From 1f8f1e296583f9f832c2fe7b5a219675b74bf43e Mon Sep 17 00:00:00 2001 From: Sukadev Bhattiprolu Date: Fri, 2 Jan 2009 13:42:02 +0000 Subject: [PATCH] Define mknod_ptmx() /dev/ptmx is closely tied to the devpts filesystem. An open of /dev/ptmx, allocates the next pty index and the associated device shows up in the devpts fs as /dev/pts/n. Wih multiple instancs of devpts filesystem, during an open of /dev/ptmx we would be unable to determine which instance of the devpts is being accessed. So we move the 'ptmx' node into /dev/pts and use the inode of the 'ptmx' node to identify the superblock and hence the devpts instance. This patch adds ability for the kernel to internally create the [ptmx, c, 5:2] device when mounting devpts filesystem. Since the ptmx node in devpts is new and may surprise some userspace scripts, the default permissions for the new node is 0000. These permissions can be changed either using chmod or by remounting with the new '-o ptmxmode=0666' mount option. Changelog[v5]: - [Serge Hallyn bugfix]: Letting new_inode() assign inode number to ptmx can collide with hand-assigning inode numbers to ptys. So, hand-assign specific inode number to ptmx node also. - [Serge Hallyn]: Maybe safer to grab root dentry mutex while creating ptmx node - [Bugfix with Serge Hallyn] Replace lookup_one_len() in mknod_ptmx() wih d_alloc_name() (lookup during ->get_sb() locks up system). To simplify patchset, fold the ptmx_dentry patch into this. Changelog[v4]: - Change default permissions of pts/ptmx node to 0000. - Move code for ptmxmode under #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES. Changelog[v3]: - Rename ptmx_mode to ptmxmode (for consistency with 'newinstance') Changelog[v2]: - [H. Peter Anvin] Remove mknod() system call support and create the ptmx node internally. Changelog[v1]: - Earlier version of this patch enabled creating /dev/pts/tty as well. As pointed out by Al Viro and H. Peter Anvin, that is not really necessary. Signed-off-by: Sukadev Bhattiprolu Signed-off-by: Alan Cox Signed-off-by: Linus Torvalds --- fs/devpts/inode.c | 115 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 110 insertions(+), 5 deletions(-) diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index 00530e82673e..8ee9dc2f9e48 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 = { -- 2.30.2