From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 CA00353CA85 for ; Wed, 16 Sep 2026 14:42:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789569741; cv=none; b=J2NMstLrolbfl/9TBQAgZwanTCRJXNj4xEF1joNcwRAxAdCIJNZt/d1AHwMJuxK4vuqC2gQFajjWCbOPdDGVP4LjzTPGgOBAQ0hMuNErVlRVUEu5SAayw4pHuobPBczATCUG6TH/qS9hUXLYyQ9WLON0cksOzIWBjt9HD6TLAng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789569741; c=relaxed/simple; bh=0j9LmuSz/S7KLGjPVlrvtHmlAHuUvgo6r5kx5NWWg8o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ecPOgzRWG5h+4i5XsjkzD7WOKBsk9E0H1PJyHu9Ff1mR82SIzXx0D8+mpIwcKzSv1+3WzHj6PMjvXT2vmnK4Y1EiPA+IzzRZUHkPtt5kRrg8f3COA2XnST9bOi6ej2zDMFNh8INDjmvgP7w/ksMPhKK40Hm5S1n92/SzoCsYYNo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MLSHB8H3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MLSHB8H3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3A811F0089A; Wed, 16 Sep 2026 14:42:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789569739; bh=P1BD/TRayNCwNCx3mEnQNNldmydQjvNYjTXB88/AVMk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MLSHB8H3V0VuOBmFTEC5uapRkfltHBk+rHMVgiHDDgnXU+dVaBXQ7byRLjme6884p sb27RBxCfMqyAUagzOrYxF7hrjsU6IRvA0kElVYjSxX5S3UV3mJpGfcPdgNou6Ptrn ws5+ibHBH+WGe82xCOIQ+IxIG/DEIfP887gcfbmJTHQddk1JnSTlrzTNCJ2pgN7uih +xSQ2jYK9nWqGi9Rykgv3I6nTYt61W3XwkokK8xLTVR1boEy/tv6F0j8X7vcSQmQL0 MbvbCZKj+PXx3m7VBVHOn0ebUquoVTMhGC8lK+CDpD13kIoAlrnvhiZikZ809lNz4p VPKJOMH/gy8rA== From: Sasha Levin To: stable@vger.kernel.org Cc: Vasileios Almpanis , Breno Leitao , Sasha Levin Subject: [PATCH 6.1.y 3/3] configfs: pin the symlink target's dirent instead of chasing ->ci_dentry Date: Wed, 16 Sep 2026 10:42:15 -0400 Message-ID: <20260916144215.3565253-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260916144215.3565253-1-sashal@kernel.org> References: <2026091643-quickness-ammonia-8ff3@gregkh> <20260916144215.3565253-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Vasileios Almpanis [ Upstream commit a7c1290eef60711c10289c056ad32ed1f2b47b12 ] create_link() reads the target's configfs_dirent from item->ci_dentry->d_fsdata, relying on the item reference taken by get_target(). That reference pins the item, not its dentry: the dentry is pinned by DCACHE_PERSISTENT, which configfs_remove_dir() releases via simple_rmdir() while the item is still alive. A symlink racing with rmdir of its target can therefore find ->ci_dentry freed and its dirent released, triggering WARN_ON(!atomic_read(&sd->s_count)) in configfs_get(). Take the dirent in get_target() as well, under ->d_lock and atomically with the item reference, and pass it down to create_link(). A hashed dentry has not been killed yet, so its ->d_fsdata reference keeps the dirent alive there. Cc: stable@vger.kernel.org Fixes: 7063fbf22611 ("[PATCH] configfs: User-driven configuration filesystem") Signed-off-by: Vasileios Almpanis Tested-by: Breno Leitao Reviewed-by: Breno Leitao Link: https://patch.msgid.link/20260730093435.195441-2-vasilisalmpanis@gmail.com Signed-off-by: Breno Leitao Signed-off-by: Sasha Levin --- fs/configfs/symlink.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c index 31b3a4ad5ea66..feaccac55d8cd 100644 --- a/fs/configfs/symlink.c +++ b/fs/configfs/symlink.c @@ -76,9 +76,9 @@ static int configfs_get_target_path(struct config_item *item, static int create_link(struct config_item *parent_item, struct config_item *item, + struct configfs_dirent *target_sd, struct dentry *dentry) { - struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata; char *body; int ret; @@ -115,6 +115,7 @@ static int create_link(struct config_item *parent_item, static int get_target(const char *symname, struct config_item **target, + struct configfs_dirent **target_sd, struct super_block *sb) { struct path path __free(path_put) = {}; @@ -125,7 +126,20 @@ static int get_target(const char *symname, struct config_item **target, return ret; if (path.dentry->d_sb != sb) return -EPERM; - *target = configfs_get_config_item(path.dentry); + /* + * A hashed dentry guarantees that neither the item nor the dirent + * have been released yet, as removals unhash before dropping. + * Grab both references here. An item reference alone would not keep + * ->ci_dentry alive. + */ + spin_lock(&path.dentry->d_lock); + if (!d_unhashed(path.dentry)) { + struct configfs_dirent *sd = path.dentry->d_fsdata; + + *target = config_item_get(sd->s_element); + *target_sd = configfs_get(sd); + } + spin_unlock(&path.dentry->d_lock); if (!*target) return -ENOENT; return 0; @@ -139,6 +153,7 @@ int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir, struct configfs_dirent *sd; struct config_item *parent_item; struct config_item *target_item = NULL; + struct configfs_dirent *target_sd = NULL; const struct config_item_type *type; sd = dentry->d_parent->d_fsdata; @@ -182,7 +197,7 @@ int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir, * AV, a thoroughly annoyed bastard. */ inode_unlock(dir); - ret = get_target(symname, &target_item, dentry->d_sb); + ret = get_target(symname, &target_item, &target_sd, dentry->d_sb); inode_lock(dir); if (ret) goto out_put; @@ -196,13 +211,14 @@ int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir, ret = type->ct_item_ops->allow_link(parent_item, target_item); if (!ret) { mutex_lock(&configfs_symlink_mutex); - ret = create_link(parent_item, target_item, dentry); + ret = create_link(parent_item, target_item, target_sd, dentry); mutex_unlock(&configfs_symlink_mutex); if (ret && type->ct_item_ops->drop_link) type->ct_item_ops->drop_link(parent_item, target_item); } + configfs_put(target_sd); config_item_put(target_item); out_put: -- 2.53.0