From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BF283A6B66; Thu, 17 Sep 2026 15:26:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789658821; cv=none; b=lnhmH7JcL6QKPmIFT+0OyIuZ2TrtaK+xtrMdBs/rtgwSkQUWLyWQUhR4xv3Bz1RzJqKWyUPoH9cZuaQk2bLn9IRoEGcveMebNlKZ/W+joK4aGMExsn8tmgZeJs+ZFi7nhD9uJwmZ4LEHrr7zS68otq16RWo2X6Ovg+bbXEF4juY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789658821; c=relaxed/simple; bh=X49b+NE97QXPpesVO16BxOHSFQcs7Sh3CjvXpiw7qik=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=P27nogubjYWzqz9W5arnnt7pNegBo7oH3frr7/KL+ggllrda5yzurvlK5ivILx9y7Ti0dAz9XI6wLrOLwhnh98mnOJq9ETQiDQSXXClEvg5HKvx0rFg77bFYgSjr1hGwchny9NSo4GAcGlqWqFTtO9r/d6aJvFzpc4wB5na8ZZ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ePEcvGHK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ePEcvGHK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DC4C1F000FF; Thu, 17 Sep 2026 15:26:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789658814; bh=b/MhsAW7bXltJQwDUXTdPWZbNwSVlGT2cpZWDpz8uGw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ePEcvGHKmiBdVy/PCDBJvbcS2bnAHD3XX1zJ/yTBHs8r1NLFZqPNjCUHLedBYEa/I 20JWX2P6i8bSEkuBoSfOVIg+DeN6yNz1lA6yUZ1uLaAhseYTk6On9JSjJmsoK0JqQI EcOAFjJf4bOzaYQX/RtiGcUTjzSj5zPqx9ZHMtyI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Nicholas Carlini , Eduard Zingerman , Alexei Starovoitov , Sasha Levin Subject: [PATCH 7.2 049/733] bpf: check_cond_jmp_op(): properly infer if register is null Date: Thu, 17 Sep 2026 16:05:57 +0100 Message-ID: <20260917151352.000589516@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151350.597953846@linuxfoundation.org> References: <20260917151350.597953846@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eduard Zingerman [ Upstream commit d3ef6c097ba078e1f8c7239d76a0ce8b61e75095 ] Nicholas Carlini reported a bug when verifier can incorrectly infer that a pointer is non-null. The bug occurs when two pointers are compared and one of them has a type w/o PTR_MAYBE_NULL flag, but which allows a value to be NULL at runtime. Here is an example: // `a` is PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED // `a` is 0 at runtime. // `b` is PTR_TO_MAP_VALUE | PTR_MAYBE_NULL void *a = bpf_rdonly_cast(0, 0); int *b = bpf_map_lookup_elem(...); if (a == b) *b = 42; // verifier does not catch null pointer dereference This happens because of a special case in check_cond_jmp_op(), which attempts to strip PTR_MAYBE_NULL flags from pointer types, when processing comparisons like `rA == rB`, if either rA or rB can't be null. The non-null property is derived based on the absence of PTR_MAYBE_NULL flag on rA's or rB's type. But that is not sufficient for types like PTR_TO_MEM, as in the example. This patch replaces type_may_be_null() call with reg_not_null(), which contains an allowlist of types for which absence of PTR_MAYBE_NULL actually means that the value can't be NULL at runtime. At the moment, the list in the reg_not_null() omits two types for which PTR_MAYBE_NULL is applicable: PTR_TO_XDP_SOCK and PTR_TO_BUF. In order to remain backward compatible, and assuming that only comparison between pointers of the same type makes sense, this commit extends reg_not_null(). W/o such an extension e.g. verifier_jeq_infer_not_null/null_ptr_to_map_value fails. reg_not_null() can be extended further, but I deem that out of scope for the fix at hand. Explicit base_type(...) != PTR_TO_BTF_ID checks in the check_cond_jmp_op() can be removed with migration to reg_not_null(), but that is a behavioural change, as the special case would start matching for PTR_TO_BTF_ID that is also is_trusted_reg(). I omit the behavioural change from this commit. Fixes: befae75856ab ("bpf: propagate nullness information for reg to reg comparisons") Suggested-by: Nicholas Carlini Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20260826-bug-029-bad-non-null-inference-v2-1-136789ace9e9@localhost Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 03187bab806a7..59f12ba70eb6e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -370,6 +370,8 @@ static bool reg_not_null(struct bpf_verifier_env *env, const struct bpf_reg_stat type = base_type(type); return type == PTR_TO_SOCKET || type == PTR_TO_TCP_SOCK || + type == PTR_TO_XDP_SOCK || + type == PTR_TO_BUF || type == PTR_TO_MAP_VALUE || type == PTR_TO_MAP_KEY || type == PTR_TO_SOCK_COMMON || @@ -16173,7 +16175,6 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, */ if (!is_jmp32 && BPF_SRC(insn->code) == BPF_X && __is_pointer_value(false, src_reg) && __is_pointer_value(false, dst_reg) && - type_may_be_null(src_reg->type) != type_may_be_null(dst_reg->type) && base_type(src_reg->type) != PTR_TO_BTF_ID && base_type(dst_reg->type) != PTR_TO_BTF_ID) { eq_branch_regs = NULL; @@ -16189,9 +16190,11 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, break; } if (eq_branch_regs) { - if (type_may_be_null(src_reg->type)) + /* src == dst && dst != NULL => src != NULL */ + if (reg_not_null(env, dst_reg) && type_may_be_null(src_reg->type)) mark_ptr_not_null_reg(&eq_branch_regs[insn->src_reg]); - else + /* src == dst && src != NULL => dst != NULL */ + if (reg_not_null(env, src_reg) && type_may_be_null(dst_reg->type)) mark_ptr_not_null_reg(&eq_branch_regs[insn->dst_reg]); } } -- 2.53.0