From patchwork Thu Jul 25 23:47:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Song Liu X-Patchwork-Id: 13742215 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 3787E1448EF; Thu, 25 Jul 2024 23:47:25 +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=1721951246; cv=none; b=FsO7pUNJQF4vwX3hHkEvxe9KgsOgjNqk3qERMUbM3gFmLord3K6QC4myvZM1yitW19aXOFRCHymrOZSDYjkoI1bMYEHSU1mXmV13U/q4jQ202KUUQehNh6a0JaXMyte+ZaCII1Klc+yr60PusP5tvO7SIv5bV4vPPc4Ua7ZByWs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721951246; c=relaxed/simple; bh=0UKtj6o3RWTCtZZLR5vBaT2vQGLsXGl2qOxqirhhQiw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XfCTuZPiy4rQx3ln+tbCNufpcgSMz3Uqz7P3EsHQBaPBtI0jy5zlZSdIQ5cO/8cw6cZB5/39IF9kZQ2kvSn5ozs0bHZ3aHYsgHeRgle26BVwVtm/Fmb0mk/zeOoRQN1HehTgCSFIS7nwLckkm2IAeCeMGRjJO3fiUd9/I5kgKiQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JxckO7u+; 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="JxckO7u+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 812A0C116B1; Thu, 25 Jul 2024 23:47:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721951245; bh=0UKtj6o3RWTCtZZLR5vBaT2vQGLsXGl2qOxqirhhQiw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JxckO7u+VhnbKiZ5TRGo7/l/3q0LnWJxFnUx+UcuOuNLVQgRWwgq8HRnCye+Fvc71 1rEY0xENW7E7XBj92Qix13qJD+1Gfxnzi7s/xkjaGeLoAHcsUmcIOsnzRFqKLToXfH 9cYT0/c0b91blB3wRRIrEiQWbg1ps4XHaMyz+nLaucH47P2Fu9F81WN9ufaWAWK6iV IooSLNHcieZ+/e4JV061cC89RcgZmOm7YlMcroYJrDCcU7jqVL8Bxn0WyUSN/WOkOm nsD6jqCXMBlbVlhiGUep4fmNA8fUVaBuN9OkJxAevTbkEmekytJ+H9A9ijkeDfywTG rR0Gzg+xhOaxw== From: Song Liu To: bpf@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@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, Song Liu Subject: [PATCH bpf-next 1/2] bpf: Add kfunc bpf_get_dentry_xattr() to read xattr from dentry Date: Thu, 25 Jul 2024 16:47:05 -0700 Message-ID: <20240725234706.655613-2-song@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240725234706.655613-1-song@kernel.org> References: <20240725234706.655613-1-song@kernel.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The primary use case here is to read xattr for directories from BPF programs. This feature enables tagging all the files in a directory with a xattr on the directory. More specifically, starting from LSM hook security_file_open(), we can read xattr of the file's parent directories. To have referenced access to dentry, a few more kfuncs are added: - bpf_file_dentry - bpf_dget_parent - bpf_dput Both bpf_file_dentry and bpf_dget_parent take a reference to the dentry (KF_ACQUIRE), which has to be released by bpf_dput (KF_RELEASE). This makes sure only trusted pointers (KF_TRUSTED_ARGS) can be used for the dentry. Note that, file_dentry() doesn't take reference to the dentry, but bpf_file_dentry() does. Signed-off-by: Song Liu --- kernel/trace/bpf_trace.c | 60 ++++++++++++++++++++++++++++++++++------ 1 file changed, 51 insertions(+), 9 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index cd098846e251..b8e6eeabb773 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1443,22 +1443,21 @@ late_initcall(bpf_key_sig_kfuncs_init); __bpf_kfunc_start_defs(); /** - * bpf_get_file_xattr - get xattr of a file - * @file: file to get xattr from + * bpf_get_dentry_xattr - get xattr of a dentry + * @dentry: dentry to get xattr from * @name__str: name of the xattr * @value_p: output buffer of the xattr value * - * Get xattr *name__str* of *file* and store the output in *value_ptr*. + * Get xattr *name__str* of *dentry* 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 *value_p) +__bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str, + struct bpf_dynptr *value_p) { struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p; - struct dentry *dentry; u32 value_len; void *value; int ret; @@ -1471,20 +1470,63 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str, if (!value) return -EINVAL; - dentry = file_dentry(file); ret = inode_permission(&nop_mnt_idmap, dentry->d_inode, MAY_READ); if (ret) return ret; return __vfs_getxattr(dentry, dentry->d_inode, name__str, value, value_len); } +/** + * bpf_get_file_xattr - get xattr of a file + * @file: file to get xattr from + * @name__str: name of the xattr + * @value_p: 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 *value_p) +{ + struct dentry *dentry; + + dentry = file_dentry(file); + return bpf_get_dentry_xattr(dentry, name__str, value_p); +} + +__bpf_kfunc struct dentry *bpf_file_dentry(const struct file *file) +{ + /* file_dentry() does not hold reference to the dentry. We add a + * dget() here so that we can add KF_ACQUIRE flag to + * bpf_file_dentry(). + */ + return dget(file_dentry(file)); +} + +__bpf_kfunc struct dentry *bpf_dget_parent(struct dentry *dentry) +{ + return dget_parent(dentry); +} + +__bpf_kfunc void bpf_dput(struct dentry *dentry) +{ + return dput(dentry); +} + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(fs_kfunc_set_ids) +BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS) BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, bpf_file_dentry, KF_TRUSTED_ARGS | KF_ACQUIRE) +BTF_ID_FLAGS(func, bpf_dget_parent, KF_TRUSTED_ARGS | KF_ACQUIRE) +BTF_ID_FLAGS(func, bpf_dput, KF_RELEASE) BTF_KFUNCS_END(fs_kfunc_set_ids) -static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id) +static int fs_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id) { if (!btf_id_set8_contains(&fs_kfunc_set_ids, kfunc_id)) return 0; @@ -1496,7 +1538,7 @@ static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id) static const struct btf_kfunc_id_set bpf_fs_kfunc_set = { .owner = THIS_MODULE, .set = &fs_kfunc_set_ids, - .filter = bpf_get_file_xattr_filter, + .filter = fs_kfunc_filter, }; static int __init bpf_fs_kfuncs_init(void)