[RFC PATCH 04/27] containers: Allow a process to be forked into a container

David Howells
2019-02-15T16:08:02Z

Allow a single process to be forked directly into a container using a new
syscall, thereby 'booting' the container:

pid_t pid = fork_into_container(int container_fd);

This process will be the 'init' process of the container.

Further attempts to fork into the container will be rejected.

Signed-off-by: David Howells <dhowells@redhat.com>
---

arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
arch/x86/ia32/sys_ia32.c | 2 -
include/linux/cred.h | 3 +
include/linux/nsproxy.h | 7 ++
include/linux/sched/task.h | 3 +
include/linux/syscalls.h | 1
kernel/cred.c | 45 +++++++++++++
kernel/fork.c | 110 ++++++++++++++++++++++++++------
kernel/nsproxy.c | 11 +++
kernel/sys_ni.c | 1
11 files changed, 157 insertions(+), 28 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 3564814a5d21..8666693510f9 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -408,3 +408,4 @@
394 i386 mount_notify sys_mount_notify __ia32_sys_mount_notify
395 i386 sb_notify sys_sb_notify __ia32_sys_sb_notify
396 i386 container_create sys_container_create __ia32_sys_container_create
+397 i386 fork_into_container sys_fork_into_container __ia32_sys_fork_into_container
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index aa6cccbe5271..d40d4790fcb2 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -353,6 +353,7 @@
342 common mount_notify __x64_sys_mount_notify
343 common sb_notify __x64_sys_sb_notify
344 common container_create __x64_sys_container_create
+345 common fork_into_container __x64_sys_fork_into_container

#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/x86/ia32/sys_ia32.c b/arch/x86/ia32/sys_ia32.c
index a43212036257..080d9e21b697 100644
--- a/arch/x86/ia32/sys_ia32.c
+++ b/arch/x86/ia32/sys_ia32.c
@@ -238,5 +238,5 @@ COMPAT_SYSCALL_DEFINE5(x86_clone, unsigned long, clone_flags,
unsigned long, tls_val, int __user *, child_tidptr)
{
return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr,
- tls_val);
+ tls_val, NULL);
}
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 4907c9df86b3..357e743d5d4a 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -23,6 +23,7 @@

struct cred;
struct inode;
+struct container;

/*
* COW Supplementary groups list
@@ -155,7 +156,7 @@ struct cred {

extern void __put_cred(struct cred *);
extern void exit_creds(struct task_struct *);
-extern int copy_creds(struct task_struct *, unsigned long);
+extern int copy_creds(struct task_struct *, unsigned long, struct container *);
extern const struct cred *get_task_cred(struct task_struct *);
extern struct cred *cred_alloc_blank(void);
extern struct cred *prepare_creds(void);
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 2ae1b1a4d84d..81838ae24a92 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -11,6 +11,7 @@ struct ipc_namespace;
struct pid_namespace;
struct cgroup_namespace;
struct fs_struct;
+struct container;

/*
* A structure to contain pointers to all per-process
@@ -63,9 +64,13 @@ extern struct nsproxy init_nsproxy;
* * /
* task_unlock(task);
*
+ * 4. Container namespaces are set at container creation and cannot be
+ * changed.
+ *
*/

-int copy_namespaces(unsigned long flags, struct task_struct *tsk);
+int copy_namespaces(unsigned long flags, struct task_struct *tsk,
+ struct container *dest_container);
void exit_task_namespaces(struct task_struct *tsk);
void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
void free_nsproxy(struct nsproxy *ns);
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 44c6f15800ff..bdff71b0fb66 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -73,7 +73,8 @@ extern void do_group_exit(int);
extern void exit_files(struct task_struct *);
extern void exit_itimers(struct signal_struct *);

-extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *, unsigned long);
+extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *,
+ int __user *, unsigned long, struct container *);
extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
struct task_struct *fork_idle(int);
extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index dac42098c2dd..15e5cc704df3 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -946,6 +946,7 @@ asmlinkage long sys_sb_notify(int dfd, const char __user *path,
asmlinkage long sys_container_create(const char __user *name, unsigned int flags,
unsigned long spare3, unsigned long spare4,
unsigned long spare5);
+asmlinkage long sys_fork_into_container(int containerfd);

/*
* Architecture-specific system calls
diff --git a/kernel/cred.c b/kernel/cred.c
index 21f4a97085b4..f0ee5cec533d 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -313,6 +313,43 @@ struct cred *prepare_exec_creds(void)
return new;
}

