When using BPF_PROG_ATTACH to attach a program to a cgroup in
BPF_F_ALLOW_MULTI mode, it is not possible to replace a program
with itself. This is because the check for duplicate programs
doesn't take the replacement program into account.
Replacing a program with itself might seem weird, but it has
some uses: first, it allows resetting the associated cgroup storage.
Second, it makes the API consistent with the non-ALLOW_MULTI usage,
where it is possible to replace a program with itself. Third, it
aligns BPF_PROG_ATTACH with bpf_link, where replacing itself is
also supported.
Sice this code has been refactored a few times this change will
only apply to v5.7 and later. Adjustments could be made to
commit 1020c1f24a ("bpf: Simplify __cgroup_bpf_attach") and
commit d7bf2c10af ("bpf: allocate cgroup storage entries on attaching bpf programs")
as well as commit 324bda9e6c ("bpf: multi program support for cgroup+bpf")
Fixes: af6eea5743 ("bpf: Implement bpf_link-based cgroup BPF program attachment")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200608162202.94002-1-lmb@cloudflare.com
The cgroup selftests did not declare the bpf_log_buf variable as static, leading
to a linker error with GCC 10 (which defaults to -fno-common). Fix this by
adding the missing static declarations.
Fixes: 257c88559f ("selftests/bpf: Convert test_cgroup_attach to prog_tests")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrey Ignatov <rdna@fb.com>
Link: https://lore.kernel.org/bpf/20200302145348.559177-1-toke@redhat.com
Test replacing 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 --args ./test_progs --name=cgroup_attach_multi
...
Breakpoint 1, test_cgroup_attach_multi () at cgroup_attach_multi.c:227
(gdb)
[1]+ Stopped gdb -q --args ./test_progs --name=cgroup_attach_multi
# bpftool c s /mnt/cgroup2/cgroup-test-work-dir/cg1
ID AttachType AttachFlags Name
2133 egress multi
2134 egress multi
# fg
gdb -q --args ./test_progs --name=cgroup_attach_multi
(gdb) c
Continuing.
Breakpoint 2, test_cgroup_attach_multi () at cgroup_attach_multi.c:233
(gdb)
[1]+ Stopped gdb -q --args ./test_progs --name=cgroup_attach_multi
# bpftool c s /mnt/cgroup2/cgroup-test-work-dir/cg1
ID AttachType AttachFlags Name
2139 egress multi
2134 egress multi
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/7b9b83e8d5fb82e15b034341bd40b6fb2431eeba.1576741281.git.rdna@fb.com
Convert test_cgroup_attach to prog_tests.
This change does a lot of things but in many cases it's pretty expensive
to separate them, so they go in one commit. Nevertheless the logic is
ketp as is and changes made are just moving things around, simplifying
them (w/o changing the meaning of the tests) and making prog_tests
compatible:
* split the 3 tests in the file into 3 separate files in prog_tests/;
* rename the test functions to test_<file_base_name>;
* remove unused includes, constants, variables and functions from every
test;
* replace `if`-s with or `if (CHECK())` where additional context should
be logged and with `if (CHECK_FAIL())` where line number is enough;
* switch from `log_err()` to logging via `CHECK()`;
* replace `assert`-s with `CHECK_FAIL()` to avoid crashing the whole
test_progs if one assertion fails;
* replace cgroup_helpers with test__join_cgroup() in
cgroup_attach_override only, other tests need more fine-grained
control for cgroup creation/deletion so cgroup_helpers are still used
there;
* simplify cgroup_attach_autodetach by switching to easiest possible
program since this test doesn't really need such a complicated program
as cgroup_attach_multi does;
* remove test_cgroup_attach.c itself.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/0ff19cc64d2dc5cf404349f07131119480e10e32.1576741281.git.rdna@fb.com
