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 E994A1E521D; Tue, 17 Jun 2025 06:11:26 +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=1750140687; cv=none; b=mgwNS/jvPRwGrk9hv07zFLEmaY+HKrgOuSzGCou/iSupu+bbuWehmWTPRxJcQhRCZH1o4wcCR1t6aSi+LoOsy2Oa9Ndx2R7NriYtuYYT5olEraUOiNK48tVgxQL7Bw1mKhlMTgAHNSYh5SGA2UJKLfi0/xqlQ2l/DDbGnCkLYa8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750140687; c=relaxed/simple; bh=RgJWHD65/lLqLRRj/mZf66iDcTZ9KMomSVgLP6/ZWFs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=pOW2pc/3riDTILLEoiug0tX9QpPDXB/1xMCGmtuQR333gzVk/ZExEzR5q7X1DPmqfg4GgR9yYqr0mcHQ6EPvxxud+sOr6CjJWuNuQyRwoQkE+ggv9yOjip8FVIP+y52bDnR+zAJ2FQo5ZkNDT2xN1czhXqGa0Jqd4yc9MT++t9w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q3xJYa2D; 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="Q3xJYa2D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9011C4CEE3; Tue, 17 Jun 2025 06:11:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750140686; bh=RgJWHD65/lLqLRRj/mZf66iDcTZ9KMomSVgLP6/ZWFs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Q3xJYa2Dx37asskvhJcEb2wXZaSzAH1DPhKkXRyClSTWR+He5ZalWkkP7ONdMuPEK T7PvSxP+V+/Z/yV2GSoS7eIQVWGD3FUNbzcLXDV9r/rhPoAXdzRjzvRK/3kCDyfnGS ITi6x7ck1nOFgauZtRPytsFUxynAz04qzpfogCKWvLhbr5aRU0B0CobchHRRDLqwvO 8u47+EzNNuDHekc57FWyRrBlIMDV62qJNpObWQsWcusYvY3qf6ikHPxX18ktFNLYZs ehEhqK4gzNDPbPG7Y5w336pJ1Vu+XbXeNMDtSFjqYRiCgthqniAdWtXkJUw6Xd5KkO kEMRkfVMLBUNg== 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, m@maowtm.org, neil@brown.name, Song Liu Subject: [PATCH v5 bpf-next 1/5] namei: Introduce new helper function path_walk_parent() Date: Mon, 16 Jun 2025 23:11:12 -0700 Message-ID: <20250617061116.3681325-2-song@kernel.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250617061116.3681325-1-song@kernel.org> References: <20250617061116.3681325-1-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 This helper walks an input path to its parent. Logic are added to handle walking across mount tree. This will be used by landlock, and BPF LSM. Suggested-by: Neil Brown Signed-off-by: Song Liu --- fs/namei.c | 95 +++++++++++++++++++++++++++++++++++-------- include/linux/namei.h | 2 + 2 files changed, 79 insertions(+), 18 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 4bb889fc980b..d0557c0b5cc8 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2048,36 +2048,95 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd) return nd->path.dentry; } -static struct dentry *follow_dotdot(struct nameidata *nd) +/** + * __path_walk_parent - Find the parent of the given struct path + * @path - The struct path to start from + * @root - A struct path which serves as a boundary not to be crosses. + * - If @root is zero'ed, walk all the way to global root. + * @flags - Some LOOKUP_ flags. + * + * Find and return the dentry for the parent of the given path + * (mount/dentry). If the given path is the root of a mounted tree, it + * is first updated to the mount point on which that tree is mounted. + * + * If %LOOKUP_NO_XDEV is given, then *after* the path is updated to a new + * mount, the error EXDEV is returned. + * + * If no parent can be found, either because the tree is not mounted or + * because the @path matches the @root, then @path->dentry is returned + * unless @flags contains %LOOKUP_BENEATH, in which case -EXDEV is returned. + * + * Returns: either an ERR_PTR() or the chosen parent which will have had + * the refcount incremented. + */ +static struct dentry *__path_walk_parent(struct path *path, const struct path *root, int flags) { - struct dentry *parent; - - if (path_equal(&nd->path, &nd->root)) + if (path_equal(path, root)) goto in_root; - if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) { - struct path path; + if (unlikely(path->dentry == path->mnt->mnt_root)) { + struct path new_path; - if (!choose_mountpoint(real_mount(nd->path.mnt), - &nd->root, &path)) + if (!choose_mountpoint(real_mount(path->mnt), + root, &new_path)) goto in_root; - path_put(&nd->path); - nd->path = path; - nd->inode = path.dentry->d_inode; - if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + path_put(path); + *path = new_path; + if (unlikely(flags & LOOKUP_NO_XDEV)) return ERR_PTR(-EXDEV); } /* rare case of legitimate dget_parent()... */ - parent = dget_parent(nd->path.dentry); + return dget_parent(path->dentry); + +in_root: + if (unlikely(flags & LOOKUP_BENEATH)) + return ERR_PTR(-EXDEV); + return dget(path->dentry); +} + +/** + * path_walk_parent - Walk to the parent of path + * @path: input and output path. + * @root: root of the path walk, do not go beyond this root. If @root is + * zero'ed, walk all the way to real root. + * + * Given a path, find the parent path. Replace @path with the parent path. + * If we were already at the real root or a disconnected root, @path is + * not changed. + * + * Returns: + * 0 - if @path is updated to its parent. + * <0 - if @path is already the root (real root or @root). + */ +int path_walk_parent(struct path *path, const struct path *root) +{ + struct dentry *parent; + + parent = __path_walk_parent(path, root, LOOKUP_BENEATH); + + if (IS_ERR(parent)) + return PTR_ERR(parent); + + if (parent == path->dentry) { + dput(parent); + return -ENOENT; + } + dput(path->dentry); + path->dentry = parent; + return 0; +} + +static struct dentry *follow_dotdot(struct nameidata *nd) +{ + struct dentry *parent = __path_walk_parent(&nd->path, &nd->root, nd->flags); + + if (IS_ERR(parent)) + return parent; if (unlikely(!path_connected(nd->path.mnt, parent))) { dput(parent); return ERR_PTR(-ENOENT); } + nd->inode = nd->path.dentry->d_inode; return parent; - -in_root: - if (unlikely(nd->flags & LOOKUP_BENEATH)) - return ERR_PTR(-EXDEV); - return dget(nd->path.dentry); } static const char *handle_dots(struct nameidata *nd, int type) diff --git a/include/linux/namei.h b/include/linux/namei.h index 5d085428e471..ca68fa4089e0 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -85,6 +85,8 @@ extern int follow_down_one(struct path *); extern int follow_down(struct path *path, unsigned int flags); extern int follow_up(struct path *); +int path_walk_parent(struct path *path, const struct path *root); + extern struct dentry *lock_rename(struct dentry *, struct dentry *); extern struct dentry *lock_rename_child(struct dentry *, struct dentry *); extern void unlock_rename(struct dentry *, struct dentry *); -- 2.47.1