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Thu, 02 Apr 2026 20:38:42 -0700 (PDT) From: Qi Tang To: Alexei Starovoitov , Daniel Borkmann Cc: Kumar Kartikeya Dwivedi , Eduard Zingerman , Andrii Nakryiko , Martin KaFai Lau , John Fastabend , Song Liu , bpf@vger.kernel.org, Qi Tang Subject: [PATCH bpf v4 1/2] bpf: reject direct access to nullable PTR_TO_BUF pointers Date: Fri, 3 Apr 2026 11:38:27 +0800 Message-ID: <20260403033828.18529-2-tpluszz77@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260403033828.18529-1-tpluszz77@gmail.com> References: <20260403033828.18529-1-tpluszz77@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit check_mem_access() matches PTR_TO_BUF via base_type() which strips PTR_MAYBE_NULL, allowing direct dereference without a null check. Map iterator ctx->key and ctx->value are PTR_TO_BUF | PTR_MAYBE_NULL. On stop callbacks these are NULL, causing a kernel NULL dereference. Add a type_may_be_null() guard to the PTR_TO_BUF branch, matching the existing PTR_TO_BTF_ID pattern. Fixes: 20b2aff4bc15 ("bpf: Introduce MEM_RDONLY flag") Acked-by: Kumar Kartikeya Dwivedi Signed-off-by: Qi Tang --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 937c9adf1b3d..17850836943b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7905,7 +7905,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn } else if (reg->type == CONST_PTR_TO_MAP) { err = check_ptr_to_map_access(env, regs, regno, off, size, t, value_regno); - } else if (base_type(reg->type) == PTR_TO_BUF) { + } else if (base_type(reg->type) == PTR_TO_BUF && + !type_may_be_null(reg->type)) { bool rdonly_mem = type_is_rdonly_mem(reg->type); u32 *max_access; -- 2.43.0