1 files changed, 232 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 7f0ab5ee948c..6eb9362775f9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1323,3 +1323,235 @@ void __init proc_caches_init(void)
                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 }
+
+
+/*
+ * Check constraints on flags passed to the unshare system call and
+ * force unsharing of additional process context as appropriate.
+ */
+static inline void check_unshare_flags(unsigned long *flags_ptr)
+{
+        /*
+         * If unsharing a thread from a thread group, must also
+         * unshare vm.
+         */
+        if (*flags_ptr & CLONE_THREAD)
+                *flags_ptr |= CLONE_VM;
+
+        /*
+         * If unsharing vm, must also unshare signal handlers.
+         */
+        if (*flags_ptr & CLONE_VM)
+                *flags_ptr |= CLONE_SIGHAND;
+
+        /*
+         * If unsharing signal handlers and the task was created
+         * using CLONE_THREAD, then must unshare the thread
+         */
+        if ((*flags_ptr & CLONE_SIGHAND) &&
+            (atomic_read(&current->signal->count) > 1))
+                *flags_ptr |= CLONE_THREAD;
+
+        /*
+         * If unsharing namespace, must also unshare filesystem information.
+         */
+        if (*flags_ptr & CLONE_NEWNS)
+                *flags_ptr |= CLONE_FS;
+}
+
+/*
+ * Unsharing of tasks created with CLONE_THREAD is not supported yet
+ */
+static int unshare_thread(unsigned long unshare_flags)
+{
+        if (unshare_flags & CLONE_THREAD)
+                return -EINVAL;
+
+        return 0;
+}
+
+/*
+ * Unsharing of fs info for tasks created with CLONE_FS is not supported yet
+ */
+static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
+{
+        struct fs_struct *fs = current->fs;
+
+        if ((unshare_flags & CLONE_FS) &&
+            (fs && atomic_read(&fs->count) > 1))
+                return -EINVAL;
+
+        return 0;
+}
+
+/*
+ * Unsharing of namespace for tasks created without CLONE_NEWNS is not
+ * supported yet
+ */
+static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp)
+{
+        struct namespace *ns = current->namespace;
+
+        if ((unshare_flags & CLONE_NEWNS) &&
+            (ns && atomic_read(&ns->count) > 1))
+                return -EINVAL;
+
+        return 0;
+}
+
+/*
+ * Unsharing of sighand for tasks created with CLONE_SIGHAND is not
+ * supported yet
+ */
+static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
+{
+        struct sighand_struct *sigh = current->sighand;
+
+        if ((unshare_flags & CLONE_SIGHAND) &&
+            (sigh && atomic_read(&sigh->count) > 1))
+                return -EINVAL;
+        else
+                return 0;
+}
+
+/*
+ * Unsharing of vm for tasks created with CLONE_VM is not supported yet
+ */
+static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
+{
+        struct mm_struct *mm = current->mm;
+
+        if ((unshare_flags & CLONE_VM) &&
+            (mm && atomic_read(&mm->mm_users) > 1))
+                return -EINVAL;
+
+        return 0;
+
+}
+
+/*
+ * Unsharing of files for tasks created with CLONE_FILES is not supported yet
+ */
+static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
+{
+        struct files_struct *fd = current->files;
+
+        if ((unshare_flags & CLONE_FILES) &&
+            (fd && atomic_read(&fd->count) > 1))
+                return -EINVAL;
+
+        return 0;
+}
+
+/*
+ * Unsharing of semundo for tasks created with CLONE_SYSVSEM is not
+ * supported yet
+ */
+static int unshare_semundo(unsigned long unshare_flags, struct sem_undo_list **new_ulistp)
+{
+        if (unshare_flags & CLONE_SYSVSEM)
+                return -EINVAL;
+
+        return 0;
+}
+
+/*
+ * unshare allows a process to 'unshare' part of the process
+ * context which was originally shared using clone.  copy_*
+ * functions used by do_fork() cannot be used here directly
+ * because they modify an inactive task_struct that is being
+ * constructed. Here we are modifying the current, active,
+ * task_struct.
+ */
+asmlinkage long sys_unshare(unsigned long unshare_flags)
+{
+        int err = 0;
+        struct fs_struct *fs, *new_fs = NULL;
+        struct namespace *ns, *new_ns = NULL;
+        struct sighand_struct *sigh, *new_sigh = NULL;
+        struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
+        struct files_struct *fd, *new_fd = NULL;
+        struct sem_undo_list *new_ulist = NULL;
+
+        check_unshare_flags(&unshare_flags);
+
+        if ((err = unshare_thread(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)))
+                goto bad_unshare_cleanup_fs;
+        if ((err = unshare_sighand(unshare_flags, &new_sigh)))
+                goto bad_unshare_cleanup_ns;
+        if ((err = unshare_vm(unshare_flags, &new_mm)))
+                goto bad_unshare_cleanup_sigh;
+        if ((err = unshare_fd(unshare_flags, &new_fd)))
+                goto bad_unshare_cleanup_vm;
+        if ((err = unshare_semundo(unshare_flags, &new_ulist)))
+                goto bad_unshare_cleanup_fd;
+
+        if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist) {
+
+                task_lock(current);
+
+                if (new_fs) {
+                        fs = current->fs;
+                        current->fs = new_fs;
+                        new_fs = fs;
+                }
+
+                if (new_ns) {
+                        ns = current->namespace;
+                        current->namespace = new_ns;
+                        new_ns = ns;
+                }
+
+                if (new_sigh) {
+                        sigh = current->sighand;
+                        current->sighand = new_sigh;
+                        new_sigh = sigh;
+                }
+
+                if (new_mm) {
+                        mm = current->mm;
+                        active_mm = current->active_mm;
+                        current->mm = new_mm;
+                        current->active_mm = new_mm;
+                        activate_mm(active_mm, new_mm);
+                        new_mm = mm;
+                }
+
+                if (new_fd) {
+                        fd = current->files;
+                        current->files = new_fd;
+                        new_fd = fd;
+                }
+
+                task_unlock(current);
+        }
+
+bad_unshare_cleanup_fd:
+        if (new_fd)
+                put_files_struct(new_fd);
+
+bad_unshare_cleanup_vm:
+        if (new_mm)
+                mmput(new_mm);
+
+bad_unshare_cleanup_sigh:
+        if (new_sigh)
+                if (atomic_dec_and_test(&new_sigh->count))
+                        kmem_cache_free(sighand_cachep, new_sigh);
+
+bad_unshare_cleanup_ns:
+        if (new_ns)
+                put_namespace(new_ns);
+
+bad_unshare_cleanup_fs:
+        if (new_fs)
+                put_fs_struct(new_fs);
+
+bad_unshare_cleanup_thread:
+bad_unshare_out:
+        return err;
+}