On Thu, Dec 12, 2019 at 3:34 PM Andrey Ignatov <rdna@xxxxxx> wrote:
>
> Test replacement of a cgroup-bpf program attached with BPF_F_ALLOW_MULTI
> and possible failure modes: invalid combination of flags, invalid
> replace_bpf_fd, replacing a non-attachd to specified cgroup program.
>
> Example of program replacing:
>
> # gdb -q ./test_cgroup_attach
> Reading symbols from /data/users/rdna/bin/test_cgroup_attach...done.
> ...
> Breakpoint 1, test_multiprog () at test_cgroup_attach.c:443
> 443 test_cgroup_attach.c: No such file or directory.
> (gdb)
> [2]+ Stopped gdb -q ./test_cgroup_attach
> # bpftool c s /mnt/cgroup2/cgroup-test-work-dir/cg1
> ID AttachType AttachFlags Name
> 35 egress multi
> 36 egress multi
> # fg gdb -q ./test_cgroup_attach
> c
> Continuing.
> Detaching after fork from child process 361.
>
> Breakpoint 2, test_multiprog () at test_cgroup_attach.c:454
> 454 in test_cgroup_attach.c
> (gdb)
> [2]+ Stopped gdb -q ./test_cgroup_attach
> # bpftool c s /mnt/cgroup2/cgroup-test-work-dir/cg1
> ID AttachType AttachFlags Name
> 41 egress multi
> 36 egress multi
>
> Signed-off-by: Andrey Ignatov <rdna@xxxxxx>
> ---
> .../selftests/bpf/test_cgroup_attach.c | 62 +++++++++++++++++--
> 1 file changed, 57 insertions(+), 5 deletions(-)
>
I second Alexei's sentiment. Having this as part of test_progs would
certainly be better in terms of ensuring this doesn't accidentally
breaks.
[...]
>
> + /* invalid input */
> +
> + DECLARE_LIBBPF_OPTS(bpf_prog_attach_opts, attach_opts,
> + .target_fd = cg1,
> + .prog_fd = allow_prog[6],
> + .replace_prog_fd = allow_prog[0],
> + .type = BPF_CGROUP_INET_EGRESS,
> + .flags = BPF_F_ALLOW_MULTI | BPF_F_REPLACE,
> + );
This might cause compiler warnings (depending on compiler settings, of
course). DECLARE_LIBBPF_OPTS does declare variable, so this is a
situation of mixing code and variable declarations, which under C89
(or whatever it's named, the older standard that kernel is trying to
stick to for the most part) is not allowed.
> +
> + attach_opts.flags = BPF_F_ALLOW_OVERRIDE | BPF_F_REPLACE;
> + if (!bpf_prog_attach_xattr(&attach_opts)) {
> + log_err("Unexpected success with OVERRIDE | REPLACE");
> + goto err;
> + }
> + assert(errno == EINVAL);
> +
