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Mon, 27 Jul 2026 16:39:37 -0700 (PDT) Message-ID: <2fb1dd524daa3d74dcfc007af30f275ed431ce2a.camel@gmail.com> Subject: Re: [PATCH bpf-next v2 14/18] bpf: Check helper mem+size in ARG_PTR_TO_MEM case From: Eduard Zingerman To: Amery Hung , bpf@vger.kernel.org Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, memxor@gmail.com, kernel-team@meta.com Date: Mon, 27 Jul 2026 16:39:34 -0700 In-Reply-To: <20260724190813.1458271-15-ameryhung@gmail.com> References: <20260724190813.1458271-1-ameryhung@gmail.com> <20260724190813.1458271-15-ameryhung@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-07-24 at 12:08 -0700, Amery Hung wrote: ... > =C2=A0kernel/bpf/verifier.c | 16 +++++++--------- > =C2=A01 file changed, 7 insertions(+), 9 deletions(-) >=20 > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 144c2d8aa492..2326b12a1531 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -8505,9 +8505,6 @@ static int check_func_arg(struct bpf_verifier_env *= env, u32 arg, > =C2=A0 meta->subprogno =3D reg->subprogno; > =C2=A0 break; > =C2=A0 case ARG_PTR_TO_MEM: > - /* The access to this pointer is only checked when we hit the > - * next is_mem_size argument below. > - */ > =C2=A0 if (arg_type & MEM_FIXED_SIZE) { > =C2=A0 err =3D check_mem_reg(env, reg, argno_from_reg(regno), fn->arg_s= ize[arg], > =C2=A0 =C2=A0=C2=A0=C2=A0 arg_type & MEM_WRITE ? BPF_WRITE : BPF_READ= , meta); > @@ -8515,14 +8512,15 @@ static int check_func_arg(struct bpf_verifier_env= *env, u32 arg, > =C2=A0 return err; > =C2=A0 if (arg_type & MEM_ALIGNED) > =C2=A0 err =3D check_ptr_alignment(env, reg, 0, fn->arg_size[arg], tru= e); > + } else { > + struct bpf_reg_state *size_reg =3D reg_state(env, regno + 1); > + > + err =3D check_mem_size_reg(env, reg, size_reg, argno, > + argno_from_reg(regno + 1), > + arg_type & MEM_WRITE ? BPF_WRITE : BPF_READ, > + fn->arg_type[arg + 1] & SCALAR_MAYBE_ZERO, meta); > =C2=A0 } > =C2=A0 break; > - case ARG_MEM_SIZE: Nit: The ARG_MEM_SIZE would be ignored by this switch after the change, right? This is a correct thing to do, but I'd be a little bit more defensive. Let's modify this switch to: - explicitly skip ARG_MEM_SIZE - have default clause signalling a verifier error in case of unknown arg ty= pe. > - err =3D check_mem_size_reg(env, reg_state(env, regno - 1), reg, > - argno_from_reg(regno - 1), argno, > - fn->arg_type[arg - 1] & MEM_WRITE ? BPF_WRITE : BPF_READ, > - arg_type & SCALAR_MAYBE_ZERO, meta); > - break; > =C2=A0 case ARG_PTR_TO_DYNPTR: > =C2=A0 err =3D process_dynptr_func(env, reg, argno, insn_idx, arg_type, = &meta->ref_obj, > =C2=A0 =C2=A0 &meta->dynptr);