From patchwork Thu Nov 2 16:54:27 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Song Liu X-Patchwork-Id: 13444002 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 E2D9918E17; Thu, 2 Nov 2023 16:55:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mt5XaQ6v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0855CC433C8; Thu, 2 Nov 2023 16:55:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1698944104; bh=BjCSFY2LUDqve65p9mjPqLiMd/5wZBoOi6ScY3R1LwM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Mt5XaQ6vP/D6J672q6no+tZXJV+xc8JP7HYnsEq3r2GAGCi6v2+IeaxjJLy4thvhO sK/FRDXOMbNcAIMhSqm5lX3yiqTrezkmB0OSaYBauxFhP/oJDIwLKbkH7//DYuoNZ6 ePDFePDAhxW6E4s3C2Nw7gfMcup5bWBHvgSgrQbHpGm+K5TdaXYiB9j3Rcq0M2SxRX 3Z1Pswc5WmkeDiSV4C54Wo8OCu5O8T/n6DgAzphbQLwPEz9vpCQ3LfpPJOSoc0/80P KELlKaVigtKK18PmVarGAjIUNkB3xoHjNfxhKhhD3eZnFjE9D7C9xvCeD3buERAl9c i56OJVjoF3o0w== From: Song Liu To: bpf@vger.kernel.org, fsverity@lists.linux.dev Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, kernel-team@meta.com, ebiggers@kernel.org, tytso@mit.edu, roberto.sassu@huaweicloud.com, kpsingh@kernel.org, Song Liu Subject: [PATCH v7 bpf-next 4/9] bpf: Add kfunc bpf_get_file_xattr Date: Thu, 2 Nov 2023 09:54:27 -0700 Message-Id: <20231102165432.1769965-5-song@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231102165432.1769965-1-song@kernel.org> References: <20231102165432.1769965-1-song@kernel.org> Precedence: bulk X-Mailing-List: fsverity@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 It is common practice for security solutions to store tags/labels in xattrs. To implement similar functionalities in BPF LSM, add new kfunc bpf_get_file_xattr(). The first use case of bpf_get_file_xattr() is to implement file verifications with asymmetric keys. Specificially, security applications could use fsverity for file hashes and use xattr to store file signatures. (kfunc for fsverity hash will be added in a separate commit.) Currently, only xattrs with "user." prefix can be read with kfunc bpf_get_file_xattr(). As use cases evolve, we may add a dedicated prefix for bpf_get_file_xattr(). To avoid recursion, bpf_get_file_xattr can be only called from LSM hooks. Signed-off-by: Song Liu --- kernel/trace/bpf_trace.c | 64 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 2626706b6387..19f3e5fddfe6 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -24,6 +24,7 @@ #include #include #include +#include #include @@ -1436,6 +1437,69 @@ static int __init bpf_key_sig_kfuncs_init(void) late_initcall(bpf_key_sig_kfuncs_init); #endif /* CONFIG_KEYS */ +/* filesystem kfuncs */ +__diag_push(); +__diag_ignore_all("-Wmissing-prototypes", + "kfuncs which will be used in BPF programs"); + +/** + * bpf_get_file_xattr - get xattr of a file + * @file: file to get xattr from + * @name__str: name of the xattr + * @value_ptr: output buffer of the xattr value + * + * Get xattr *name__str* of *file* and store the output in *value_ptr*. + * + * For security reasons, only *name__str* with prefix "user." is allowed. + * + * Return: 0 on success, a negative value on error. + */ +__bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str, + struct bpf_dynptr_kern *value_ptr) +{ + struct dentry *dentry; + void *value; + + if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) + return -EPERM; + + value = bpf_dynptr_slice_rdwr(value_ptr, 0, NULL, 0); + if (IS_ERR_OR_NULL(value)) + return PTR_ERR(value); + + dentry = file_dentry(file); + return __vfs_getxattr(dentry, dentry->d_inode, name__str, + value, __bpf_dynptr_size(value_ptr)); +} + +__diag_pop(); + +BTF_SET8_START(fs_kfunc_set_ids) +BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS) +BTF_SET8_END(fs_kfunc_set_ids) + +static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id) +{ + if (!btf_id_set8_contains(&fs_kfunc_set_ids, kfunc_id)) + return 0; + + /* Only allow to attach from LSM hooks, to avoid recursion */ + return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; +} + +const struct btf_kfunc_id_set bpf_fs_kfunc_set = { + .owner = THIS_MODULE, + .set = &fs_kfunc_set_ids, + .filter = bpf_get_file_xattr_filter, +}; + +static int __init bpf_fs_kfuncs_init(void) +{ + return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set); +} + +late_initcall(bpf_fs_kfuncs_init); + static const struct bpf_func_proto * bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) {