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proc: Allow creating permanently empty directories that serve as mount points

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Add a new function proc_create_mount_point that when used to creates a
directory that can not be added to.

Add a new function is_empty_pde to test if a function is a mount
point.

Update the code to use make_empty_dir_inode when reporting
a permanently empty directory to the vfs.

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

Update /proc/openprom and /proc/fs/nfsd to be permanently empty directories.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2015-05-11 16:44:25 -05:00
parent f9bd6733d3
commit eb6d38d542
4 changed files with 35 additions and 2 deletions
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23
fs/proc/generic.c
View file

@ -373,6 +373,10 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
WARN(1, "create '/proc/%s' by hand\n", qstr.name);
return NULL;
}
if (is_empty_pde(*parent)) {
WARN(1, "attempt to add to permanently empty directory");
return NULL;
}
ent = kzalloc(sizeof(struct proc_dir_entry) + qstr.len + 1, GFP_KERNEL);
if (!ent)
@ -455,6 +459,25 @@ struct proc_dir_entry *proc_mkdir(const char *name,
}
EXPORT_SYMBOL(proc_mkdir);
struct proc_dir_entry *proc_create_mount_point(const char *name)
{
umode_t mode = S_IFDIR | S_IRUGO | S_IXUGO;
struct proc_dir_entry *ent, *parent = NULL;
ent = __proc_create(&parent, name, mode, 2);
if (ent) {
ent->data = NULL;
ent->proc_fops = NULL;
ent->proc_iops = NULL;
if (proc_register(parent, ent) < 0) {
kfree(ent);
parent->nlink--;
ent = NULL;
}
}
return ent;
}
struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
struct proc_dir_entry *parent,
const struct file_operations *proc_fops,

4
fs/proc/inode.c
View file

@ -423,6 +423,10 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
PROC_I(inode)->pde = de;
if (is_empty_pde(de)) {
make_empty_dir_inode(inode);
return inode;
}
if (de->mode) {
inode->i_mode = de->mode;
inode->i_uid = de->uid;

6
fs/proc/internal.h
View file

@ -191,6 +191,12 @@ static inline struct proc_dir_entry *pde_get(struct proc_dir_entry *pde)
}
extern void pde_put(struct proc_dir_entry *);
static inline bool is_empty_pde(const struct proc_dir_entry *pde)
{
return S_ISDIR(pde->mode) && !pde->proc_iops;
}
struct proc_dir_entry *proc_create_mount_point(const char *name);
/*
* inode.c
*/

4
fs/proc/root.c
View file

@ -179,10 +179,10 @@ void __init proc_root_init(void)
#endif
proc_mkdir("fs", NULL);
proc_mkdir("driver", NULL);
proc_mkdir("fs/nfsd", NULL); /* somewhere for the nfsd filesystem to be mounted */
proc_create_mount_point("fs/nfsd"); /* somewhere for the nfsd filesystem to be mounted */
#if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
/* just give it a mountpoint */
proc_mkdir("openprom", NULL);
proc_create_mount_point("openprom");
#endif
proc_tty_init();
proc_mkdir("bus", NULL);