From:   Amir Goldstein <amir73il@gmail.com>
To:     Jan Kara <jack@suse.cz>
Cc:     Matthew Bobrowski <repnop@google.com>,
        Ivan Delalande <colona@arista.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org
Subject: [PATCH v2 2/2] fsnotify: fix fsnotify hooks in pseudo filesystems
Date:   Thu, 20 Jan 2022 23:53:05 +0200
Message-Id: <20220120215305.282577-2-amir73il@gmail.com>
In-Reply-To: <20220120215305.282577-1-amir73il@gmail.com>
References: <20220120215305.282577-1-amir73il@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Commit 49246466a989 ("fsnotify: move fsnotify_nameremove() hook out of
d_delete()") moved the fsnotify delete hook before d_delete() so fsnotify
will have access to a positive dentry.

This allowed a race where opening the deleted file via cached dentry
is now possible after receiving the IN_DELETE event.

To fix the regression in pseudo filesystems, convert d_delete() calls
to d_drop() (see commit 46c46f8df9aa ("devpts_pty_kill(): don't bother
with d_delete()") and move the fsnotify hook after d_drop().

Add a missing fsnotify_unlink() hook in nfsdfs that was found during
the audit of fsnotify hooks in pseudo filesystems.

Note that the fsnotify hooks in simple_recursive_removal() follow
d_invalidate(), so they require no change.

Reported-by: Ivan Delalande <colona@arista.com>
Link: https://lore.kernel.org/linux-fsdevel/YeNyzoDM5hP5LtGW@visor/
Fixes: 49246466a989 ("fsnotify: move fsnotify_nameremove() hook out of d_delete()")
Cc: stable@vger.kernel.org # v5.3+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/configfs/dir.c     | 6 +++---
 fs/devpts/inode.c     | 2 +-
 fs/nfsd/nfsctl.c      | 5 +++--
 net/sunrpc/rpc_pipe.c | 4 ++--
 4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 1466b5d01cbb..d3cd2a94d1e8 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1780,8 +1780,8 @@ void configfs_unregister_group(struct config_group *group)
 	configfs_detach_group(&group->cg_item);
 	d_inode(dentry)->i_flags |= S_DEAD;
 	dont_mount(dentry);
+	d_drop(dentry);
 	fsnotify_rmdir(d_inode(parent), dentry);
-	d_delete(dentry);
 	inode_unlock(d_inode(parent));
 
 	dput(dentry);
@@ -1922,10 +1922,10 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
 	configfs_detach_group(&group->cg_item);
 	d_inode(dentry)->i_flags |= S_DEAD;
 	dont_mount(dentry);
-	fsnotify_rmdir(d_inode(root), dentry);
 	inode_unlock(d_inode(dentry));
 
-	d_delete(dentry);
+	d_drop(dentry);
+	fsnotify_rmdir(d_inode(root), dentry);
 
 	inode_unlock(d_inode(root));
 
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 42e5a766d33c..4f25015aa534 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -621,8 +621,8 @@ void devpts_pty_kill(struct dentry *dentry)
 
 	dentry->d_fsdata = NULL;
 	drop_nlink(dentry->d_inode);
-	fsnotify_unlink(d_inode(dentry->d_parent), dentry);
 	d_drop(dentry);
+	fsnotify_unlink(d_inode(dentry->d_parent), dentry);
 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
 }
 
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 51a49e0cfe37..d0761ca8cb54 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1249,7 +1249,8 @@ static void nfsdfs_remove_file(struct inode *dir, struct dentry *dentry)
 	clear_ncl(d_inode(dentry));
 	dget(dentry);
 	ret = simple_unlink(dir, dentry);
-	d_delete(dentry);
+	d_drop(dentry);
+	fsnotify_unlink(dir, dentry);
 	dput(dentry);
 	WARN_ON_ONCE(ret);
 }
@@ -1340,8 +1341,8 @@ void nfsd_client_rmdir(struct dentry *dentry)
 	dget(dentry);
 	ret = simple_rmdir(dir, dentry);
 	WARN_ON_ONCE(ret);
+	d_drop(dentry);
 	fsnotify_rmdir(dir, dentry);
-	d_delete(dentry);
 	dput(dentry);
 	inode_unlock(dir);
 }
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index ee5336d73fdd..35588f0afa86 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -600,9 +600,9 @@ static int __rpc_rmdir(struct inode *dir, struct dentry *dentry)
 
 	dget(dentry);
 	ret = simple_rmdir(dir, dentry);
+	d_drop(dentry);
 	if (!ret)
 		fsnotify_rmdir(dir, dentry);
-	d_delete(dentry);
 	dput(dentry);
 	return ret;
 }
@@ -613,9 +613,9 @@ static int __rpc_unlink(struct inode *dir, struct dentry *dentry)
 
 	dget(dentry);
 	ret = simple_unlink(dir, dentry);
+	d_drop(dentry);
 	if (!ret)
 		fsnotify_unlink(dir, dentry);
-	d_delete(dentry);
 	dput(dentry);
 	return ret;
 }
-- 
2.34.1