (07) r3 += -16
  23: (b4) (u32) r4 = (u32) 16
  24: (85) call bpf_skb_load_bytes#6169312
  25: (18) r1 = map[id:3]
  27: (bf) r2 = r10
  28: (07) r2 += -20
  29: (62) *(u32 *)(r2 +0) = 128
  30: (85) call bpf_map_lookup_elem#73712
  31: (15) if r0 == 0x0 goto pc+1
  32: (44) (u32) r8 |= (u32) 2
  33: (b7) r0 = 1
  34: (55) if r8 != 0x2 goto pc+1
  35: (b7) r0 = 0
  36: (95) exit
#

有趣的是，我没有明确加载任何eBPF程序。我想知道现在内核中是否存在默认的eBPF blob，它会显示出来吗？

这在机器启动后立即发生。这个系统与另一个系统（运行相同的内核和选项，以及我没有看到多个cgroup_skb程序的这个问题）之间的唯一区别是/sys/fs/cgroup/unified cgroup2 FS的存在。我不知道这是否与我的问题有关，但我不知道如何禁用/sys/fs/cgroup/unified，不允许卸载。

Answer 1

正如Qeole所怀疑的那样，这是来自systemd，特别是systemd v235引入了IP访问控制eBPF功能，其中公开了两个配置选项，IPAddressDeny和IPAddressAllow。（我不知道是否可以在编译时禁用它。）

eBPF：默认的bpf程序/地图？

1 个答案: