On Thu, Nov 09, 2023 at 09:57:03PM -0800, Andrii Nakryiko wrote:
SNIP
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 52c1ec3a0467..1ea54f3b3f73 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -3046,6 +3046,7 @@ struct bpf_uprobe_multi_link {
> > u32 cnt;
> > struct bpf_uprobe *uprobes;
> > struct task_struct *task;
> > + u32 flags;
> > };
> >
> > struct bpf_uprobe_multi_run_ctx {
> > @@ -3085,9 +3086,76 @@ static void bpf_uprobe_multi_link_dealloc(struct bpf_link *link)
> > kfree(umulti_link);
> > }
> >
> > +static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
> > + struct bpf_link_info *info)
> > +{
> > + u64 __user *uref_ctr_offsets = u64_to_user_ptr(info->uprobe_multi.ref_ctr_offsets);
> > + u64 __user *ucookies = u64_to_user_ptr(info->uprobe_multi.cookies);
> > + u64 __user *uoffsets = u64_to_user_ptr(info->uprobe_multi.offsets);
> > + u64 __user *upath = u64_to_user_ptr(info->uprobe_multi.path);
> > + u32 upath_size = info->uprobe_multi.path_size;
> > + struct bpf_uprobe_multi_link *umulti_link;
> > + u32 ucount = info->uprobe_multi.count;
> > + int err = 0, i;
> > + long left;
> > +
> > + if (!upath ^ !upath_size)
> > + return -EINVAL;
> > +
> > + if (!uoffsets ^ !ucount)
>
> uoffsets is not the only one that requires ucount, right?
yep, cookies as well
>
> > + return -EINVAL;
> > +
> > + umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> > + info->uprobe_multi.count = umulti_link->cnt;
> > + info->uprobe_multi.flags = umulti_link->flags;
> > + info->uprobe_multi.pid = umulti_link->task ?
> > + task_pid_nr_ns(umulti_link->task, task_active_pid_ns(current)) : 0;
> > +
> > + if (upath) {
> > + char *p, *buf;
> > +
> > + upath_size = min_t(u32, upath_size, PATH_MAX);
> > +
> > + buf = kmalloc(upath_size, GFP_KERNEL);
> > + if (!buf)
> > + return -ENOMEM;
> > + p = d_path(&umulti_link->path, buf, upath_size);
> > + if (IS_ERR(p)) {
> > + kfree(buf);
> > + return -ENOSPC;
> > + }
> > + left = copy_to_user(upath, p, buf + upath_size - p);
> > + kfree(buf);
> > + if (left)
> > + return -EFAULT;
>
> hmm.. I expected the actual path_size to be reported back to the
> user?.. Is there a problem with doing that?
we return back the string, if the string fits in provided buffer it's
terminated with 0 and user space can do strlen on it if needed
>
> > + }
> > +
> > + if (!uoffsets)
> > + return 0;
>
> why guard by uoffsets? what if users only wanted cookies? I think each
> array should do its own checking and be independent, no?
I did not think of the use case to get just the cookies (at least not the
one in bpftool), I saw it as optional to offsets, which is mandatory..
but that should be an easy change I think
jirka
>
> > +
> > + if (ucount < umulti_link->cnt)
> > + err = -ENOSPC;
> > + else
> > + ucount = umulti_link->cnt;
> > +
> > + for (i = 0; i < ucount; i++) {
> > + if (put_user(umulti_link->uprobes[i].offset, uoffsets + i))
> > + return -EFAULT;
> > + if (uref_ctr_offsets &&
> > + put_user(umulti_link->uprobes[i].ref_ctr_offset, uref_ctr_offsets + i))
> > + return -EFAULT;
> > + if (ucookies &&
> > + put_user(umulti_link->uprobes[i].cookie, ucookies + i))
> > + return -EFAULT;
> > + }
> > +
> > + return err;
> > +}
> > +
> > static const struct bpf_link_ops bpf_uprobe_multi_link_lops = {
> > .release = bpf_uprobe_multi_link_release,
> > .dealloc = bpf_uprobe_multi_link_dealloc,
> > + .fill_link_info = bpf_uprobe_multi_link_fill_link_info,
> > };
> >
> > static int uprobe_prog_run(struct bpf_uprobe *uprobe,
> > @@ -3276,6 +3344,7 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> > link->uprobes = uprobes;
> > link->path = path;
> > link->task = task;
> > + link->flags = flags;
> >
> > bpf_link_init(&link->link, BPF_LINK_TYPE_UPROBE_MULTI,
> > &bpf_uprobe_multi_link_lops, prog);
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index 0f6cdf52b1da..05b355da4508 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -6556,6 +6556,16 @@ struct bpf_link_info {
> > __u32 flags;
> > __u64 missed;
> > } kprobe_multi;
> > + struct {
> > + __aligned_u64 path;
> > + __aligned_u64 offsets;
> > + __aligned_u64 ref_ctr_offsets;
> > + __aligned_u64 cookies;
> > + __u32 path_size;
> > + __u32 count; /* in/out: uprobe_multi offsets/ref_ctr_offsets/cookies count */
> > + __u32 flags;
> > + __u32 pid;
> > + } uprobe_multi;
> > struct {
> > __u32 type; /* enum bpf_perf_event_type */
> > __u32 :32;
> > --
> > 2.41.0
> >
