Re: [PATCHv2 bpf-next 09/23] bpf: Add support for tracing multi link

[Jiri Olsa]

On Wed, Mar 04, 2026 at 11:02:30PM +0000, bot+bpf...@kernel.org wrote:
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> 
> [ ... ]
> 
> > +int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr 
> > *attr)
> > +{
> > +   struct bpf_tracing_multi_link *link = NULL;
> > +   struct bpf_link_primer link_primer;
> > +   u32 cnt, *ids = NULL;
> > +   u32 __user *uids;
> > +   int err;
> > +
> > +   uids = u64_to_user_ptr(attr->link_create.tracing_multi.ids);
> > +   cnt = attr->link_create.tracing_multi.cnt;
> > +
> > +   if (!cnt || !uids)
> > +           return -EINVAL;
> 
> Should attr->link_create.flags be validated here as well?
> 
> Both bpf_kprobe_multi_link_attach() and bpf_uprobe_multi_link_attach()
> reject non-zero flags:
> 
> kernel/trace/bpf_trace.c:bpf_kprobe_multi_link_attach() {
>     ...
>     if (attr->link_create.flags)
>         return -EINVAL;
>     ...
> }

argh right, that's missing, will fix, thnx

> 
> Without this check, userspace passing flags != 0 will be silently
> accepted, which would prevent using the flags field for future
> extensions since old kernels could not be distinguished from new
> ones.
> 
> > +   if (cnt > MAX_TRACING_MULTI_CNT)
> > +           return -E2BIG;
> 
> [ ... ]
> 
> > +#else
> > +
> > +int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr 
> > *attr)
> > +{
> > +   return -EOPNOTSUPP;
> > +}
> > +
> > +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS) && 
> > CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS */
> 
> Minor: there is a stray ')' after CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> in this comment.

yep, will remove, thnx

jirka