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([2620:10d:c090:500::3:1322]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3074df191d0sm31809976eec.21.2026.06.09.10.01.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2026 10:01:09 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next 1/2] bpf: Reject scalar addition from untrusted memory From: Eduard Zingerman To: Nuoqi Gui , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Kumar Kartikeya Dwivedi , John Fastabend , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Shuah Khan , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Tue, 09 Jun 2026 10:01:07 -0700 In-Reply-To: <20260609-f01-03-scalar-add-bpf-next-v1-1-e6212e274155@mails.tsinghua.edu.cn> References: <20260609-f01-03-scalar-add-bpf-next-v1-0-e6212e274155@mails.tsinghua.edu.cn> <20260609-f01-03-scalar-add-bpf-next-v1-1-e6212e274155@mails.tsinghua.edu.cn> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-06-09 at 22:55 +0800, Nuoqi Gui wrote: > scalar +=3D rdonly_untrusted_mem reaches adjust_ptr_min_max_vals() with t= he > pointer as the source register. The untrusted PTR_TO_MEM case returns the= re > without updating the scalar destination, leaving stale verifier state. >=20 > Reject that addition before the early return. Pointer +=3D scalar remains > handled by the existing untrusted-memory rule. >=20 > Fixes: f2362a57aeff ("bpf: allow void* cast using bpf_rdonly_cast()") > Signed-off-by: Nuoqi Gui > --- > kernel/bpf/verifier.c | 8 ++++++++ > 1 file changed, 8 insertions(+) >=20 > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index c8d980fdd709..c6b350f9585a 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -14823,6 +14823,14 @@ static int adjust_reg_min_max_vals(struct bpf_ve= rifier_env *env, > * This is legal, but we have to reverse our > * src/dest handling in computing the range > */ > + if (opcode =3D=3D BPF_ADD && > + base_type(src_reg->type) =3D=3D PTR_TO_MEM && > + (src_reg->type & PTR_UNTRUSTED)) { > + verbose(env, "R%d tried to add from %s to scalar\n", > + insn->dst_reg, > + reg_type_str(env, src_reg->type)); > + return -EACCES; > + } > err =3D mark_chain_precision(env, insn->dst_reg); > if (err) > return err; Should the fix be like this: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7d27ba396d32..9c85dd680a46 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13593,8 +13593,10 @@ static int adjust_ptr_min_max_vals(struct bpf_ve= rifier_env *env, * Accesses to untrusted PTR_TO_MEM are done through probe * instructions, hence no need to track offsets. */ - if (base_type(ptr_reg->type) =3D=3D PTR_TO_MEM && (ptr_reg->type = & PTR_UNTRUSTED)) + if (base_type(ptr_reg->type) =3D=3D PTR_TO_MEM && (ptr_reg->type = & PTR_UNTRUSTED)) { + *dst_reg =3D *ptr_reg; return 0; + } =20 switch (base_type(ptr_reg->type)) { case PTR_TO_CTX: Instead?