From: Oleg Nesterov Date: Tue, 22 Mar 2011 23:34:09 +0000 (-0700) Subject: sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code X-Git-Tag: v2.6.39-rc1~264 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=9bfb23fc4a481650e60d22dbe84c0fd5a9d49bba sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code Cleanup: kill the dead code which does nothing but complicates the code and confuses the reader. sys_unshare(CLONE_THREAD/SIGHAND/VM) is not really implemented, and I doubt very much it will ever work. At least, nobody even tried since the original 99d1419d96d7df9cfa56 ("unshare system call -v5: system call handler function") was applied more than 4 years ago. And the code is not consistent. unshare_thread() always fails unconditionally, while unshare_sighand() and unshare_vm() pretend to work if there is nothing to unshare. Remove unshare_thread(), unshare_sighand(), unshare_vm() helpers and related variables and add a simple CLONE_THREAD | CLONE_SIGHAND| CLONE_VM check into check_unshare_flags(). Also, move the "CLONE_NEWNS needs CLONE_FS" check from check_unshare_flags() to sys_unshare(). This looks more consistent and matches the similar do_sysvsem check in sys_unshare(). Note: with or without this patch "atomic_read(mm->mm_users) > 1" can give a false positive due to get_task_mm(). Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Cc: Janak Desai Cc: Daniel Lezcano Cc: "Eric W. Biederman" Cc: KOSAKI Motohiro Cc: Alexey Dobriyan Acked-by: Serge Hallyn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/fork.c b/kernel/fork.c index a8f64f8ec7e1..f2b494d7c557 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1519,38 +1519,24 @@ void __init proc_caches_init(void) } /* - * Check constraints on flags passed to the unshare system call and - * force unsharing of additional process context as appropriate. + * Check constraints on flags passed to the unshare system call. */ -static void check_unshare_flags(unsigned long *flags_ptr) +static int check_unshare_flags(unsigned long unshare_flags) { + if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND| + CLONE_VM|CLONE_FILES|CLONE_SYSVSEM| + CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET)) + return -EINVAL; /* - * 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 namespace, must also unshare filesystem information. + * Not implemented, but pretend it works if there is nothing to + * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND + * needs to unshare vm. */ - 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; + if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) { + /* FIXME: get_task_mm() increments ->mm_users */ + if (atomic_read(¤t->mm->mm_users) > 1) + return -EINVAL; + } return 0; } @@ -1576,34 +1562,6 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp) return 0; } -/* - * Unsharing of 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) && atomic_read(&sigh->count) > 1) - return -EINVAL; - else - return 0; -} - -/* - * Unshare vm if it is being shared - */ -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; -} - /* * Unshare file descriptor table if it is being shared */ @@ -1632,23 +1590,21 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp */ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) { - int err = 0; struct fs_struct *fs, *new_fs = NULL; - struct sighand_struct *new_sigh = NULL; - struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL; struct files_struct *fd, *new_fd = NULL; struct nsproxy *new_nsproxy = NULL; int do_sysvsem = 0; + int err; - check_unshare_flags(&unshare_flags); - - /* Return -EINVAL for all unsupported flags */ - err = -EINVAL; - if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND| - CLONE_VM|CLONE_FILES|CLONE_SYSVSEM| - CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET)) + err = check_unshare_flags(unshare_flags); + if (err) goto bad_unshare_out; + /* + * If unsharing namespace, must also unshare filesystem information. + */ + if (unshare_flags & CLONE_NEWNS) + unshare_flags |= CLONE_FS; /* * CLONE_NEWIPC must also detach from the undolist: after switching * to a new ipc namespace, the semaphore arrays from the old @@ -1656,21 +1612,15 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) */ if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM)) do_sysvsem = 1; - 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_sighand(unshare_flags, &new_sigh))) - goto bad_unshare_cleanup_fs; - if ((err = unshare_vm(unshare_flags, &new_mm))) - goto bad_unshare_cleanup_sigh; + goto bad_unshare_out; if ((err = unshare_fd(unshare_flags, &new_fd))) - goto bad_unshare_cleanup_vm; + goto bad_unshare_cleanup_fs; if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy, new_fs))) goto bad_unshare_cleanup_fd; - if (new_fs || new_mm || new_fd || do_sysvsem || new_nsproxy) { + if (new_fs || new_fd || do_sysvsem || new_nsproxy) { if (do_sysvsem) { /* * CLONE_SYSVSEM is equivalent to sys_exit(). @@ -1696,19 +1646,6 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) spin_unlock(&fs->lock); } - if (new_mm) { - mm = current->mm; - active_mm = current->active_mm; - current->mm = new_mm; - current->active_mm = new_mm; - if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) { - atomic_dec(&mm->oom_disable_count); - atomic_inc(&new_mm->oom_disable_count); - } - activate_mm(active_mm, new_mm); - new_mm = mm; - } - if (new_fd) { fd = current->files; current->files = new_fd; @@ -1725,20 +1662,10 @@ 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_fs: if (new_fs) free_fs_struct(new_fs); -bad_unshare_cleanup_thread: bad_unshare_out: return err; }