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alistair23-linux/fs/jffs2/acl.c
Andreas Gruenbacher b8a7a3a667 posix_acl: Inode acl caching fixes 
When get_acl() is called for an inode whose ACL is not cached yet, the
get_acl inode operation is called to fetch the ACL from the filesystem.
The inode operation is responsible for updating the cached acl with
set_cached_acl().  This is done without locking at the VFS level, so
another task can call set_cached_acl() or forget_cached_acl() before the
get_acl inode operation gets to calling set_cached_acl(), and then
get_acl's call to set_cached_acl() results in caching an outdate ACL.

Prevent this from happening by setting the cached ACL pointer to a
task-specific sentinel value before calling the get_acl inode operation.
Move the responsibility for updating the cached ACL from the get_acl
inode operations to get_acl().  There, only set the cached ACL if the
sentinel value hasn't changed.

The sentinel values are chosen to have odd values.  Likewise, the value
of ACL_NOT_CACHED is odd.  In contrast, ACL object pointers always have
an even value (ACLs are aligned in memory).  This allows to distinguish
uncached ACLs values from ACL objects.

In addition, switch from guarding inode->i_acl and inode->i_default_acl
upates by the inode->i_lock spinlock to using xchg() and cmpxchg().

Filesystems that do not want ACLs returned from their get_acl inode
operations to be cached must call forget_cached_acl() to prevent the VFS
from doing so.

(Patch written by Al Viro and Andreas Gruenbacher.)

