On Thu, Nov 2, 2023 at 10:55 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> Andrii Nakryiko <andrii@xxxxxxxxxx> writes:
>
> > Let's fix it for real this time. It shouldn't just detect ERR_PTR()
> > return from bpf_xdp_pointer(), but also turn that into NULL to follow
> > bpf_dynptr_slice() contract.
> >
> > Fixes: 5426700e6841 ("bpf: fix bpf_dynptr_slice() to stop return an ERR_PTR.")
> > Fixes: 66e3a13e7c2c ("bpf: Add bpf_dynptr_slice and bpf_dynptr_slice_rdwr")
> > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > ---
> > kernel/bpf/helpers.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index 56b0c1f678ee..04049097176c 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -2309,7 +2309,7 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset
> > {
> > void *xdp_ptr = bpf_xdp_pointer(ptr->data, ptr->offset + offset, len);
> > if (!IS_ERR_OR_NULL(xdp_ptr))
> > - return xdp_ptr;
> > + return NULL;
>
> Erm, the check in the if is inverted - so isn't this 'return xdp_ptr'
> covering the case where bpf_xdp_pointer() *does* in fact return a valid
> pointer?
>
Ah, you are right, I missed the ! part... Ok, then I don't think we
have an issue, great. Thanks for double checking!
Perhaps we should add a simple comment "/* we got a valid direct
pointer, return it */", as this looks like an error-handling case.
> -Toke
