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Thu, 04 Jun 2026 11:35:48 -0700 (PDT) From: Suchit Karunakaran X-Google-Original-From: Suchit Karunakaran Date: Fri, 5 Jun 2026 00:05:40 +0530 To: Nuiqi Gui Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, dxu@dxuuu.xyz, stable@vger.kernel.org, John Fastabend , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf 1/2] bpf: Keep dynamic inner array lookups nullable Message-ID: References: <20260604151153.2488051-1-gnq25@mails.tsinghua.edu.cn> <20260604151153.2488051-2-gnq25@mails.tsinghua.edu.cn> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260604151153.2488051-2-gnq25@mails.tsinghua.edu.cn> On Thu, Jun 04, 2026 at 11:11:52PM +0800, Nuiqi Gui wrote: > An ARRAY_OF_MAPS can use an array created with BPF_F_INNER_MAP as its > inner map template. A concrete inner array with a different max_entries > value can then replace the template. > > After a successful outer map lookup, the verifier represents the > resulting map pointer using the inner map template. Const-key lookup > nullness elision consequently uses the template max_entries even though > the runtime helper uses the concrete inner map max_entries. > > Do not elide lookup result nullness for maps marked with BPF_F_INNER_MAP, > because the template max_entries does not prove that the key is in bounds > for the concrete runtime map. > > Fixes: d2102f2f5d75 ("bpf: verifier: Support eliding map lookup nullness") > Cc: stable@vger.kernel.org > Signed-off-by: Nuiqi Gui > --- > kernel/bpf/verifier.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 7fb88e1cd7c4d..bffe12d0bb289 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -8471,7 +8471,7 @@ static int get_constant_map_key(struct bpf_verifier_env *env, > return 0; > } > > -static bool can_elide_value_nullness(enum bpf_map_type type); > +static bool can_elide_value_nullness(const struct bpf_map *map); > > static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > struct bpf_call_arg_meta *meta, > @@ -8621,7 +8621,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > err = check_helper_mem_access(env, regno, key_size, BPF_READ, false, NULL); > if (err) > return err; > - if (can_elide_value_nullness(meta->map.ptr->map_type)) { > + if (can_elide_value_nullness(meta->map.ptr)) { > err = get_constant_map_key(env, reg, key_size, &meta->const_map_key); > if (err < 0) { > meta->const_map_key = -1; > @@ -10225,9 +10225,12 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno > * lookup return value nullness check. This is possible if the key > * is statically known. > */ > -static bool can_elide_value_nullness(enum bpf_map_type type) > +static bool can_elide_value_nullness(const struct bpf_map *map) > { > - switch (type) { > + if (map->map_flags & BPF_F_INNER_MAP) > + return false; One small nit: the can_elide_value_nullness() function comment appears to be out of sync with the updated parameter. Resending because somehow my mutt config got messed up with my other email address.