From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 2AD01371D0A for ; Thu, 21 May 2026 03:24:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779333863; cv=none; b=imF92lzx6tmAQyoHJOTI78m5fIMB9BxxUXdCUWktuiXaPtWuev66hmf7hKiqRP8NGHC096+9AGBuuaZel580aRposNGLLnoo+aBBCZumE3OKY9NvMEHLspVzT6Es8oN5MtdOIwI3KpZJrV0xaeFnCVkjR+1IucQnC8z+eNIOpMk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779333863; c=relaxed/simple; bh=uTA/IPe0SD3xMXt47BGiypLhOKhs44rGXPEp3qX5o8Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RPBNWeN6PdXagpRHDjgAliKs6IAf4hlEpnnexJvn5tLAW2FxmSc1fqL+gDwo7SpRFR8nc2UZvqeXSryXcvA79hxOUo8FTRt0Dd9vWJQM9LU5KRzW98gcbgYB/yuSLRCY46H9JJ/b3RFZF05/6/ZCw3VH4CXU9Mxsnw3Sj+5tCcs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Q/ziLl55; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Q/ziLl55" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779333859; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EibCAjpYj8bsk5BcAAI7Zy4bc3E7PcZnr8SoDxq6ulc=; b=Q/ziLl55fMtz/TMzFoyk3a5EKDsGd1AFw0qH2POzV2eSOrImf4X0GLOIm43dLqybdwmCpb ZaMtCgS18bdvI4cQNslKfpVWPtOnV4t+ZAFqgSJPmkuIxtjiWUZDFscvgBo3BUuO+tUl2K rlJTfCBY4YPbTThDHShQgdBQ6NI279Q= From: Kaitao Cheng To: ast@kernel.org, corbet@lwn.net, martin.lau@linux.dev, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, chengkaitao@kylinos.cn, skhan@linuxfoundation.org, memxor@gmail.com Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, vmalik@redhat.com, linux-kselftest@vger.kernel.org Subject: [PATCH bpf-next v11 2/8] bpf: clear list node owner and unlink before drop Date: Thu, 21 May 2026 11:23:00 +0800 Message-ID: <20260521032306.97118-3-kaitao.cheng@linux.dev> In-Reply-To: <20260521032306.97118-1-kaitao.cheng@linux.dev> References: <20260521032306.97118-1-kaitao.cheng@linux.dev> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Kaitao Cheng The issue only becomes exposed once bpf_list_del() is available: callers can pass an arbitrary bpf_list_head and bpf_list_node pair, including nodes that are not actually linked to the supplied head, or nodes that outlive their original head after refcount-based retention. This was not practically reachable for callers restricted to pop-style helpers alone; bpf_list_del() widens the API surface. A failure mode appears when bpf_list_head_free() runs while a program still holds an independent refcount on a node (for example via bpf_refcount_acquire()). The list head value embedded in map memory can go away while the node object survives. If node->owner is left pointing at the old head address until drop completes, that pointer becomes stale. If a new bpf_list_head is later allocated at the same address and the stale node is passed to bpf_list_del(), the owner comparison can succeed even though the node is not really linked to the new head, and list_del_init() will follow bogus next/prev pointers with the risk of memory corruption. When draining a bpf_list_head, mark each node owner with BPF_PTR_POISON under the map spinlock while moving it to a private drain list, then list_del_init() the node and clear owner to NULL before calling __bpf_obj_drop_impl(). Concurrent readers therefore never observe a node that appears linked to a head while its list_head is inconsistent, and surviving refcounted nodes never retain a stale non-NULL owner. Signed-off-by: Kaitao Cheng --- kernel/bpf/helpers.c | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 094457c3e6d3..59855b434f0b 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2247,10 +2247,11 @@ EXPORT_SYMBOL_GPL(bpf_base_func_proto); void bpf_list_head_free(const struct btf_field *field, void *list_head, struct bpf_spin_lock *spin_lock) { - struct list_head *head = list_head, *orig_head = list_head; + struct list_head *head = list_head, drain, *pos, *n; BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct bpf_list_head)); BUILD_BUG_ON(__alignof__(struct list_head) > __alignof__(struct bpf_list_head)); + INIT_LIST_HEAD(&drain); /* Do the actual list draining outside the lock to not hold the lock for * too long, and also prevent deadlocks if tracing programs end up @@ -2261,20 +2262,30 @@ void bpf_list_head_free(const struct btf_field *field, void *list_head, __bpf_spin_lock_irqsave(spin_lock); if (!head->next || list_empty(head)) goto unlock; - head = head->next; + list_for_each_safe(pos, n, head) { + struct bpf_list_node_kern *node; + + node = container_of(pos, struct bpf_list_node_kern, list_head); + WRITE_ONCE(node->owner, BPF_PTR_POISON); + list_move_tail(pos, &drain); + } unlock: - INIT_LIST_HEAD(orig_head); + INIT_LIST_HEAD(head); __bpf_spin_unlock_irqrestore(spin_lock); - while (head != orig_head) { - void *obj = head; + while (!list_empty(&drain)) { + struct bpf_list_node_kern *node; - obj -= field->graph_root.node_offset; - head = head->next; + pos = drain.next; + node = container_of(pos, struct bpf_list_node_kern, list_head); + list_del_init(pos); + /* Ensure __bpf_list_add() sees the node as unlinked. */ + smp_store_release(&node->owner, NULL); /* The contained type can also have resources, including a * bpf_list_head which needs to be freed. */ - __bpf_obj_drop_impl(obj, field->graph_root.value_rec, false); + __bpf_obj_drop_impl((char *)pos - field->graph_root.node_offset, + field->graph_root.value_rec, false); } } -- 2.50.1 (Apple Git-155)