Re: [PATCH bpf-next v2 5/9] selftests: bpf: Update failure message for rbtree_fail

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-12-31 at 19:44 +0000, Puranjay Mohan wrote:
> On Wed, Dec 31, 2025 at 7:27 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
> > 
> > On Wed, 2025-12-31 at 09:08 -0800, Puranjay Mohan wrote:
> > > The rbtree_api_use_unchecked_remove_retval() selftest passes a pointer
> > > received from bpf_rbtree_remove() to bpf_rbtree_add() without checking
> > > for NULL, this was earlier caught by __check_ptr_off_reg() in the
> > > verifier. Now the verifier assumes every kfunc only takes trusted pointer
> > > arguments, so it catches this NULL pointer earlier in the path and
> > > provides a more accurate failure message.
> > > 
> > > Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
> > > ---
> > 
> > Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> > 
> > >  tools/testing/selftests/bpf/progs/rbtree_fail.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/tools/testing/selftests/bpf/progs/rbtree_fail.c b/tools/testing/selftests/bpf/progs/rbtree_fail.c
> > > index 4acb6af2dfe3..70b7baf9304b 100644
> > > --- a/tools/testing/selftests/bpf/progs/rbtree_fail.c
> > > +++ b/tools/testing/selftests/bpf/progs/rbtree_fail.c
> > > @@ -153,7 +153,7 @@ long rbtree_api_add_to_multiple_trees(void *ctx)
> > >  }
> > > 
> > >  SEC("?tc")
> > > -__failure __msg("dereference of modified ptr_or_null_ ptr R2 off=16 disallowed")
> > > +__failure __msg("Possibly NULL pointer passed to trusted arg1")
> > >  long rbtree_api_use_unchecked_remove_retval(void *ctx)
> > >  {
> > >       struct bpf_rb_node *res;
> > 
> > Do you happen to know how did it infer off=16 for R2?
> > From the test I would infer that the off is zero.
> 
> I thought about that too,
> 
> struct node_data {
>     long key;
>     long data;
>     struct bpf_rb_node node;
> };
> 
> the node is at an offset of 16 and bpf_rbtree_remove() returns the
> pointer to this node.

Oh, makes sense, thank you.