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Wed, 22 Jul 2026 22:08:14 -0700 (PDT) Received: from localhost ([2a03:2880:ff:45::]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-38ecaac56a7sm294074a91.11.2026.07.22.22.08.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 22:08:14 -0700 (PDT) From: Amery Hung To: bpf@vger.kernel.org Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, memxor@gmail.com, ameryhung@gmail.com, kernel-team@meta.com Subject: [PATCH bpf-next v1 05/18] bpf: Check helper and kfunc mem+size arguments identically Date: Wed, 22 Jul 2026 22:07:53 -0700 Message-ID: <20260723050806.1158442-6-ameryhung@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260723050806.1158442-1-ameryhung@gmail.com> References: <20260723050806.1158442-1-ameryhung@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 Helper ARG_CONST_SIZE and kfunc KF_ARG_PTR_TO_MEM_SIZE memory arguments already share check_mem_size_reg(), but only the kfunc wrapper check_kfunc_mem_size_reg() ran mark_ptr_not_null_reg() on a possibly-NULL pointer before the access check. That call does more than clearing PTR_MAYBE_NULL: it converts special map-value-or-null registers to their real non-NULL type, e.g. a map-in-map value to CONST_PTR_TO_MAP. Without it the register keeps base type PTR_TO_MAP_VALUE and check_map_access() treats it as raw data. Because the helper path skipped that step, an un-narrowed map-of-maps value could be passed to a nullable helper mem argument (e.g. bpf_csum_diff()) and read as bytes, leaking the inner map descriptor (a kernel pointer). The kfunc path already rejected the same program. Handle the possibly-NULL pointer in the shared mem-argument checking so helper and kfunc arguments are verified the same way, and drop the now redundant check_kfunc_mem_size_reg() wrapper. Both paths now reject an un-narrowed map-in-map value used as memory. Signed-off-by: Amery Hung --- kernel/bpf/verifier.c | 49 +++++++++++++++++++------------------------ 1 file changed, 22 insertions(+), 27 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 29d45636c28b..6520742d51b5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6873,7 +6873,14 @@ static int check_mem_size_reg(struct bpf_verifier_env *env, bool zero_size_allowed, struct bpf_call_arg_meta *meta) { - int err; + bool may_be_null = type_may_be_null(mem_reg->type); + struct bpf_reg_state saved_reg; + int err = 0; + + if (may_be_null) { + saved_reg = *mem_reg; + mark_ptr_not_null_reg(mem_reg); + } /* This is used to refine r0 return value bounds for helpers * that enforce this value as an upper bound on return values. @@ -6910,8 +6917,14 @@ static int check_mem_size_reg(struct bpf_verifier_env *env, reg_arg_name(env, size_argno)); return -EACCES; } - err = check_helper_mem_access(env, mem_reg, mem_argno, reg_umax(size_reg), - access_type, zero_size_allowed, meta); + + if (access_type & BPF_READ) + err = check_helper_mem_access(env, mem_reg, mem_argno, reg_umax(size_reg), + BPF_READ, zero_size_allowed, meta); + if (!err && access_type & BPF_WRITE) + err = check_helper_mem_access(env, mem_reg, mem_argno, reg_umax(size_reg), + BPF_WRITE, zero_size_allowed, meta); + if (!err) { int regno = reg_from_argno(size_argno); @@ -6920,6 +6933,10 @@ static int check_mem_size_reg(struct bpf_verifier_env *env, else err = mark_stack_arg_precision(env, arg_idx_from_argno(size_argno)); } + + if (may_be_null) + *mem_reg = saved_reg; + return err; } @@ -6993,28 +7010,6 @@ static int process_const_alloc_mem_size(struct bpf_verifier_env *env, struct bpf return 0; } -static int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *mem_reg, - struct bpf_reg_state *size_reg, argno_t mem_argno, - argno_t size_argno, struct bpf_call_arg_meta *meta) -{ - bool may_be_null = type_may_be_null(mem_reg->type); - struct bpf_reg_state saved_reg; - int err; - - if (may_be_null) { - saved_reg = *mem_reg; - mark_ptr_not_null_reg(mem_reg); - } - - err = check_mem_size_reg(env, mem_reg, size_reg, mem_argno, size_argno, BPF_READ, true, meta); - err = err ?: check_mem_size_reg(env, mem_reg, size_reg, mem_argno, size_argno, BPF_WRITE, true, meta); - - if (may_be_null) - *mem_reg = saved_reg; - - return err; -} - enum { PROCESS_SPIN_LOCK = (1 << 0), PROCESS_RES_LOCK = (1 << 1), @@ -12421,8 +12416,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_me argno_t next_argno = argno_from_arg(i + 2); if (!bpf_register_is_null(buff_reg) || !is_kfunc_arg_nullable(meta->btf, buff_arg)) { - ret = check_kfunc_mem_size_reg(env, buff_reg, size_reg, - argno, next_argno, meta); + ret = check_mem_size_reg(env, buff_reg, size_reg, argno, next_argno, + BPF_READ | BPF_WRITE, true, meta); if (ret < 0) { verbose(env, "%s and ", reg_arg_name(env, argno)); verbose(env, "%s memory, len pair leads to invalid memory access\n", -- 2.52.0