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

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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: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff 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
This commit is contained in:
David Howells 2021-11-18 08:58:08 +00:00
parent 80f94f29f6
commit 1bd9c4e4f0
5 changed files with 89 additions and 1 deletions
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1
fs/cachefiles/Makefile
View File

@ -7,6 +7,7 @@ cachefiles-y := \
cache.o \
daemon.o \
main.o \
namei.o \
security.o
cachefiles-$(CONFIG_CACHEFILES_ERROR_INJECTION) += error_inject.o

43
fs/cachefiles/namei.c Normal file
View File

@ -0,0 +1,43 @@
// 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);
}

3
fs/namei.c
View File

@ -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);

1
include/linux/fs.h
View File

@ -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

42
include/trace/events/cachefiles.h
View File

@ -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),