+/*
+ * Handle forking a process into a container.
+ */
+static struct cred *copy_container_creds(struct container *dest_container)
+{
+ struct cred *new;
+
+ validate_process_creds();
+
+ new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
+ if (!new)
+ return NULL;
+
+ kdebug("prepare_creds() alloc %p", new);
+
+ memcpy(new, dest_container->cred, sizeof(struct cred));
+
+ atomic_set(&new->usage, 1);
+ set_cred_subscribers(new, 0);
+ get_group_info(new->group_info);
+ get_uid(new->user);
+ get_user_ns(new->user_ns);
+
+#ifdef CONFIG_SECURITY
+ new->security = NULL;
+#endif
+
+ if (security_prepare_creds(new, dest_container->cred, GFP_KERNEL) < 0)
+ goto error;
+ validate_creds(new);
+ return new;
+
+error:
+ abort_creds(new);
+ return NULL;
+}
+
/*
* Copy credentials for the new process created by fork()
*
@@ -322,7 +359,8 @@ struct cred *prepare_exec_creds(void)
* The new process gets the current process's subjective credentials as its
* objective and subjective credentials
*/
-int copy_creds(struct task_struct *p, unsigned long clone_flags)
+int copy_creds(struct task_struct *p, unsigned long clone_flags,
+ struct container *dest_container)
{
struct cred *new;
int ret;
@@ -343,7 +381,10 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
return 0;
}

- new = prepare_creds();
+ if (dest_container)
+ new = copy_container_creds(dest_container);
+ else
+ new = prepare_creds();
if (!new)
return -ENOMEM;

diff --git a/kernel/fork.c b/kernel/fork.c
index 009cf7e63894..71401deb4434 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1385,9 +1385,33 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
return retval;
}

-static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_fs(unsigned long clone_flags, struct task_struct *tsk,
+ struct container *dest_container)
{
struct fs_struct *fs = current->fs;
+
+#ifdef CONFIG_CONTAINERS
+ if (dest_container) {
+ fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
+ if (!fs)
+ return -ENOMEM;
+
+ fs->users = 1;
+ fs->in_exec = 0;
+ spin_lock_init(&fs->lock);
+ seqcount_init(&fs->seq);
+ fs->umask = 0022;
+
+ spin_lock(&dest_container->lock);
+ fs->pwd = fs->root = dest_container->root;
+ path_get(&fs->root);
+ path_get(&fs->pwd);
+ spin_unlock(&dest_container->lock);
+ tsk->fs = fs;
+ return 0;
+ }
+#endif
+
if (clone_flags & CLONE_FS) {
/* tsk->fs is already what we want */
spin_lock(&fs->lock);
@@ -1679,7 +1703,8 @@ static __latent_entropy struct task_struct *copy_process(
struct pid *pid,
int trace,
unsigned long tls,
- int node)
+ int node,
+ struct container *dest_container)
{
int retval;
struct task_struct *p;
@@ -1783,7 +1808,7 @@ static __latent_entropy struct task_struct *copy_process(
}
current->flags &= ~PF_NPROC_EXCEEDED;

- retval = copy_creds(p, clone_flags);
+ retval = copy_creds(p, clone_flags, dest_container);
if (retval < 0)
goto bad_fork_free;

@@ -1905,7 +1930,7 @@ static __latent_entropy struct task_struct *copy_process(
retval = copy_files(clone_flags, p);
if (retval)
goto bad_fork_cleanup_semundo;
- retval = copy_fs(clone_flags, p);
+ retval = copy_fs(clone_flags, p, dest_container);
if (retval)
goto bad_fork_cleanup_files;
retval = copy_sighand(clone_flags, p);
@@ -1917,15 +1942,15 @@ static __latent_entropy struct task_struct *copy_process(
retval = copy_mm(clone_flags, p);
if (retval)
goto bad_fork_cleanup_signal;
- retval = copy_namespaces(clone_flags, p);
+ retval = copy_container(clone_flags, p, dest_container);
if (retval)
goto bad_fork_cleanup_mm;
- retval = copy_container(clone_flags, p, NULL);
+ retval = copy_namespaces(clone_flags, p, dest_container);
if (retval)
- goto bad_fork_cleanup_namespaces;
+ goto bad_fork_cleanup_container;
retval = copy_io(clone_flags, p);
if (retval)
- goto bad_fork_cleanup_container;
+ goto bad_fork_cleanup_namespaces;
retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls);
if (retval)
goto bad_fork_cleanup_io;
@@ -2124,10 +2149,10 @@ static __latent_entropy struct task_struct *copy_process(
bad_fork_cleanup_io:
if (p->io_context)
exit_io_context(p);
-bad_fork_cleanup_container:
- exit_container(p);
bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
+bad_fork_cleanup_container:
+ exit_container(p);
bad_fork_cleanup_mm:
if (p->mm)
mmput(p->mm);
@@ -2183,7 +2208,7 @@ struct task_struct *fork_idle(int cpu)
{
struct task_struct *task;
task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
- cpu_to_node(cpu));
+ cpu_to_node(cpu), NULL);
if (!IS_ERR(task)) {
init_idle_pids(task);
init_idle(task, cpu);
@@ -2195,15 +2220,16 @@ struct task_struct *fork_idle(int cpu)
/*
* Ok, this is the main fork-routine.
*
- * It copies the process, and if successful kick-starts
- * it and waits for it to finish using the VM if required.
+ * It copies the process into the specified container, and if successful
+ * kick-starts it and waits for it to finish using the VM if required.
*/
long _do_fork(unsigned long clone_flags,
unsigned long stack_start,
unsigned long stack_size,
int __user *parent_tidptr,
int __user *child_tidptr,
- unsigned long tls)
+ unsigned long tls,
+ struct container *dest_container)
{
struct completion vfork;
struct pid *pid;
@@ -2229,8 +2255,32 @@ long _do_fork(unsigned long clone_flags,
trace = 0;
}

