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Sat, 05 Sep 2026 20:46:33 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf v1 1/2] bpf: Reject non-scalar bpf_loop iteration counts From: Eduard Zingerman To: Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: syzbot+7b47f87674e9a1569110@syzkaller.appspotmail.com, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Emil Tsalapatis , kkd@meta.com, kernel-team@meta.com Date: Sat, 05 Sep 2026 20:46:30 -0700 In-Reply-To: <20260905014735.1452988-2-memxor@gmail.com> References: <20260905014735.1452988-1-memxor@gmail.com> <20260905014735.1452988-2-memxor@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10+b1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2026-09-05 at 03:47 +0200, Kumar Kartikeya Dwivedi wrote: > bpf_loop() declares its nr_loops argument as ARG_ANYTHING. Privileged > programs may pass pointer values to such arguments, so check_func_arg() > lets a pointer-valued R1 reach the helper-specific checks. >=20 > Since commit bb124da69c47 ("bpf: keep track of max number of bpf_loop > callback iterations"), the verifier marks R1 precise and reads its upper > bound to limit callback simulation. Precision backtracking only accepts > scalar registers, so passing a pointer instead triggers the "backtracking > misuse" verifier warning. Kernels with panic_on_warn enabled subsequently > panic. >=20 > Introduce ARG_SCALAR for helper arguments that only accept scalar values > and use it for bpf_loop() nr_loops. Generic helper argument validation th= en > rejects pointers before loop inlining and precision processing. >=20 > Fixes: bb124da69c47 ("bpf: keep track of max number of bpf_loop callback = iterations") > Reported-by: syzbot+7b47f87674e9a1569110@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/bpf/6a9ad24c.b5d4176b.238c3e.0001.GAE@goo= gle.com/ > Signed-off-by: Kumar Kartikeya Dwivedi > --- Acked-by: Eduard Zingerman Looks like there are no other instances of this bug.