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-03-31 00:30:15 -04:00

308 lines
6.7 KiB
C
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/*
* JFFS2 -- Journalling Flash File System, Version 2.
*
* Copyright © 2006 NEC Corporation
*
* Created by KaiGai Kohei <kaigai@ak.jp.nec.com>
*
* For licensing information, see the file 'LICENCE' in this directory.
*
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/time.h>
#include <linux/crc32.h>
#include <linux/jffs2.h>
#include <linux/xattr.h>
#include <linux/posix_acl_xattr.h>
#include <linux/mtd/mtd.h>
#include "nodelist.h"
static size_t jffs2_acl_size(int count)
{
if (count <= 4) {
return sizeof(struct jffs2_acl_header)
+ count * sizeof(struct jffs2_acl_entry_short);
} else {
return sizeof(struct jffs2_acl_header)
+ 4 * sizeof(struct jffs2_acl_entry_short)
+ (count - 4) * sizeof(struct jffs2_acl_entry);
}
}
static int jffs2_acl_count(size_t size)
{
size_t s;
size -= sizeof(struct jffs2_acl_header);
if (size < 4 * sizeof(struct jffs2_acl_entry_short)) {
if (size % sizeof(struct jffs2_acl_entry_short))
return -1;
return size / sizeof(struct jffs2_acl_entry_short);
} else {
s = size - 4 * sizeof(struct jffs2_acl_entry_short);
if (s % sizeof(struct jffs2_acl_entry))
return -1;
return s / sizeof(struct jffs2_acl_entry) + 4;
}
}
static struct posix_acl *jffs2_acl_from_medium(void *value, size_t size)
{
void *end = value + size;
struct jffs2_acl_header *header = value;
struct jffs2_acl_entry *entry;
struct posix_acl *acl;
uint32_t ver;
int i, count;
if (!value)
return NULL;
if (size < sizeof(struct jffs2_acl_header))
return ERR_PTR(-EINVAL);
ver = je32_to_cpu(header->a_version);
if (ver != JFFS2_ACL_VERSION) {
JFFS2_WARNING("Invalid ACL version. (=%u)\n", ver);
return ERR_PTR(-EINVAL);
}
value += sizeof(struct jffs2_acl_header);
count = jffs2_acl_count(size);
if (count < 0)
return ERR_PTR(-EINVAL);
if (count == 0)
return NULL;
acl = posix_acl_alloc(count, GFP_KERNEL);
if (!acl)
return ERR_PTR(-ENOMEM);
for (i=0; i < count; i++) {
entry = value;
if (value + sizeof(struct jffs2_acl_entry_short) > end)
goto fail;
acl->a_entries[i].e_tag = je16_to_cpu(entry->e_tag);
acl->a_entries[i].e_perm = je16_to_cpu(entry->e_perm);
switch (acl->a_entries[i].e_tag) {
case ACL_USER_OBJ:
case ACL_GROUP_OBJ:
case ACL_MASK:
case ACL_OTHER:
value += sizeof(struct jffs2_acl_entry_short);
break;
case ACL_USER:
value += sizeof(struct jffs2_acl_entry);
if (value > end)
goto fail;
acl->a_entries[i].e_uid =
make_kuid(&init_user_ns,
je32_to_cpu(entry->e_id));
break;
case ACL_GROUP:
value += sizeof(struct jffs2_acl_entry);
if (value > end)
goto fail;
acl->a_entries[i].e_gid =
make_kgid(&init_user_ns,
je32_to_cpu(entry->e_id));
break;
default:
goto fail;
}
}
if (value != end)
goto fail;
return acl;
fail:
posix_acl_release(acl);
return ERR_PTR(-EINVAL);
}
static void *jffs2_acl_to_medium(const struct posix_acl *acl, size_t *size)
{
struct jffs2_acl_header *header;
struct jffs2_acl_entry *entry;
void *e;
size_t i;
*size = jffs2_acl_size(acl->a_count);
header = kmalloc(sizeof(*header) + acl->a_count * sizeof(*entry), GFP_KERNEL);
if (!header)
return ERR_PTR(-ENOMEM);
header->a_version = cpu_to_je32(JFFS2_ACL_VERSION);
e = header + 1;
for (i=0; i < acl->a_count; i++) {
const struct posix_acl_entry *acl_e = &acl->a_entries[i];
entry = e;
entry->e_tag = cpu_to_je16(acl_e->e_tag);
entry->e_perm = cpu_to_je16(acl_e->e_perm);
switch(acl_e->e_tag) {
case ACL_USER:
entry->e_id = cpu_to_je32(
from_kuid(&init_user_ns, acl_e->e_uid));
e += sizeof(struct jffs2_acl_entry);
break;
case ACL_GROUP:
entry->e_id = cpu_to_je32(
from_kgid(&init_user_ns, acl_e->e_gid));
e += sizeof(struct jffs2_acl_entry);
break;
case ACL_USER_OBJ:
case ACL_GROUP_OBJ:
case ACL_MASK:
case ACL_OTHER:
e += sizeof(struct jffs2_acl_entry_short);
break;
default:
goto fail;
}
}
return header;
fail:
kfree(header);
return ERR_PTR(-EINVAL);
}
struct posix_acl *jffs2_get_acl(struct inode *inode, int type)
{
struct posix_acl *acl;
char *value = NULL;
int rc, xprefix;
switch (type) {
case ACL_TYPE_ACCESS:
xprefix = JFFS2_XPREFIX_ACL_ACCESS;
break;
case ACL_TYPE_DEFAULT:
xprefix = JFFS2_XPREFIX_ACL_DEFAULT;
break;
default:
BUG();
}
rc = do_jffs2_getxattr(inode, xprefix, "", NULL, 0);
if (rc > 0) {
value = kmalloc(rc, GFP_KERNEL);
if (!value)
return ERR_PTR(-ENOMEM);
rc = do_jffs2_getxattr(inode, xprefix, "", value, rc);
}
if (rc > 0) {
acl = jffs2_acl_from_medium(value, rc);
} else if (rc == -ENODATA || rc == -ENOSYS) {
acl = NULL;
} else {
acl = ERR_PTR(rc);
}
kfree(value);
return acl;
}
static int __jffs2_set_acl(struct inode *inode, int xprefix, struct posix_acl *acl)
{
char *value = NULL;
size_t size = 0;
int rc;
if (acl) {
value = jffs2_acl_to_medium(acl, &size);
if (IS_ERR(value))
return PTR_ERR(value);
}
rc = do_jffs2_setxattr(inode, xprefix, "", value, size, 0);
if (!value && rc == -ENODATA)
rc = 0;
kfree(value);
return rc;
}
int jffs2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
{
int rc, xprefix;
switch (type) {
case ACL_TYPE_ACCESS:
xprefix = JFFS2_XPREFIX_ACL_ACCESS;
if (acl) {
umode_t mode = inode->i_mode;
rc = posix_acl_equiv_mode(acl, &mode);
if (rc < 0)
return rc;
if (inode->i_mode != mode) {
struct iattr attr;
attr.ia_valid = ATTR_MODE | ATTR_CTIME;
attr.ia_mode = mode;
attr.ia_ctime = CURRENT_TIME_SEC;
rc = jffs2_do_setattr(inode, &attr);
if (rc < 0)
return rc;
}
if (rc == 0)
acl = NULL;
}
break;
case ACL_TYPE_DEFAULT:
xprefix = JFFS2_XPREFIX_ACL_DEFAULT;
if (!S_ISDIR(inode->i_mode))
return acl ? -EACCES : 0;
break;
default:
return -EINVAL;
}
rc = __jffs2_set_acl(inode, xprefix, acl);
if (!rc)
set_cached_acl(inode, type, acl);
return rc;
}
int jffs2_init_acl_pre(struct inode *dir_i, struct inode *inode, umode_t *i_mode)
{
struct posix_acl *default_acl, *acl;
int rc;
cache_no_acl(inode);
rc = posix_acl_create(dir_i, i_mode, &default_acl, &acl);
if (rc)
return rc;
if (default_acl) {
set_cached_acl(inode, ACL_TYPE_DEFAULT, default_acl);
posix_acl_release(default_acl);
}
if (acl) {
set_cached_acl(inode, ACL_TYPE_ACCESS, acl);
posix_acl_release(acl);
}
return 0;
}
int jffs2_init_acl_post(struct inode *inode)
{
int rc;
if (inode->i_default_acl) {
rc = __jffs2_set_acl(inode, JFFS2_XPREFIX_ACL_DEFAULT, inode->i_default_acl);
if (rc)
return rc;
}
if (inode->i_acl) {
rc = __jffs2_set_acl(inode, JFFS2_XPREFIX_ACL_ACCESS, inode->i_acl);
if (rc)
return rc;
}
return 0;
}
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