On Fri, Dec 08, 2023 at 07:55:53PM +0100, Dmitrii Dolgov wrote:
SNIP
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index eb447b0a9423..e7393674ab94 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1414,6 +1414,7 @@ struct bpf_prog_aux {
> bool dev_bound; /* Program is bound to the netdev. */
> bool offload_requested; /* Program is bound and offloaded to the netdev. */
> bool attach_btf_trace; /* true if attaching to BTF-enabled raw tp */
> + bool attach_tracing_prog; /* true if tracing another tracing program */
> bool func_proto_unreliable;
> bool sleepable;
> bool tail_call_reachable;
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 5e43ddd1b83f..d5470a5c8c6d 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3039,6 +3039,7 @@ static void bpf_tracing_link_release(struct bpf_link *link)
>
> bpf_trampoline_put(tr_link->trampoline);
>
> + link->prog->aux->attach_tracing_prog = false;
I think it'd be better to have this as part of the 'if (tr_link->tgt_prog)'
path below, because it's set only for that case
> /* tgt_prog is NULL if target is a kernel function */
> if (tr_link->tgt_prog)
> bpf_prog_put(tr_link->tgt_prog);
> @@ -3243,6 +3244,12 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
> goto out_unlock;
> }
>
> + /* Bookkeeping for managing the prog attachment chain */
> + if (tgt_prog &&
> + prog->type == BPF_PROG_TYPE_TRACING &&
> + tgt_prog->type == BPF_PROG_TYPE_TRACING)
> + prog->aux->attach_tracing_prog = true;
wrong indentation in here, please check the if conditions around
thanks,
jirka
> +
> link->tgt_prog = tgt_prog;
> link->trampoline = tr;
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 8e7b6072e3f4..f8c15ce8fd05 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20077,6 +20077,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
> struct bpf_attach_target_info *tgt_info)
> {
> bool prog_extension = prog->type == BPF_PROG_TYPE_EXT;
> + bool prog_tracing = prog->type == BPF_PROG_TYPE_TRACING;
> const char prefix[] = "btf_trace_";
> int ret = 0, subprog = -1, i;
> const struct btf_type *t;
> @@ -20147,10 +20148,21 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
> bpf_log(log, "Can attach to only JITed progs\n");
> return -EINVAL;
> }
> - if (tgt_prog->type == prog->type) {
> - /* Cannot fentry/fexit another fentry/fexit program.
> - * Cannot attach program extension to another extension.
> - * It's ok to attach fentry/fexit to extension program.
> + if (prog_tracing) {
> + if (aux->attach_tracing_prog) {
> + /*
> + * Target program is an fentry/fexit which is already attached
> + * to another tracing program. More levels of nesting
> + * attachment are not allowed.
> + */
> + bpf_log(log, "Cannot nest tracing program attach more than once\n");
> + return -EINVAL;
> + }
> + } else if (tgt_prog->type == prog->type) {
> + /*
> + * To avoid potential call chain cycles, prevent attaching of a
> + * program extension to another extension. It's ok to attach
> + * fentry/fexit to extension program.
> */
> bpf_log(log, "Cannot recursively attach\n");
> return -EINVAL;
> @@ -20163,16 +20175,15 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
> * except fentry/fexit. The reason is the following.
> * The fentry/fexit programs are used for performance
> * analysis, stats and can be attached to any program
> - * type except themselves. When extension program is
> - * replacing XDP function it is necessary to allow
> - * performance analysis of all functions. Both original
> - * XDP program and its program extension. Hence
> - * attaching fentry/fexit to BPF_PROG_TYPE_EXT is
> - * allowed. If extending of fentry/fexit was allowed it
> - * would be possible to create long call chain
> - * fentry->extension->fentry->extension beyond
> - * reasonable stack size. Hence extending fentry is not
> - * allowed.
> + * type. When extension program is replacing XDP function
> + * it is necessary to allow performance analysis of all
> + * functions. Both original XDP program and its program
> + * extension. Hence attaching fentry/fexit to
> + * BPF_PROG_TYPE_EXT is allowed. If extending of
> + * fentry/fexit was allowed it would be possible to create
> + * long call chain fentry->extension->fentry->extension
> + * beyond reasonable stack size. Hence extending fentry
> + * is not allowed.
> */
> bpf_log(log, "Cannot extend fentry/fexit\n");
> return -EINVAL;
> --
> 2.41.0
>
