From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 4288121C16D for ; Tue, 3 Jun 2025 20:49:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748983802; cv=none; b=rEEgNGHYJ67kLheZ/9VwzCx+2jcE9cisN+hL5Gt3VhbibnY97aQiakfUk1VRexHIfcJiWcHL9TlKsSATKa3HKRct2Wvs6/6sYOZcC7NVU5TRHk9qGx8OKBGmZHVUY6w+MkuZiYqQhJze7htdMemkENyxK01MY7oUZxfHcluAe/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748983802; c=relaxed/simple; bh=j9OUWrhChf7ZQCsdoqnA29xM4WW996oqQ1Kht5NiaRI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=r/2M1Z+y7yu4m3U+alTDZsE3BzrDZejzeRDaKyuHLMefiZ1WB7s7Dr+rB1VJyutGLDb2BcjgikreXUv8cJuUJb6a7F16A2xciek5sflUrazceaEw5eaV5PBdxbd9dVgcEmNq5qYHLMJGuTimvQe242LFJsjGnWDH5jhTTf66gS4= 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=KB2rPxdM; arc=none smtp.client-ip=91.218.175.179 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="KB2rPxdM" Message-ID: <4c60e0e4-0bb8-4ae4-b7c3-f29af926f6a0@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1748983795; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AYDczDkAWGO7hhWYMWNKnea7MYkw9912XrfEX61Dh/U=; b=KB2rPxdMXmrNDx+/PRWF+SZ0Dq9rGGghN/OMmDeHZb7kzLHmtNXE/N1xPsQ7BN82Nq5CVI oRoiTZXpBOyHUrBLMPr7ZBLs2dUdMknaz/LQDr5fWYnqy4ysEd02nzyawtblVs5UchB8aG fEPIKdVGWtijMCNEcSu6t2AyXcuPa9M= Date: Tue, 3 Jun 2025 13:49:47 -0700 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 bpf-next 3/4] bpf: Introduce path iterator Content-Language: en-GB To: Andrii Nakryiko , Song Liu Cc: bpf@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, kernel-team@meta.com, andrii@kernel.org, eddyz87@gmail.com, ast@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, kpsingh@kernel.org, mattbobrowski@google.com, amir73il@gmail.com, repnop@google.com, jlayton@kernel.org, josef@toxicpanda.com, mic@digikod.net, gnoack@google.com, m@maowtm.org References: <20250603065920.3404510-1-song@kernel.org> <20250603065920.3404510-4-song@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/3/25 11:40 AM, Andrii Nakryiko wrote: > On Mon, Jun 2, 2025 at 11:59 PM Song Liu wrote: >> Introduce a path iterator, which reliably walk a struct path toward >> the root. This path iterator is based on path_walk_parent. A fixed >> zero'ed root is passed to path_walk_parent(). Therefore, unless the >> user terminates it earlier, the iterator will terminate at the real >> root. >> >> Signed-off-by: Song Liu >> --- >> kernel/bpf/Makefile | 1 + >> kernel/bpf/helpers.c | 3 +++ >> kernel/bpf/path_iter.c | 58 ++++++++++++++++++++++++++++++++++++++++++ >> kernel/bpf/verifier.c | 5 ++++ >> 4 files changed, 67 insertions(+) >> create mode 100644 kernel/bpf/path_iter.c >> >> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile >> index 3a335c50e6e3..454a650d934e 100644 >> --- a/kernel/bpf/Makefile >> +++ b/kernel/bpf/Makefile >> @@ -56,6 +56,7 @@ obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o >> ifeq ($(CONFIG_DMA_SHARED_BUFFER),y) >> obj-$(CONFIG_BPF_SYSCALL) += dmabuf_iter.o >> endif >> +obj-$(CONFIG_BPF_SYSCALL) += path_iter.o >> >> CFLAGS_REMOVE_percpu_freelist.o = $(CC_FLAGS_FTRACE) >> CFLAGS_REMOVE_bpf_lru_list.o = $(CC_FLAGS_FTRACE) >> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c >> index b71e428ad936..b190c78e40f6 100644 >> --- a/kernel/bpf/helpers.c >> +++ b/kernel/bpf/helpers.c >> @@ -3397,6 +3397,9 