On Wed, Aug 21, 2024 at 2:30 AM Tze-nan Wu <Tze-nan.Wu@xxxxxxxxxxxx> wrote:
>
> The return value from `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` can change
> between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> `BPF_CGROUP_RUN_PROG_GETSOCKOPT`.
>
> If `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` changes from "false" to
> "true" between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> `BPF_CGROUP_RUN_PROG_GETSOCKOPT`, `BPF_CGROUP_RUN_PROG_GETSOCKOPT` will
> receive an -EFAULT from `__cgroup_bpf_run_filter_getsockopt(max_optlen=0)`
> due to `get_user()` was not reached in `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`.
>
> Scenario shown as below:
>
> `process A` `process B`
> ----------- ------------
> BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN
> enable CGROUP_GETSOCKOPT
> BPF_CGROUP_RUN_PROG_GETSOCKOPT (-EFAULT)
>
> To prevent this, invoke `cgroup_bpf_enabled()` only once and cache the
> result in a newly added local variable `enabled`.
> Both `BPF_CGROUP_*` macros in `do_sock_getsockopt` will then check their
> condition using the same `enabled` variable as the condition variable,
> instead of using the return values from `cgroup_bpf_enabled` called by
> themselves as the condition variable(which could yield different results).
> This ensures that either both `BPF_CGROUP_*` macros pass the condition
> or neither does.
>
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Co-developed-by: Yanghui Li <yanghui.li@xxxxxxxxxxxx>
> Signed-off-by: Yanghui Li <yanghui.li@xxxxxxxxxxxx>
> Co-developed-by: Cheng-Jui Wang <cheng-jui.wang@xxxxxxxxxxxx>
> Signed-off-by: Cheng-Jui Wang <cheng-jui.wang@xxxxxxxxxxxx>
> Signed-off-by: Tze-nan Wu <Tze-nan.Wu@xxxxxxxxxxxx>
> ---
>
> Chagnes from v1 to v2: https://lore.kernel.org/all/20240819082513.27176-1-Tze-nan.Wu@xxxxxxxxxxxx/
> Instead of using cgroup_lock in the fastpath, invoke cgroup_bpf_enabled
> only once and cache the value in the newly added variable `enabled`.
> `BPF_CGROUP_*` macros in do_sock_getsockopt can then both check their
> condition with the new variable `enable`, ensuring that either they both
> passing the condition or both do not.
>
> Chagnes from v2 to v3: https://lore.kernel.org/all/20240819155627.1367-1-Tze-nan.Wu@xxxxxxxxxxxx/
> Hide cgroup_bpf_enabled in the macro, and some modifications to adapt
> the coding style.
>
> Chagnes from v3 to v4: https://lore.kernel.org/all/20240820092942.16654-1-Tze-nan.Wu@xxxxxxxxxxxx/
> Add bpf tag to subject, and Fixes tag in body.
>
> ---
> include/linux/bpf-cgroup.h | 15 ++++++++-------
> net/socket.c | 5 +++--
> 2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> index fb3c3e7181e6..5afa2ac76aae 100644
> --- a/include/linux/bpf-cgroup.h
> +++ b/include/linux/bpf-cgroup.h
> @@ -390,20 +390,20 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
> __ret; \
> })
>
> -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) \
> +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled) \
> ({ \
> int __ret = 0; \
> - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT)) \
> + enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT); \
> + if (enabled)
I suspect the compiler generates slow code after such a patch.
pw-bot: cr
What is the problem with double cgroup_bpf_enabled() check?
yes it might return two different values, so?
