Messages in this thread Patch in this message | | | Date | Wed, 12 Oct 2005 12:07:17 -0400 (Eastern Daylight Time) | From | Janak Desai <> | Subject | [PATCH] New System call unshare (try 2) |
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Hi Chris,
Here is the reworked unshare system call patch which attempts to fix problems that you identified with the first incarnation. The patch, against the latest mm tree 2.6.14-rc2-mm2, was tested on single processor i386 system for the following: Don't allow namespace unsharing, if sharing fs (CLONE_FS) Don't allow sighand unsharing if not unsharing vm Don't allow vm unsharing if task cloned with CLONE_THREAD Don't allow vm unsharing if the task is performing async io Successful unsharing of namespace Cloned a task without sharing fs. Performed mounts before and after a call to unshare to verify that the namespace was indeed unshared. Successful unsharing of vm Cloned a task using CLONE_VM, CLONE_SIGHAND and CLONE_FILES. Used a shared memory segment and futex within it to synchronize execution of threads. Verified shared and unshared vm before and after successful unshare call.
Would appreciate feedback.
Thanks.
-Janak
-------------------------------------------------------------------------- diff -Naurp 2.6.14-rc2-mm2/fs/namespace.c 2.6.14-rc2-mm2+unshare/fs/namespace.c --- 2.6.14-rc2-mm2/fs/namespace.c 2005-10-12 02:56:08.000000000 +0000 +++ 2.6.14-rc2-mm2+unshare/fs/namespace.c 2005-10-12 11:46:52.000000000 +0000 @@ -1069,9 +1069,6 @@ int copy_namespace(int flags, struct tas { 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; @@ -1086,6 +1083,28 @@ int copy_namespace(int flags, struct tas return -EPERM; } + new_ns = dup_namespace_struct(tsk); + if (!new_ns) + goto out; + + tsk->namespace = new_ns; + + put_namespace(namespace); + return 0; + +out: + put_namespace(namespace); + return -ENOMEM; +} + +struct namespace *dup_namespace_struct(struct task_struct *tsk) +{ + 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; + new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL); if (!new_ns) goto out; @@ -1134,8 +1153,6 @@ int copy_namespace(int flags, struct tas } up_write(&tsk->namespace->sem); - tsk->namespace = new_ns; - if (rootmnt) mntput(rootmnt); if (pwdmnt) @@ -1143,12 +1160,10 @@ int copy_namespace(int flags, struct tas if (altrootmnt) mntput(altrootmnt); - put_namespace(namespace); - return 0; + return new_ns; out: - put_namespace(namespace); - return -ENOMEM; + return NULL; } asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name, diff -Naurp 2.6.14-rc2-mm2/include/linux/namespace.h 2.6.14-rc2-mm2+unshare/include/linux/namespace.h --- 2.6.14-rc2-mm2/include/linux/namespace.h 2005-10-12 02:56:35.000000000 +0000 +++ 2.6.14-rc2-mm2+unshare/include/linux/namespace.h 2005-10-12 11:45:46.000000000 +0000 @@ -14,6 +14,7 @@ struct namespace { extern int copy_namespace(int, struct task_struct *); extern void __put_namespace(struct namespace *namespace); +extern struct namespace *dup_namespace_struct(struct task_struct *); static inline void put_namespace(struct namespace *namespace) { diff -Naurp 2.6.14-rc2-mm2/kernel/fork.c 2.6.14-rc2-mm2+unshare/kernel/fork.c --- 2.6.14-rc2-mm2/kernel/fork.c 2005-10-12 02:56:39.000000000 +0000 +++ 2.6.14-rc2-mm2+unshare/kernel/fork.c 2005-10-12 13:26:05.000000000 +0000 @@ -448,6 +448,55 @@ void mm_release(struct task_struct *tsk, } } +/* + * Allocate a new mm structure and copy contents from the + * mm structure of the passed in task structure. + */ +static struct mm_struct *dup_mm_struct(struct task_struct *tsk) +{ + struct mm_struct *mm, *oldmm = current->mm; + int err; + + if (!oldmm) + return NULL; + + mm = allocate_mm(); + if (!mm) + goto fail_nomem; + + memcpy(mm, oldmm, sizeof(*mm)); + + if (!mm_init(mm)) + goto fail_nomem; + + if (init_new_context(tsk, mm)) + goto fail_nocontext; + + err = dup_mmap(mm, oldmm); + if (err) + goto free_pt; + + mm->hiwater_rss = get_mm_rss(mm); + mm->hiwater_vm = mm->total_vm; + + return mm; + +free_pt: + mmput(mm); + +fail_nomem: + return NULL; + +fail_nocontext: + /* + * If init_new_context() failed, we cannot use mmput() to free the mm + * because it calls destroy_context() + */ + mm_free_pgd(mm); + free_mm(mm); + return NULL; +} + static int copy_mm(unsigned long clone_flags, struct task_struct * tsk) { struct mm_struct * mm, *oldmm; @@ -482,43 +531,17 @@ static int copy_mm(unsigned long clone_f } retval = -ENOMEM; - mm = allocate_mm(); + mm = dup_mm_struct(tsk); if (!mm) goto fail_nomem; - /* Copy the current MM stuff.. */ - memcpy(mm, oldmm, sizeof(*mm)); - if (!mm_init(mm)) - goto fail_nomem; - - if (init_new_context(tsk,mm)) - goto fail_nocontext; - - retval = dup_mmap(mm, oldmm); - if (retval) - goto free_pt; - - mm->hiwater_rss = get_mm_rss(mm); - mm->hiwater_vm = mm->total_vm; - good_mm: tsk->mm = mm; tsk->active_mm = mm; return 0; -free_pt: - mmput(mm); fail_nomem: return retval; - -fail_nocontext: - /* - * If init_new_context() failed, we cannot