1. 21 Jan, 2022 34 commits
  2. 20 Jan, 2022 5 commits
  3. 19 Jan, 2022 1 commit
    • Alexei Starovoitov's avatar
      Merge branch 'bpf: allow cgroup progs to export custom retval to userspace' · 4e950747
      Alexei Starovoitov authored
      YiFei Zhu says:
      
      ====================
      
      Right now, most cgroup hooks are best used for permission checks. They
      can only reject a syscall with -EPERM, so a cause of a rejection, if
      the rejected by eBPF cgroup hooks, is ambiguous to userspace.
      Additionally, if the syscalls are implemented in eBPF, all permission
      checks and the implementation has to happen within the same filter,
      as programs executed later in the series of progs are unaware of the
      return values return by the previous progs.
      
      This patch series adds two helpers, bpf_get_retval and bpf_set_retval,
      that allows hooks to get/set the return value of syscall to userspace.
      This also allows later progs to retrieve retval set by previous progs.
      
      For legacy programs that rejects a syscall without setting the retval,
      for backwards compatibility, if a prog rejects without itself or a
      prior prog setting retval to an -err, the retval is set by the kernel
      to -EPERM.
      
      For getsockopt hooks that has ctx->retval, this variable mirrors that
      that accessed by the helpers.
      
      Additionally, the following user-visible behavior for getsockopt
      hooks has changed:
        - If a prior filter rejected the syscall, it will be visible
          in ctx->retval.
        - Attempting to change the retval arbitrarily is now allowed and
          will not cause an -EFAULT.
        - If kernel rejects a getsockopt syscall before running the hooks,
          the error will be visible in ctx->retval. Returning 0 from the
          prog will not overwrite the error to -EPERM unless there is an
          explicit call of bpf_set_retval(-EPERM)
      
      Tests have been added in this series to test the behavior of the helper
      with cgroup setsockopt getsockopt hooks.
      
      Patch 1 changes the API of macros to prepare for the next patch and
        should be a no-op.
      Patch 2 moves ctx->retval to a struct pointed to by current
        task_struct.
      Patch 3 implements the helpers.
      Patch 4 tests the behaviors of the helpers.
      Patch 5 updates a test after the test broke due to the visible changes.
      
      v1 -> v2:
        - errno -> retval
        - split one helper to get & set helpers
        - allow retval to be set arbitrarily in the general case
        - made the helper retval and context retval mirror each other
      ====================
      Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      4e950747