+ if (dest_container) {
+ /* A process spawned into a container doesn't share anything
+ * with the parent other than namespaces.
+ */
+ if (clone_flags & (CLONE_CHILD_CLEARTID |
+ CLONE_CHILD_SETTID |
+ CLONE_FILES |
+ CLONE_FS |
+ CLONE_IO |
+ CLONE_PARENT |
+ CLONE_PARENT_SETTID |
+ CLONE_PTRACE |
+ CLONE_SETTLS |
+ CLONE_SIGHAND |
+ CLONE_SYSVSEM |
+ CLONE_THREAD))
+ return -EINVAL;
+
+ /* However, we do have to let kernel threads borrow a VM. */
+ if ((clone_flags & CLONE_VM) && current->mm)
+ return -EINVAL;
+ }
+
p = copy_process(clone_flags, stack_start, stack_size,
- child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
+ child_tidptr, NULL, trace, tls, NUMA_NO_NODE,
+ dest_container);
add_latent_entropy();

if (IS_ERR(p))
@@ -2279,7 +2329,7 @@ long do_fork(unsigned long clone_flags,
int __user *child_tidptr)
{
return _do_fork(clone_flags, stack_start, stack_size,
- parent_tidptr, child_tidptr, 0);
+ parent_tidptr, child_tidptr, 0, NULL);
}
#endif

@@ -2289,14 +2339,14 @@ long do_fork(unsigned long clone_flags,
pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
{
return _do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
- (unsigned long)arg, NULL, NULL, 0);
+ (unsigned long)arg, NULL, NULL, 0, NULL);
}

#ifdef __ARCH_WANT_SYS_FORK
SYSCALL_DEFINE0(fork)
{
#ifdef CONFIG_MMU
- return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0);
+ return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0, NULL);
#else
/* can not support in nommu mode */
return -EINVAL;
@@ -2308,7 +2358,26 @@ SYSCALL_DEFINE0(fork)
SYSCALL_DEFINE0(vfork)
{
return _do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
- 0, NULL, NULL, 0);
+ 0, NULL, NULL, 0, NULL);
+}
+#endif
+
+#ifdef CONFIG_CONTAINERS
+SYSCALL_DEFINE1(fork_into_container, int, containerfd)
+{
+ struct fd f = fdget(containerfd);
+ int ret;
+
+ if (!f.file)
+ return -EBADF;
+ ret = -EINVAL;
+ if (is_container_file(f.file)) {
+ struct container *dest_container = f.file->private_data;
+
+ ret = _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0, dest_container);
+ }
+ fdput(f);
+ return ret;
}
#endif

@@ -2336,7 +2405,8 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
unsigned long, tls)
#endif
{
- return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
+ return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls,
+ NULL);
}
#endif

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 4bb5184b3a80..4031075300a4 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -136,12 +136,19 @@ struct nsproxy *create_new_namespaces(unsigned long flags,
* called from clone. This now handles copy for nsproxy and all
* namespaces therein.
*/
-int copy_namespaces(unsigned long flags, struct task_struct *tsk)
+int copy_namespaces(unsigned long flags, struct task_struct *tsk,
+ struct container *dest_container)
{
struct nsproxy *old_ns = tsk->nsproxy;
struct user_namespace *user_ns = task_cred_xxx(tsk, user_ns);
struct nsproxy *new_ns;

+ if (dest_container) {
+ get_nsproxy(dest_container->ns);
+ tsk->nsproxy = dest_container->ns;
+ return 0;
+ }
+
if (likely(!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWCGROUP)))) {
@@ -163,7 +170,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
(CLONE_NEWIPC | CLONE_SYSVSEM))
return -EINVAL;

- new_ns = create_new_namespaces(flags, tsk->nsproxy, user_ns, tsk->fs);
+ new_ns = create_new_namespaces(flags, old_ns, user_ns, tsk->fs);
if (IS_ERR(new_ns))
return PTR_ERR(new_ns);

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index f0455cbb91cf..a23ad529d548 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -144,6 +144,7 @@ COND_SYSCALL(container_create);
/* kernel/exit.c */

/* kernel/fork.c */
+COND_SYSCALL(fork_into_container);

/* kernel/futex.c */
COND_SYSCALL(futex);