• Yonghong Song's avatar
    bpf/cgroup: fix a verification error for a CGROUP_DEVICE type prog · 06ef0ccb
    Yonghong Song authored
    The tools/testing/selftests/bpf test program
    test_dev_cgroup fails with the following error
    when compiled with llvm 6.0. (I did not try
    with earlier versions.)
    
      libbpf: load bpf program failed: Permission denied
      libbpf: -- BEGIN DUMP LOG ---
      libbpf:
      0: (61) r2 = *(u32 *)(r1 +4)
      1: (b7) r0 = 0
      2: (55) if r2 != 0x1 goto pc+8
       R0=inv0 R1=ctx(id=0,off=0,imm=0) R2=inv1 R10=fp0
      3: (69) r2 = *(u16 *)(r1 +0)
      invalid bpf_context access off=0 size=2
      ...
    
    The culprit is the following statement in dev_cgroup.c:
      short type = ctx->access_type & 0xFFFF;
    This code is typical as the ctx->access_type is assigned
    as below in kernel/bpf/cgroup.c:
      struct bpf_cgroup_dev_ctx ctx = {
            .access_type = (access << 16) | dev_type,
            .major = major,
            .minor = minor,
      };
    
    The compiler converts it to u16 access while
    the verifier cgroup_dev_is_valid_access rejects
    any non u32 access.
    
    This patch permits the field access_type to be accessible
    with type u16 and u8 as well.
    Signed-off-by: default avatarYonghong Song <yhs@fb.com>
    Tested-by: default avatarRoman Gushchin <guro@fb.com>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    06ef0ccb
cgroup.c 15.8 KB