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authorEric W. Biederman <ebiederm@xmission.com>2016-06-02 10:29:47 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2016-06-05 10:36:01 -0700
commiteedf265aa003b4781de24cfed40a655a664457e6 (patch)
tree0e37f0a0c6fd15f7528aa3d3bfaec5685f083282 /fs/namei.c
parent049ec1b5a76d34a6980cccdb7c0baeb4eed7a993 (diff)
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devpts: Make each mount of devpts an independent filesystem.
The /dev/ptmx device node is changed to lookup the directory entry "pts" in the same directory as the /dev/ptmx device node was opened in. If there is a "pts" entry and that entry is a devpts filesystem /dev/ptmx uses that filesystem. Otherwise the open of /dev/ptmx fails. The DEVPTS_MULTIPLE_INSTANCES configuration option is removed, so that userspace can now safely depend on each mount of devpts creating a new instance of the filesystem. Each mount of devpts is now a separate and equal filesystem. Reserved ttys are now available to all instances of devpts where the mounter is in the initial mount namespace. A new vfs helper path_pts is introduced that finds a directory entry named "pts" in the directory of the passed in path, and changes the passed in path to point to it. The helper path_pts uses a function path_parent_directory that was factored out of follow_dotdot. In the implementation of devpts: - devpts_mnt is killed as it is no longer meaningful if all mounts of devpts are equal. - pts_sb_from_inode is replaced by just inode->i_sb as all cached inodes in the tty layer are now from the devpts filesystem. - devpts_add_ref is rolled into the new function devpts_ptmx. And the unnecessary inode hold is removed. - devpts_del_ref is renamed devpts_release and reduced to just a deacrivate_super. - The newinstance mount option continues to be accepted but is now ignored. In devpts_fs.h definitions for when !CONFIG_UNIX98_PTYS are removed as they are never used. Documentation/filesystems/devices.txt is updated to describe the current situation. This has been verified to work properly on openwrt-15.05, centos5, centos6, centos7, debian-6.0.2, debian-7.9, debian-8.2, ubuntu-14.04.3, ubuntu-15.10, fedora23, magia-5, mint-17.3, opensuse-42.1, slackware-14.1, gentoo-20151225 (13.0?), archlinux-2015-12-01. With the caveat that on centos6 and on slackware-14.1 that there wind up being two instances of the devpts filesystem mounted on /dev/pts, the lower copy does not end up getting used. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Greg KH <greg@kroah.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Serge Hallyn <serge.hallyn@ubuntu.com> Cc: Willy Tarreau <w@1wt.eu> Cc: Aurelien Jarno <aurelien@aurel32.net> Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> Cc: Jann Horn <jann@thejh.net> Cc: Jiri Slaby <jslaby@suse.com> Cc: Florian Weimer <fw@deneb.enyo.de> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c49
1 files changed, 42 insertions, 7 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 4c4f95ac8aa5..6a82fb7e2127 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1416,21 +1416,28 @@ static void follow_mount(struct path *path)
}
}
+static int path_parent_directory(struct path *path)
+{
+ struct dentry *old = path->dentry;
+ /* rare case of legitimate dget_parent()... */
+ path->dentry = dget_parent(path->dentry);
+ dput(old);
+ if (unlikely(!path_connected(path)))
+ return -ENOENT;
+ return 0;
+}
+
static int follow_dotdot(struct nameidata *nd)
{
while(1) {
- struct dentry *old = nd->path.dentry;
-
if (nd->path.dentry == nd->root.dentry &&
nd->path.mnt == nd->root.mnt) {
break;
}
if (nd->path.dentry != nd->path.mnt->mnt_root) {
- /* rare case of legitimate dget_parent()... */
- nd->path.dentry = dget_parent(nd->path.dentry);
- dput(old);
- if (unlikely(!path_connected(&nd->path)))
- return -ENOENT;
+ int ret = path_parent_directory(&nd->path);
+ if (ret)
+ return ret;
break;
}
if (!follow_up(&nd->path))
@@ -2514,6 +2521,34 @@ struct dentry *lookup_one_len_unlocked(const char *name,
}
EXPORT_SYMBOL(lookup_one_len_unlocked);
+#ifdef CONFIG_UNIX98_PTYS
+int path_pts(struct path *path)
+{
+ /* Find something mounted on "pts" in the same directory as
+ * the input path.
+ */
+ struct dentry *child, *parent;
+ struct qstr this;
+ int ret;
+
+ ret = path_parent_directory(path);
+ if (ret)
+ return ret;
+
+ parent = path->dentry;
+ this.name = "pts";
+ this.len = 3;
+ child = d_hash_and_lookup(parent, &this);
+ if (!child)
+ return -ENOENT;
+
+ path->dentry = child;
+ dput(parent);
+ follow_mount(path);
+ return 0;
+}
+#endif
+
int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
struct path *path, int *empty)
{