From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 AFFE9136348; Mon, 23 Jun 2025 06:39:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750660753; cv=none; b=m2MDFWlNuFVBDhd7Anlo0v6FkbUjKs+uEiSOXl/vxO/euLHNJzqIGZEefQfTJQW6XYj0YpkBd1T6YQxnwvS4FKEMjQu9U4Z4IaHw/dKsLpdkeQHcuShUTp8L78Mc4uvj3Kv34ndhfXSyHWMrSSqX2Y0hdkaOFUcbSnDKKWTj4Lc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750660753; c=relaxed/simple; bh=0Jo3+klb7sn+Ci+xFRJd1JpVX2+HyuPav+mXSbeFpyg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZuDadEBo064G75Lza65Yb7a/IGRSnyZZ9x86FG7K9jgV+Iv5jo+BcwGvkJo5+kf2Uq4j7o+/4DiHp0HMVqIRDG5b9xarjSXJn2mnxhJtoO0Nyaf436PwU0TLj55CQYIo8SVymTi93RalPungYBOlUeawxpP5mFR7F+TJ4r3Fzy8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HLuuMss4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HLuuMss4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B20B5C4CEED; Mon, 23 Jun 2025 06:39:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750660753; bh=0Jo3+klb7sn+Ci+xFRJd1JpVX2+HyuPav+mXSbeFpyg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HLuuMss4M9D4QRBc7/VWf6NGL+3i7HiOgDoJxTM02s54Z1DxwcPzujdwTg15qjA2E EJHg/UuRL3X2JBYUNyhVSTqDUxzrdTuUwE09KZFixpnBy0Bxn7iY59iLo0kbpbZjGp ljSngmZWE+Om3hkNE7/zMnvuJN5dPiR8hM4UeL4cX0cBSX6v2jiL/R3SuFYkHflpfN +1TJXx7LEYUj2RNIDov++fvdIfRcKDGDuowbmh1uTqoS9EDDdqpjZSG1CP4sfDjCwu WGwPQSv2/0GfNbuqyr5W0IN668U/V89TgZxzXWCfzOocEKqapFcotfFa2NKZNpQYRe t+qpQYvK2oHug== From: Song Liu To: bpf@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Cc: 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, gregkh@linuxfoundation.org, tj@kernel.org, daan.j.demeyer@gmail.com, Song Liu Subject: [PATCH v3 bpf-next 2/4] bpf: Introduce bpf_cgroup_read_xattr to read xattr of cgroup's node Date: Sun, 22 Jun 2025 23:38:52 -0700 Message-ID: <20250623063854.1896364-3-song@kernel.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250623063854.1896364-1-song@kernel.org> References: <20250623063854.1896364-1-song@kernel.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit BPF programs, such as LSM and sched_ext, would benefit from tags on cgroups. One common practice to apply such tags is to set xattrs on cgroupfs folders. Introduce kfunc bpf_cgroup_read_xattr, which allows reading cgroup's xattr. Note that, we already have bpf_get_[file|dentry]_xattr. However, these two APIs are not ideal for reading cgroupfs xattrs, because: 1) These two APIs only works in sleepable contexts; 2) There is no kfunc that matches current cgroup to cgroupfs dentry. bpf_cgroup_read_xattr is generic and can be useful for many program types. It is also safe, because it requires trusted or rcu protected argument (KF_RCU). Therefore, we make it available to all program types. Signed-off-by: Song Liu Acked-by: Tejun Heo --- fs/bpf_fs_kfuncs.c | 34 ++++++++++++++++++++++++++++++++++ kernel/bpf/helpers.c | 3 +++ 2 files changed, 37 insertions(+) diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c index 08412532db1b..1e36a12b88f7 100644 --- a/fs/bpf_fs_kfuncs.c +++ b/fs/bpf_fs_kfuncs.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include @@ -322,6 +323,39 @@ __bpf_kfunc int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name_ return ret; } +#ifdef CONFIG_CGROUPS +/** + * bpf_cgroup_read_xattr - read xattr of a cgroup's node in cgroupfs + * @cgroup: cgroup to get xattr from + * @name__str: name of the xattr + * @value_p: output buffer of the xattr value + * + * Get xattr *name__str* of *cgroup* and store the output in *value_ptr*. + * + * For security reasons, only *name__str* with prefix "user." is allowed. + * + * Return: length of the xattr value on success, a negative value on error. + */ +__bpf_kfunc int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str, + struct bpf_dynptr *value_p) +{ + struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p; + u32 value_len; + void *value; + + /* Only allow reading "user.*" xattrs */ + if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) + return -EPERM; + + value_len = __bpf_dynptr_size(value_ptr); + value = __bpf_dynptr_data_rw(value_ptr, value_len); + if (!value) + return -EINVAL; + + return kernfs_xattr_get(cgroup->kn, name__str, value, value_len); +} +#endif /* CONFIG_CGROUPS */ + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(bpf_fs_kfunc_set_ids) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index b71e428ad936..9ff1b4090289 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) +#ifdef CONFIG_CGROUPS +BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU) +#endif BTF_KFUNCS_END(common_btf_ids) static const struct btf_kfunc_id_set common_kfunc_set = { -- 2.47.1