[PATCH -mm 1/9] unshare system call : system call handler function sys_unshare

[PATCH -mm 1/9] unshare system call : system call handler function sys_unshare

[JANAK DESAI]

[PATCH -mm 1/9] unshare system call: System call handler function
sys_unshare
                                                                                
Signed-off-by: Janak Desai


 fork.c |  235
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 235 insertions(+)
 
 
diff -Naurp 2.6.15-rc5-mm2/kernel/fork.c
2.6.15-rc5-mm2+patch/kernel/fork.c
--- 2.6.15-rc5-mm2/kernel/fork.c	2005-12-12 03:05:59.000000000 +0000
+++ 2.6.15-rc5-mm2+patch/kernel/fork.c	2005-12-12 19:31:48.000000000
+0000
@@ -1330,3 +1330,238 @@ void __init proc_caches_init(void)
 			sizeof(struct mm_struct), 0,
 			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;
+			put_fs_struct(fs);
+		}
+
+		if (new_ns) {
+			ns = current->namespace;
+			current->namespace = new_ns;
+			put_namespace(ns);
+		}
+
+		if (new_sigh) {
+			sigh = current->sighand;
+			current->sighand = new_sigh;
+			if (atomic_dec_and_test(&sigh->count))
+				kmem_cache_free(sighand_cachep, 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);
+			mmput(mm);
+		}
+
+		if (new_fd) {
+			fd = current->files;
+			current->files = new_fd;
+			put_files_struct(fd);
+		}
+
+		task_unlock(current);
+	}
+
+	return 0;
+
+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;
+}

Re: [PATCH -mm 1/9] unshare system call : system call handler function sys_unshare

[Al Viro]

On Mon, Dec 12, 2005 at 09:59:50PM -0500, JANAK DESAI wrote:
> +		task_lock(current);
> +
> +		if (new_fs) {
> +			fs = current->fs;
> +			current->fs = new_fs;
> +			put_fs_struct(fs);

Nope.  You can't drop those under a spinlock; leave the pointer e.g. in
new_fs and drop everything after task_unlock().  Incidentally, it allows
to merge cleanup for normal and failure exits.