Commit 1bd9c4e4 authored by David Howells's avatar David Howells
Browse files

vfs, cachefiles: Mark a backing file in use with an inode flag 



Use an inode flag, S_KERNEL_FILE, to mark that a backing file is in use by
the kernel to prevent cachefiles or other kernel services from interfering
with that file.

Alter rmdir to reject attempts to remove a directory marked with this flag.
This is used by cachefiles to prevent cachefilesd from removing them.

Using S_SWAPFILE instead isn't really viable as that has other effects in
the I/O paths.

Changes
=======
ver #3:
 - Check for the object pointer being NULL in the tracepoints rather than
   the caller.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819630256.215744.4815885535039369574.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906931596.143852.8642051223094013028.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967141000.1823006.12920680657559677789.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021541207.640689.564689725898537127.stgit@warthog.procyon.org.uk/ # v4
parent 80f94f29

fs/cachefiles/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ cachefiles-y := \ 
	cache.o \

	daemon.o \

	main.o \

	namei.o \

	security.o



cachefiles-$(CONFIG_CACHEFILES_ERROR_INJECTION) += error_inject.o

fs/cachefiles/namei.c

0 → 100644
+43 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-or-later

/* CacheFiles path walking and related routines

 *

 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.

 * Written by David Howells (dhowells@redhat.com)

 */



#include <linux/fs.h>

#include "internal.h"



/*

 * Mark the backing file as being a cache file if it's not already in use.  The

 * mark tells the culling request command that it's not allowed to cull the

 * file or directory.  The caller must hold the inode lock.

 */

static bool __cachefiles_mark_inode_in_use(struct cachefiles_object *object,

					   struct dentry *dentry)

{

	struct inode *inode = d_backing_inode(dentry);

	bool can_use = false;



	if (!(inode->i_flags & S_KERNEL_FILE)) {

		inode->i_flags |= S_KERNEL_FILE;

		trace_cachefiles_mark_active(object, inode);

		can_use = true;

	} else {

		pr_notice("cachefiles: Inode already in use: %pd\n", dentry);

	}



	return can_use;

}



/*

 * Unmark a backing inode.  The caller must hold the inode lock.

 */

static void __cachefiles_unmark_inode_in_use(struct cachefiles_object *object,

					     struct dentry *dentry)

{

	struct inode *inode = d_backing_inode(dentry);



	inode->i_flags &= ~S_KERNEL_FILE;

	trace_cachefiles_mark_inactive(object, inode);

}

fs/namei.c

+2 −1
Original line number Diff line number Diff line
@@ -3958,7 +3958,8 @@ int vfs_rmdir(struct user_namespace *mnt_userns, struct inode *dir, 
	inode_lock(dentry->d_inode);



	error = -EBUSY;

	if (is_local_mountpoint(dentry))

	if (is_local_mountpoint(dentry) ||

	    (dentry->d_inode->i_flags & S_KERNEL_FILE))

		goto out;



	error = security_inode_rmdir(dir, dentry);

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -2249,6 +2249,7 @@ struct super_operations { 
#define S_ENCRYPTED	(1 << 14) /* Encrypted file (using fs/crypto/) */

#define S_CASEFOLD	(1 << 15) /* Casefolded file */

#define S_VERITY	(1 << 16) /* Verity file (using fs/verity/) */

#define S_KERNEL_FILE	(1 << 17) /* File is in use by the kernel (eg. fs/cachefiles) */



/*

 * Note that nosuid etc flags are inode-specific: setting some file-system

include/trace/events/cachefiles.h

+42 −0
Original line number Diff line number Diff line
@@ -83,6 +83,48 @@ cachefiles_error_traces; 
#define E_(a, b)	{ a, b }





TRACE_EVENT(cachefiles_mark_active,

	    TP_PROTO(struct cachefiles_object *obj,

		     struct inode *inode),



	    TP_ARGS(obj, inode),



	    /* Note that obj may be NULL */

	    TP_STRUCT__entry(

		    __field(unsigned int,		obj		)

		    __field(ino_t,			inode		)

			     ),



	    TP_fast_assign(

		    __entry->obj	= obj ? obj->debug_id : 0;

		    __entry->inode	= inode->i_ino;

			   ),



	    TP_printk("o=%08x i=%lx",

		      __entry->obj, __entry->inode)

	    );



TRACE_EVENT(cachefiles_mark_inactive,

	    TP_PROTO(struct cachefiles_object *obj,

		     struct inode *inode),



	    TP_ARGS(obj, inode),



	    /* Note that obj may be NULL */

	    TP_STRUCT__entry(

		    __field(unsigned int,		obj		)

		    __field(ino_t,			inode		)

			     ),



	    TP_fast_assign(

		    __entry->obj	= obj ? obj->debug_id : 0;

		    __entry->inode	= inode->i_ino;

			   ),



	    TP_printk("o=%08x i=%lx",

		      __entry->obj, __entry->inode)

	    );



TRACE_EVENT(cachefiles_vfs_error,

	    TP_PROTO(struct cachefiles_object *obj, struct inode *backer,

		     int error, enum cachefiles_error_trace where),