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sysctl: Allow creating permanently empty directories that serve as mountpoints. 

Add a magic sysctl table sysctl_mount_point that when used to
create a directory forces that directory to be permanently empty.

Update the code to use make_empty_dir_inode when accessing permanently
empty directories.

Update the code to not allow adding to permanently empty directories.

Update /proc/sys/fs/binfmt_misc to be a permanently empty directory.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
hifive-unleashed-5.1
Eric W. Biederman 2015-05-09 22:09:14 -05:00
parent fbabfd0f4e
commit f9bd6733d3
3 changed files with 41 additions and 7 deletions
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37
fs/proc/proc_sysctl.c
View File

@ -19,6 +19,28 @@ static const struct inode_operations proc_sys_inode_operations;
static const struct file_operations proc_sys_dir_file_operations;
static const struct inode_operations proc_sys_dir_operations;
/* Support for permanently empty directories */
struct ctl_table sysctl_mount_point[] = {
{ }
};
static bool is_empty_dir(struct ctl_table_header *head)
{
return head->ctl_table[0].child == sysctl_mount_point;
}
static void set_empty_dir(struct ctl_dir *dir)
{
dir->header.ctl_table[0].child = sysctl_mount_point;
}
static void clear_empty_dir(struct ctl_dir *dir)
{
dir->header.ctl_table[0].child = NULL;
}
void proc_sys_poll_notify(struct ctl_table_poll *poll)
{
if (!poll)
@ -187,6 +209,17 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
struct ctl_table *entry;
int err;
/* Is this a permanently empty directory? */
if (is_empty_dir(&dir->header))
return -EROFS;
/* Am I creating a permanently empty directory? */
if (header->ctl_table == sysctl_mount_point) {
if (!RB_EMPTY_ROOT(&dir->root))
return -EINVAL;
set_empty_dir(dir);
}
dir->header.nreg++;
header->parent = dir;
err = insert_links(header);
@ -202,6 +235,8 @@ fail:
erase_header(header);
put_links(header);
fail_links:
if (header->ctl_table == sysctl_mount_point)
clear_empty_dir(dir);
header->parent = NULL;
drop_sysctl_table(&dir->header);
return err;
@ -419,6 +454,8 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
inode->i_mode |= S_IFDIR;
inode->i_op = &proc_sys_dir_operations;
inode->i_fop = &proc_sys_dir_file_operations;
if (is_empty_dir(head))
make_empty_dir_inode(inode);
}
out:
return inode;

3
include/linux/sysctl.h
View File

@ -188,6 +188,9 @@ struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
void unregister_sysctl_table(struct ctl_table_header * table);
extern int sysctl_init(void);
extern struct ctl_table sysctl_mount_point[];
#else /* CONFIG_SYSCTL */
static inline struct ctl_table_header *register_sysctl_table(struct ctl_table * table)
{

8
kernel/sysctl.c
View File

@ -1531,12 +1531,6 @@ static struct ctl_table vm_table[] = {
{ }
};
#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
static struct ctl_table binfmt_misc_table[] = {
{ }
};
#endif
static struct ctl_table fs_table[] = {
{
.procname = "inode-nr",
@ -1690,7 +1684,7 @@ static struct ctl_table fs_table[] = {
{
.procname = "binfmt_misc",
.mode = 0555,
.child = binfmt_misc_table,
.child = sysctl_mount_point,
},
#endif
{