[PATCH] unshare system call -v5: unshare namespace

If the namespace structure is being shared, allocate a new one and copy
information from the current, shared, structure.

Signed-off-by: Janak Desai <janak@us.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index ce97bec..a2bef5c 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1325,27 +1325,17 @@ dput_out:
        return retval;
 }
 
-int copy_namespace(int flags, struct task_struct *tsk)
+/*
+ * Allocate a new namespace structure and populate it with contents
+ * copied from the namespace of the passed in task structure.
+ */
+struct namespace *dup_namespace(struct task_struct *tsk, struct fs_struct *fs)
 {
        struct namespace *namespace = tsk->namespace;
        struct namespace *new_ns;
        struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
-       struct fs_struct *fs = tsk->fs;
        struct vfsmount *p, *q;
 
-       if (!namespace)
-               return 0;
-
-       get_namespace(namespace);
-
-       if (!(flags & CLONE_NEWNS))
-               return 0;
-
-       if (!capable(CAP_SYS_ADMIN)) {
-               put_namespace(namespace);
-               return -EPERM;
-       }
-
        new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL);
        if (!new_ns)
                goto out;
@@ -1396,8 +1386,6 @@ int copy_namespace(int flags, struct task_struct *tsk)
        }
        up_write(&namespace_sem);
 
-       tsk->namespace = new_ns;
-
        if (rootmnt)
                mntput(rootmnt);
        if (pwdmnt)
@@ -1405,12 +1393,40 @@ int copy_namespace(int flags, struct task_struct *tsk)
        if (altrootmnt)
                mntput(altrootmnt);
 
-       put_namespace(namespace);
-       return 0;
+out:
+       return new_ns;
+}
+
+int copy_namespace(int flags, struct task_struct *tsk)
+{
+       struct namespace *namespace = tsk->namespace;
+       struct namespace *new_ns;
+       int err = 0;
+
+       if (!namespace)
+               return 0;
+
+       get_namespace(namespace);
+
+       if (!(flags & CLONE_NEWNS))
+               return 0;
+
+       if (!capable(CAP_SYS_ADMIN)) {
+               err = -EPERM;
+               goto out;
+       }
+
+       new_ns = dup_namespace(tsk, tsk->fs);
+       if (!new_ns) {
+               err = -ENOMEM;
+               goto out;
+       }
+
+       tsk->namespace = new_ns;
 
 out:
        put_namespace(namespace);
-       return -ENOMEM;
+       return err;
 }
 
 asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,

diff --git a/include/linux/namespace.h b/include/linux/namespace.h
index 6731977..3abc8e3 100644 (file)
--- a/include/linux/namespace.h
+++ b/include/linux/namespace.h
@@ -15,6 +15,7 @@ struct namespace {
 
 extern int copy_namespace(int, struct task_struct *);
 extern void __put_namespace(struct namespace *namespace);
+extern struct namespace *dup_namespace(struct task_struct *, struct fs_struct *);
 
 static inline void put_namespace(struct namespace *namespace)
 {

diff --git a/kernel/fork.c b/kernel/fork.c
index 598e5c2..07dd241 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1388,16 +1388,21 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
 }
 
 /*
- * Unsharing of namespace for tasks created without CLONE_NEWNS is not
- * supported yet
+ * Unshare the namespace structure if it is being shared
  */
-static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp)
+static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp, struct fs_struct *new_fs)
 {
        struct namespace *ns = current->namespace;
 
        if ((unshare_flags & CLONE_NEWNS) &&
-           (ns && atomic_read(&ns->count) > 1))
-               return -EINVAL;
+           (ns && atomic_read(&ns->count) > 1)) {
+               if (!capable(CAP_SYS_ADMIN))
+                       return -EPERM;
+
+               *new_nsp = dup_namespace(current, new_fs ? new_fs : current->fs);
+               if (!*new_nsp)
+                       return -ENOMEM;
+       }
 
        return 0;
 }
@@ -1482,7 +1487,7 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
                goto bad_unshare_out;
        if ((err = unshare_fs(unshare_flags, &new_fs)))
                goto bad_unshare_cleanup_thread;
-       if ((err = unshare_namespace(unshare_flags, &new_ns)))
+       if ((err = unshare_namespace(unshare_flags, &new_ns, new_fs)))
                goto bad_unshare_cleanup_fs;
        if ((err = unshare_sighand(unshare_flags, &new_sigh)))
                goto bad_unshare_cleanup_ns;