1 files changed, 110 insertions, 5 deletions

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 00530e82673..8ee9dc2f9e4 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -27,6 +27,13 @@
 #define DEVPTS_SUPER_MAGIC 0x1cd1
 
 #define DEVPTS_DEFAULT_MODE 0600
+/*
+ * ptmx is a new node in /dev/pts and will be unused in legacy (single-
+ * instance) mode. To prevent surprises in user space, set permissions of
+ * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
+ * permissions.
+ */
+#define DEVPTS_DEFAULT_PTMX_MODE 0000
 #define PTMX_MINOR      2
 
 extern int pty_limit;                   /* Config limit on Unix98 ptys */
@@ -40,10 +47,11 @@ struct pts_mount_opts {
         uid_t   uid;
         gid_t   gid;
         umode_t mode;
+        umode_t ptmxmode;
 };
 
 enum {
-        Opt_uid, Opt_gid, Opt_mode,
+        Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode,
         Opt_err
 };
 
@@ -51,12 +59,16 @@ static const match_table_t tokens = {
         {Opt_uid, "uid=%u"},
         {Opt_gid, "gid=%u"},
         {Opt_mode, "mode=%o"},
+#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
+        {Opt_ptmxmode, "ptmxmode=%o"},
+#endif
         {Opt_err, NULL}
 };
 
 struct pts_fs_info {
         struct ida allocated_ptys;
         struct pts_mount_opts mount_opts;
+        struct dentry *ptmx_dentry;
 };
 
 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
@@ -81,6 +93,7 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
         opts->uid     = 0;
         opts->gid     = 0;
         opts->mode    = DEVPTS_DEFAULT_MODE;
+        opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 
         while ((p = strsep(&data, ",")) != NULL) {
                 substring_t args[MAX_OPT_ARGS];
@@ -109,6 +122,13 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
                                 return -EINVAL;
                         opts->mode = option & S_IALLUGO;
                         break;
+#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
+                case Opt_ptmxmode:
+                        if (match_octal(&args[0], &option))
+                                return -EINVAL;
+                        opts->ptmxmode = option & S_IALLUGO;
+                        break;
+#endif
                 default:
                         printk(KERN_ERR "devpts: called with bogus options\n");
                         return -EINVAL;
@@ -118,12 +138,93 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
         return 0;
 }
 
+#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
+static int mknod_ptmx(struct super_block *sb)
+{
+        int mode;
+        int rc = -ENOMEM;
+        struct dentry *dentry;
+        struct inode *inode;
+        struct dentry *root = sb->s_root;
+        struct pts_fs_info *fsi = DEVPTS_SB(sb);
+        struct pts_mount_opts *opts = &fsi->mount_opts;
+
+        mutex_lock(&root->d_inode->i_mutex);
+
+        /* If we have already created ptmx node, return */
+        if (fsi->ptmx_dentry) {
+                rc = 0;
+                goto out;
+        }
+
+        dentry = d_alloc_name(root, "ptmx");
+        if (!dentry) {
+                printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
+                goto out;
+        }
+
+        /*
+         * Create a new 'ptmx' node in this mount of devpts.
+         */
+        inode = new_inode(sb);
+        if (!inode) {
+                printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
+                dput(dentry);
+                goto out;
+        }
+
+        inode->i_ino = 2;
+        inode->i_uid = inode->i_gid = 0;
+        inode->i_blocks = 0;
+        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+
+        mode = S_IFCHR|opts->ptmxmode;
+        init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
+
+        d_add(dentry, inode);
+
+        fsi->ptmx_dentry = dentry;
+        rc = 0;
+
+        printk(KERN_DEBUG "Created ptmx node in devpts ino %lu\n",
+                        inode->i_ino);
+out:
+        mutex_unlock(&root->d_inode->i_mutex);
+        return rc;
+}
+
+static void update_ptmx_mode(struct pts_fs_info *fsi)
+{
+        struct inode *inode;
+        if (fsi->ptmx_dentry) {
+                inode = fsi->ptmx_dentry->d_inode;
+                inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
+        }
+}
+#else
+static inline void update_ptmx_mode(struct pts_fs_info *fsi)
+{
+       return;
+}
+#endif
+
 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 {
+        int err;
         struct pts_fs_info *fsi = DEVPTS_SB(sb);
         struct pts_mount_opts *opts = &fsi->mount_opts;
 
-        return parse_mount_options(data, opts);
+        err = parse_mount_options(data, opts);
+
+        /*
+         * parse_mount_options() restores options to default values
+         * before parsing and may have changed ptmxmode. So, update the
+         * mode in the inode too. Bogus options don't fail the remount,
+         * so do this even on error return.
+         */
+        update_ptmx_mode(fsi);
+
+        return err;
 }
 
 static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
@@ -136,6 +237,9 @@ static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
         if (opts->setgid)
                 seq_printf(seq, ",gid=%u", opts->gid);
         seq_printf(seq, ",mode=%03o", opts->mode);
+#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
+        seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
+#endif
 
         return 0;
 }
@@ -156,6 +260,7 @@ static void *new_pts_fs_info(void)
 
         ida_init(&fsi->allocated_ptys);
         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
+        fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 
         return fsi;
 }
@@ -163,7 +268,7 @@ static void *new_pts_fs_info(void)
 static int
 devpts_fill_super(struct super_block *s, void *data, int silent)
 {
-        struct inode * inode;
+        struct inode *inode;
 
         s->s_blocksize = 1024;
         s->s_blocksize_bits = 10;
@@ -190,7 +295,7 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
         s->s_root = d_alloc_root(inode);
         if (s->s_root)
                 return 0;
-        
+
         printk("devpts: get root dentry failed\n");
         iput(inode);
 
@@ -211,7 +316,7 @@ static void devpts_kill_sb(struct super_block *sb)
         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 
         kfree(fsi);
-        kill_anon_super(sb);
+        kill_litter_super(sb);
 }
 
 static struct file_system_type devpts_fs_type = {