[PATCH] VFS: Permit filesystem to override root dentry on mount
[linux-2.6.git] / fs / devpts / inode.c
1 /* -*- linux-c -*- --------------------------------------------------------- *
2  *
3  * linux/fs/devpts/inode.c
4  *
5  *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
6  *
7  * This file is part of the Linux kernel and is made available under
8  * the terms of the GNU General Public License, version 2, or at your
9  * option, any later version, incorporated herein by reference.
10  *
11  * ------------------------------------------------------------------------- */
12
13 #include <linux/module.h>
14 #include <linux/init.h>
15 #include <linux/fs.h>
16 #include <linux/sched.h>
17 #include <linux/namei.h>
18 #include <linux/mount.h>
19 #include <linux/tty.h>
20 #include <linux/devpts_fs.h>
21 #include <linux/parser.h>
22
23 #define DEVPTS_SUPER_MAGIC 0x1cd1
24
25 static struct vfsmount *devpts_mnt;
26 static struct dentry *devpts_root;
27
28 static struct {
29         int setuid;
30         int setgid;
31         uid_t   uid;
32         gid_t   gid;
33         umode_t mode;
34 } config = {.mode = 0600};
35
36 enum {
37         Opt_uid, Opt_gid, Opt_mode,
38         Opt_err
39 };
40
41 static match_table_t tokens = {
42         {Opt_uid, "uid=%u"},
43         {Opt_gid, "gid=%u"},
44         {Opt_mode, "mode=%o"},
45         {Opt_err, NULL}
46 };
47
48 static int devpts_remount(struct super_block *sb, int *flags, char *data)
49 {
50         char *p;
51
52         config.setuid  = 0;
53         config.setgid  = 0;
54         config.uid     = 0;
55         config.gid     = 0;
56         config.mode    = 0600;
57
58         while ((p = strsep(&data, ",")) != NULL) {
59                 substring_t args[MAX_OPT_ARGS];
60                 int token;
61                 int option;
62
63                 if (!*p)
64                         continue;
65
66                 token = match_token(p, tokens, args);
67                 switch (token) {
68                 case Opt_uid:
69                         if (match_int(&args[0], &option))
70                                 return -EINVAL;
71                         config.uid = option;
72                         config.setuid = 1;
73                         break;
74                 case Opt_gid:
75                         if (match_int(&args[0], &option))
76                                 return -EINVAL;
77                         config.gid = option;
78                         config.setgid = 1;
79                         break;
80                 case Opt_mode:
81                         if (match_octal(&args[0], &option))
82                                 return -EINVAL;
83                         config.mode = option & ~S_IFMT;
84                         break;
85                 default:
86                         printk(KERN_ERR "devpts: called with bogus options\n");
87                         return -EINVAL;
88                 }
89         }
90
91         return 0;
92 }
93
94 static struct super_operations devpts_sops = {
95         .statfs         = simple_statfs,
96         .remount_fs     = devpts_remount,
97 };
98
99 static int
100 devpts_fill_super(struct super_block *s, void *data, int silent)
101 {
102         struct inode * inode;
103
104         s->s_blocksize = 1024;
105         s->s_blocksize_bits = 10;
106         s->s_magic = DEVPTS_SUPER_MAGIC;
107         s->s_op = &devpts_sops;
108         s->s_time_gran = 1;
109
110         inode = new_inode(s);
111         if (!inode)
112                 goto fail;
113         inode->i_ino = 1;
114         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
115         inode->i_blocks = 0;
116         inode->i_blksize = 1024;
117         inode->i_uid = inode->i_gid = 0;
118         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
119         inode->i_op = &simple_dir_inode_operations;
120         inode->i_fop = &simple_dir_operations;
121         inode->i_nlink = 2;
122
123         devpts_root = s->s_root = d_alloc_root(inode);
124         if (s->s_root)
125                 return 0;
126         
127         printk("devpts: get root dentry failed\n");
128         iput(inode);
129 fail:
130         return -ENOMEM;
131 }
132
133 static int devpts_get_sb(struct file_system_type *fs_type,
134         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
135 {
136         return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
137 }
138
139 static struct file_system_type devpts_fs_type = {
140         .owner          = THIS_MODULE,
141         .name           = "devpts",
142         .get_sb         = devpts_get_sb,
143         .kill_sb        = kill_anon_super,
144 };
145
146 /*
147  * The normal naming convention is simply /dev/pts/<number>; this conforms
148  * to the System V naming convention
149  */
150
151 static struct dentry *get_node(int num)
152 {
153         char s[12];
154         struct dentry *root = devpts_root;
155         mutex_lock(&root->d_inode->i_mutex);
156         return lookup_one_len(s, root, sprintf(s, "%d", num));
157 }
158
159 int devpts_pty_new(struct tty_struct *tty)
160 {
161         int number = tty->index;
162         struct tty_driver *driver = tty->driver;
163         dev_t device = MKDEV(driver->major, driver->minor_start+number);
164         struct dentry *dentry;
165         struct inode *inode = new_inode(devpts_mnt->mnt_sb);
166
167         /* We're supposed to be given the slave end of a pty */
168         BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
169         BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
170
171         if (!inode)
172                 return -ENOMEM;
173
174         inode->i_ino = number+2;
175         inode->i_blksize = 1024;
176         inode->i_uid = config.setuid ? config.uid : current->fsuid;
177         inode->i_gid = config.setgid ? config.gid : current->fsgid;
178         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
179         init_special_inode(inode, S_IFCHR|config.mode, device);
180         inode->u.generic_ip = tty;
181
182         dentry = get_node(number);
183         if (!IS_ERR(dentry) && !dentry->d_inode)
184                 d_instantiate(dentry, inode);
185
186         mutex_unlock(&devpts_root->d_inode->i_mutex);
187
188         return 0;
189 }
190
191 struct tty_struct *devpts_get_tty(int number)
192 {
193         struct dentry *dentry = get_node(number);
194         struct tty_struct *tty;
195
196         tty = NULL;
197         if (!IS_ERR(dentry)) {
198                 if (dentry->d_inode)
199                         tty = dentry->d_inode->u.generic_ip;
200                 dput(dentry);
201         }
202
203         mutex_unlock(&devpts_root->d_inode->i_mutex);
204
205         return tty;
206 }
207
208 void devpts_pty_kill(int number)
209 {
210         struct dentry *dentry = get_node(number);
211
212         if (!IS_ERR(dentry)) {
213                 struct inode *inode = dentry->d_inode;
214                 if (inode) {
215                         inode->i_nlink--;
216                         d_delete(dentry);
217                         dput(dentry);
218                 }
219                 dput(dentry);
220         }
221         mutex_unlock(&devpts_root->d_inode->i_mutex);
222 }
223
224 static int __init init_devpts_fs(void)
225 {
226         int err = register_filesystem(&devpts_fs_type);
227         if (!err) {
228                 devpts_mnt = kern_mount(&devpts_fs_type);
229                 if (IS_ERR(devpts_mnt))
230                         err = PTR_ERR(devpts_mnt);
231         }
232         return err;
233 }
234
235 static void __exit exit_devpts_fs(void)
236 {
237         unregister_filesystem(&devpts_fs_type);
238         mntput(devpts_mnt);
239 }
240
241 module_init(init_devpts_fs)
242 module_exit(exit_devpts_fs)
243 MODULE_LICENSE("GPL");