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([2620:10d:c090:500::2:bea8]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2e53d9b056fsm33363023eec.29.2026.04.22.15.46.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2026 15:46:38 -0700 (PDT) Message-ID: <9e477e253c202b10ed611213e4fc9a7017bfc51d.camel@gmail.com> Subject: Re: [PATCH bpf-next v3 3/9] bpf: Preserve reg->id of pointer objects after null-check From: Eduard Zingerman To: bot+bpf-ci@kernel.org, ameryhung@gmail.com, bpf@vger.kernel.org Cc: netdev@vger.kernel.org, alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, memxor@gmail.com, martin.lau@kernel.org, mykyta.yatsenko5@gmail.com, kernel-team@meta.com, ast@kernel.org, yonghong.song@linux.dev, clm@meta.com, ihor.solodrai@linux.dev Date: Wed, 22 Apr 2026 15:46:36 -0700 In-Reply-To: References: <20260421221016.2967924-4-ameryhung@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-04-21 at 22:52 +0000, bot+bpf-ci@kernel.org wrote: > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 93003a2a96b0..0313b7d5f6c9 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -15886,15 +15886,10 @@ static void mark_ptr_or_null_reg(struct bpf_f= unc_state *state, > >=20 > > =C2=A0 mark_ptr_not_null_reg(reg); > >=20 > > - if (!reg_may_point_to_spin_lock(reg)) { > > - /* For not-NULL ptr, reg->ref_obj_id will be reset > > - * in release_reference(). > > - * > > - * reg->id is still used by spin_lock ptr. Other > > - * than spin_lock ptr type, reg->id can be reset. > > - */ > > - reg->id =3D 0; > > - } > > + /* > > + * reg->id is preserved for object relationship tracking > > + * and spin_lock lock state tracking > > + */ >=20 > How does preserving reg->id interact with reg_is_init_pkt_pointer()? >=20 > In v2 review, Alexei Starovoitov raised this concern: "That pointer has > to have id =3D=3D 0". Eduard Zingerman responded that dropping the id =3D= =3D 0 > check should be fine, but this change was not made in v3. >=20 > The function reg_is_init_pkt_pointer() still checks reg->id =3D=3D 0: >=20 > =C2=A0=C2=A0=C2=A0=C2=A0return reg->type =3D=3D which && > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0reg->id= =3D=3D 0 && > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0reg->of= f =3D=3D 0 && >=20 > With this patch, if a PTR_TO_PACKET register goes through null-checking > in mark_ptr_or_null_reg(), it will now preserve its reg->id instead of > resetting it to 0. Would this cause reg_is_init_pkt_pointer() to > incorrectly return false for init packet pointers? >=20 > Reference: https://lore.kernel.org/bpf/CAADnVQLCKi_QL1FeybW+6MH6FAOAoRJyW= 06UvtX3my3yNSH5eQ@mail.gmail.com/ >=20 > > =C2=A0 } > > =C2=A0} Bot concern is bogus here, reg_is_init_pkt_pointer() is called only for PTR_TO_PACKET. mark_ptr_or_null_reg() checks for type_may_be_null(reg->type), meaning that for it to trigger one would need a register of type PTR_TO_PACKET | PTR_MAYBE_NULL. It appears there is no way to construct such type at the moment.