use mmput() to free the mm - * because it calls destroy_context() - */ - mm_free_pgd(mm); - free_mm(mm); - return retval; } static inline struct fs_struct *__copy_fs_struct(struct fs_struct *old) @@ -753,6 +776,23 @@ int unshare_files(void) EXPORT_SYMBOL(unshare_files); +/* + * Allocate a new sighand structure and copy contents from the + * sighand of the passed in task structure + */ +static struct sighand_struct *dup_sh_struct(struct task_struct *tsk) +{ + struct sighand_struct *sh; + + sh = kmem_cache_alloc(sighand_cachep, GFP_KERNEL); + if (!sh) + return NULL; + spin_lock_init(&sh->siglock); + atomic_set(&sh->count, 1); + memcpy(sh->action, current->sighand->action, sizeof(sh->action)); + return sh; +} + static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk) { struct sighand_struct *sig; @@ -761,13 +801,10 @@ static inline int copy_sighand(unsigned atomic_inc(¤t->sighand->count); return 0; } - sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL); + sig = dup_sh_struct(tsk); tsk->sighand = sig; if (!sig) return -ENOMEM; - spin_lock_init(&sig->siglock); - atomic_set(&sig->count, 1); - memcpy(sig->action, current->sighand->action, sizeof(sig->action)); return 0; } @@ -1321,3 +1358,164 @@ void __init proc_caches_init(void) sizeof(struct mm_struct), 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL); } + +/* + * Performs sanity checks on the flags passed to the unshare system + * call. + */ +static inline int check_unshare_flags(unsigned long unshare_flags) +{ + int err = -EINVAL; + + if (unshare_flags & ~(CLONE_NEWNS | CLONE_VM | CLONE_SIGHAND)) + goto errout; + + /* + * Shared signal handlers imply shared VM, so if CLONE_SIGHAND is + * set, CLONE_VM must also be set in the system call argument. + */ + if ((unshare_flags & CLONE_SIGHAND) && !(unshare_flags & CLONE_VM)) + goto errout; + + /* + * Cannot unshare namespace if the fs structure is being shared + * through a previous call to clone() + */ + if ((unshare_flags & CLONE_NEWNS) && + (atomic_read(¤t->fs->count) > 1)) + goto errout; + + if (unshare_flags & CLONE_VM) { + /* + * Cannot unshare vm if the signal structure is being shared + * through a previous call to clone() with CLONE_THREAD. + */ + if (atomic_read(¤t->signal->count) > 1) + goto errout; + + /* + * Cannot unshare vm only if the sighand structure is being + * shared through a previous call to clone() + */ + if (!(unshare_flags & CLONE_SIGHAND) && + (atomic_read(¤t->sighand->count) > 1)) + goto errout; + + /* + * If the task is performing async io, unsharing of vm will + * only allow the parent task, with which the vm was being + * shared, to continue async io operations. The async io + * context is not copied to the new, unshared, copy of vm. + * So don't allow unsharing of vm if the process is setup + * to perform async io. + */ + if (current->mm->ioctx_list) + goto errout; + } + return 0; + +errout: + return err; + +} + +/* + * 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, unshare_ns = 0, unshare_mm = 0, unshare_sh = 0; + struct namespace *new_ns = NULL, *ns = current->namespace; + struct mm_struct *new_mm = NULL, *active_mm = NULL, *mm = current->mm; + struct sighand_struct *new_sh = NULL, *sh = current->sighand; + + err = check_unshare_flags(unshare_flags); + if (err) + goto unshare_out; + + if (unshare_flags & CLONE_NEWNS) { + if (ns && atomic_read(&ns->count) > 1) { + err = -EPERM; + if (!capable(CAP_SYS_ADMIN)) + goto unshare_out; + + err = -ENOMEM; + new_ns = dup_namespace_struct(current); + if (!new_ns) + goto unshare_out; + else + unshare_ns = 1; + } + } + + if (unshare_flags & CLONE_VM) { + if (atomic_read(&mm->mm_users) > 1) { + err = -ENOMEM; + new_mm = dup_mm_struct(current); + if (!new_mm) + goto unshare_cleanup_ns; + else { + unshare_mm = 1; + if (unshare_flags & CLONE_SIGHAND) { + if (atomic_read(&sh->count) > 1) { + new_sh = dup_sh_struct(current); + if (!new_sh) + goto unshare_cleanup_mm; + else + unshare_sh = 1; + } + } + } + } + } + + if (unshare_ns) { + task_lock(current); + current->namespace = new_ns; + task_unlock(current); + put_namespace(ns); + } + + if (unshare_mm) { + task_lock(current); + current->min_flt = current->maj_flt = 0; + current->nvcsw = current->nivcsw = 0; + active_mm = current->active_mm; + current->mm = new_mm; + current->active_mm = new_mm; + activate_mm(active_mm, new_mm); + task_unlock(current); + mmput(mm); + } + + if (unshare_sh) { + write_lock_irq(&tasklist_lock); + spin_lock(&sh->siglock); + spin_lock(&new_sh->siglock); + current->sighand = new_sh; + spin_unlock(&new_sh->siglock); + spin_unlock(&sh->siglock); + write_unlock_irq(&tasklist_lock); + + if (atomic_dec_and_test(&sh->count)) + kmem_cache_free(sighand_cachep, sh); + } + + return 0; + +unshare_cleanup_mm: + if (unshare_mm) + mmput(new_mm); + +unshare_cleanup_ns: + if (unshare_ns) + put_namespace(new_ns); + +unshare_out: + return err; +} - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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