From patchwork Mon Mar 10 09:41:54 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 14009478 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 725C2225A36 for ; Mon, 10 Mar 2025 09:42:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741599752; cv=none; b=ea0GQlYhQMOLXP5VfYE23ZKg+zdUnPdXf5g3oXWdcZb/M6odIcV1eHul1Au5QLBuBwtdyFrZy0n1teolszACGh3zYXbIXyCzSJ3jS6q5XsPysMyfJo+DgLaQF151tlefhULX4LDsApV+d3YWSyuRutB1ajkCjTkVBo5F2g6ChEo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741599752; c=relaxed/simple; bh=6vtwEs+rHM1jWLym/vaXSW2BCT8cpdWZuotX4+2I2Vc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CzOyPC8mxCD1jRk7GPVRh8GNMeuac0g3scnI7YZe4oGSCBWBPC2Wu1BqkYoOsIGnRPSNjtFSygRkLJY1UWuYQPt0R6dvTRkVLdoIcZ8qmj9xYJkEOfSIPhh4pLoMOiArv3DhCw7yYQh4q3Px5/CQh3V8kUAwIty4k06i7tHsq+A= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZlCqvYLf; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZlCqvYLf" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741599749; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cRYHIcDjLcg4Vn95ha4RWQZUMP+5IMAoLBX9IqR4Ab4=; b=ZlCqvYLf5yHU8RAqeIKXoe8sI1rmd5m90ULsvXXeZ4zVakIqDyPxP5LYs9Ud9RT1fTnSXJ Lk9Dl4rWvdvOZDNuWbbBv1n/Hoy6SRuHeHl+kaodfq/WHqRE7vwRHmiBSL1rjwptuUBxPW IoFrr246SqYPpFkzQYNNZHj/dHH1mVg= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-295-eS1fX2frNM2QQtn-R6jD8Q-1; Mon, 10 Mar 2025 05:42:24 -0400 X-MC-Unique: eS1fX2frNM2QQtn-R6jD8Q-1 X-Mimecast-MFC-AGG-ID: eS1fX2frNM2QQtn-R6jD8Q_1741599743 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1987E19560B2; Mon, 10 Mar 2025 09:42:22 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.42.28.61]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 633A91800944; Mon, 10 Mar 2025 09:42:19 +0000 (UTC) From: David Howells To: Marc Dionne Cc: David Howells , Christian Brauner , linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Viro Subject: [PATCH v4 01/11] afs: Fix afs_atcell_get_link() to handle RCU pathwalk Date: Mon, 10 Mar 2025 09:41:54 +0000 Message-ID: <20250310094206.801057-2-dhowells@redhat.com> In-Reply-To: <20250310094206.801057-1-dhowells@redhat.com> References: <20250310094206.801057-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 The ->get_link() method may be entered under RCU pathwalk conditions (in which case, the dentry pointer is NULL). This is not taken account of by afs_atcell_get_link() and lockdep will complain when it tries to lock an rwsem. Fix this by marking net->ws_cell as __rcu and using RCU access macros on it and by making afs_atcell_get_link() just return a pointer to the name in RCU pathwalk without taking net->cells_lock or a ref on the cell as RCU will protect the name storage (the cell is already freed via call_rcu()). Fixes: 30bca65bbbae ("afs: Make /afs/@cell and /afs/.@cell symlinks") Reported-by: Alexander Viro Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org --- fs/afs/cell.c | 11 ++++++----- fs/afs/dynroot.c | 15 +++++++++++++-- fs/afs/internal.h | 2 +- fs/afs/proc.c | 4 ++-- 4 files changed, 22 insertions(+), 10 deletions(-) diff --git a/fs/afs/cell.c b/fs/afs/cell.c index cee42646736c..96a6781f3653 100644 --- a/fs/afs/cell.c +++ b/fs/afs/cell.c @@ -64,7 +64,8 @@ static struct afs_cell *afs_find_cell_locked(struct afs_net *net, return ERR_PTR(-ENAMETOOLONG); if (!name) { - cell = net->ws_cell; + cell = rcu_dereference_protected(net->ws_cell, + lockdep_is_held(&net->cells_lock)); if (!cell) return ERR_PTR(-EDESTADDRREQ); goto found; @@ -388,8 +389,8 @@ int afs_cell_init(struct afs_net *net, const char *rootcell) /* install the new cell */ down_write(&net->cells_lock); afs_see_cell(new_root, afs_cell_trace_see_ws); - old_root = net->ws_cell; - net->ws_cell = new_root; + old_root = rcu_replace_pointer(net->ws_cell, new_root, + lockdep_is_held(&net->cells_lock)); up_write(&net->cells_lock); afs_unuse_cell(net, old_root, afs_cell_trace_unuse_ws); @@ -945,8 +946,8 @@ void afs_cell_purge(struct afs_net *net) _enter(""); down_write(&net->cells_lock); - ws = net->ws_cell; - net->ws_cell = NULL; + ws = rcu_replace_pointer(net->ws_cell, NULL, + lockdep_is_held(&net->cells_lock)); up_write(&net->cells_lock); afs_unuse_cell(net, ws, afs_cell_trace_unuse_ws); diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c index d8bf52f77d93..008698d706ca 100644 --- a/fs/afs/dynroot.c +++ b/fs/afs/dynroot.c @@ -314,12 +314,23 @@ static const char *afs_atcell_get_link(struct dentry *dentry, struct inode *inod const char *name; bool dotted = vnode->fid.vnode == 3; - if (!net->ws_cell) + if (!dentry) { + /* We're in RCU-pathwalk. */ + cell = rcu_dereference(net->ws_cell); + if (dotted) + name = cell->name - 1; + else + name = cell->name; + /* Shouldn't need to set a delayed call. */ + return name; + } + + if (!rcu_access_pointer(net->ws_cell)) return ERR_PTR(-ENOENT); down_read(&net->cells_lock); - cell = net->ws_cell; + cell = rcu_dereference_protected(net->ws_cell, lockdep_is_held(&net->cells_lock)); if (dotted) name = cell->name - 1; else diff --git a/fs/afs/internal.h b/fs/afs/internal.h index 90f407774a9a..df30bd62da79 100644 --- a/fs/afs/internal.h +++ b/fs/afs/internal.h @@ -287,7 +287,7 @@ struct afs_net { /* Cell database */ struct rb_root cells; - struct afs_cell *ws_cell; + struct afs_cell __rcu *ws_cell; struct work_struct cells_manager; struct timer_list cells_timer; atomic_t cells_outstanding; diff --git a/fs/afs/proc.c b/fs/afs/proc.c index e7614f4f30c2..12c88d8be3fe 100644 --- a/fs/afs/proc.c +++ b/fs/afs/proc.c @@ -206,7 +206,7 @@ static int afs_proc_rootcell_show(struct seq_file *m, void *v) net = afs_seq2net_single(m); down_read(&net->cells_lock); - cell = net->ws_cell; + cell = rcu_dereference_protected(net->ws_cell, lockdep_is_held(&net->cells_lock)); if (cell) seq_printf(m, "%s\n", cell->name); up_read(&net->cells_lock); @@ -242,7 +242,7 @@ static int afs_proc_rootcell_write(struct file *file, char *buf, size_t size) ret = -EEXIST; inode_lock(file_inode(file)); - if (!net->ws_cell) + if (!rcu_access_pointer(net->ws_cell)) ret = afs_cell_init(net, buf); else printk("busy\n");