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPAB >> BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE) >> #endif >> BTF_ID_FLAGS(func, __bpf_trap) >> +BTF_ID_FLAGS(func, bpf_iter_path_new, KF_ITER_NEW | KF_SLEEPABLE) >> +BTF_ID_FLAGS(func, bpf_iter_path_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPABLE) >> +BTF_ID_FLAGS(func, bpf_iter_path_destroy, KF_ITER_DESTROY | KF_SLEEPABLE) >> BTF_KFUNCS_END(common_btf_ids) >> >> static const struct btf_kfunc_id_set common_kfunc_set = { >> diff --git a/kernel/bpf/path_iter.c b/kernel/bpf/path_iter.c >> new file mode 100644 >> index 000000000000..0d972ec84beb >> --- /dev/null >> +++ b/kernel/bpf/path_iter.c >> @@ -0,0 +1,58 @@ >> +// SPDX-License-Identifier: GPL-2.0-only >> +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */ >> +#include >> +#include >> +#include >> +#include >> + >> +/* open-coded iterator */ >> +struct bpf_iter_path { >> + __u64 __opaque[3]; >> +} __aligned(8); >> + >> +struct bpf_iter_path_kern { >> + struct path path; >> + __u64 flags; >> +} __aligned(8); >> + >> +__bpf_kfunc_start_defs(); >> + >> +__bpf_kfunc int bpf_iter_path_new(struct bpf_iter_path *it, >> + struct path *start, >> + __u64 flags) >> +{ >> + struct bpf_iter_path_kern *kit = (void *)it; >> + >> + BUILD_BUG_ON(sizeof(*kit) > sizeof(*it)); >> + BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it)); >> + >> + if (flags) { >> + memset(&kit->path, 0, sizeof(struct path)); >> + return -EINVAL; >> + } >> + >> + kit->path = *start; >> + path_get(&kit->path); >> + kit->flags = flags; >> + >> + return 0; >> +} >> + >> +__bpf_kfunc struct path *bpf_iter_path_next(struct bpf_iter_path *it) >> +{ >> + struct bpf_iter_path_kern *kit = (void *)it; >> + struct path root = {}; >> + >> + if (!path_walk_parent(&kit->path, &root)) >> + return NULL; >> + return &kit->path; >> +} >> + >> +__bpf_kfunc void bpf_iter_path_destroy(struct bpf_iter_path *it) >> +{ >> + struct bpf_iter_path_kern *kit = (void *)it; >> + >> + path_put(&kit->path); > note, destroy() will be called even if construction of iterator fails > or we exhausted iterator. So you need to make sure that you have > bpf_iter_path state where you can detect that there is no path present > and skip path_put(). In rare cases, it is possible &kit->path address could be destroyed and reused, right? Maybe we need more state in kit to detect the change? > >> +} >> + >> +__bpf_kfunc_end_defs(); >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index a7d6e0c5928b..45b45cdfb223 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -7036,6 +7036,10 @@ BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket) { >> struct sock *sk; >> }; >> >> +BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path) { >> + struct dentry *dentry; >> +}; >> + >> static bool type_is_rcu(struct bpf_verifier_env *env, >> struct bpf_reg_state *reg, >> const char *field_name, u32 btf_id) >> @@ -7076,6 +7080,7 @@ static bool type_is_trusted_or_null(struct bpf_verifier_env *env, >> const char *field_name, u32 btf_id) >> { >> BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket)); >> + BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path)); >> >> return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id, >> "__safe_trusted_or_null"); >> -- >> 2.47.1 >>