From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f194.google.com ([209.85.215.194]:36536 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728251AbeI0Va1 (ORCPT ); Thu, 27 Sep 2018 17:30:27 -0400 Received: by mail-pg1-f194.google.com with SMTP id d1-v6so2195972pgo.3 for ; Thu, 27 Sep 2018 08:11:45 -0700 (PDT) From: Tycho Andersen To: Kees Cook Cc: linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org, Andy Lutomirski , Oleg Nesterov , "Eric W . Biederman" , "Serge E . Hallyn" , Christian Brauner , Tyler Hicks , Akihiro Suda , Jann Horn , linux-fsdevel@vger.kernel.org, Tycho Andersen , Alexander Viro Subject: [PATCH v7 4/6] files: add a replace_fd_files() function Date: Thu, 27 Sep 2018 09:11:17 -0600 Message-Id: <20180927151119.9989-5-tycho@tycho.ws> In-Reply-To: <20180927151119.9989-1-tycho@tycho.ws> References: <20180927151119.9989-1-tycho@tycho.ws> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Similar to fd_install/__fd_install, we want to be able to replace an fd of an arbitrary struct files_struct, not just current's. We'll use this in the next patch to implement the seccomp ioctl that allows inserting fds into a stopped process' context. v7: new in v7 Signed-off-by: Tycho Andersen CC: Alexander Viro CC: Kees Cook CC: Andy Lutomirski CC: Oleg Nesterov CC: Eric W. Biederman CC: "Serge E. Hallyn" CC: Christian Brauner CC: Tyler Hicks CC: Akihiro Suda --- fs/file.c | 22 +++++++++++++++------- include/linux/file.h | 8 ++++++++ 2 files changed, 23 insertions(+), 7 deletions(-) diff --git a/fs/file.c b/fs/file.c index 7ffd6e9d103d..3b3c5aadaadb 100644 --- a/fs/file.c +++ b/fs/file.c @@ -850,24 +850,32 @@ __releases(&files->file_lock) } int replace_fd(unsigned fd, struct file *file, unsigned flags) +{ + return replace_fd_task(current, fd, file, flags); +} + +/* + * Same warning as __alloc_fd()/__fd_install() here. + */ +int replace_fd_task(struct task_struct *task, unsigned fd, + struct file *file, unsigned flags) { int err; - struct files_struct *files = current->files; if (!file) - return __close_fd(files, fd); + return __close_fd(task->files, fd); - if (fd >= rlimit(RLIMIT_NOFILE)) + if (fd >= task_rlimit(task, RLIMIT_NOFILE)) return -EBADF; - spin_lock(&files->file_lock); - err = expand_files(files, fd); + spin_lock(&task->files->file_lock); + err = expand_files(task->files, fd); if (unlikely(err < 0)) goto out_unlock; - return do_dup2(files, file, fd, flags); + return do_dup2(task->files, file, fd, flags); out_unlock: - spin_unlock(&files->file_lock); + spin_unlock(&task->files->file_lock); return err; } diff --git a/include/linux/file.h b/include/linux/file.h index 6b2fb032416c..f94277fee038 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -11,6 +11,7 @@ #include struct file; +struct task_struct; extern void fput(struct file *); @@ -79,6 +80,13 @@ static inline void fdput_pos(struct fd f) extern int f_dupfd(unsigned int from, struct file *file, unsigned flags); extern int replace_fd(unsigned fd, struct file *file, unsigned flags); +/* + * Warning! This is only safe if you know the owner of the files_struct is + * stopped outside syscall context. It's a very bad idea to use this unless you + * have similar guarantees in your code. + */ +extern int replace_fd_task(struct task_struct *task, unsigned fd, + struct file *file, unsigned flags); extern void set_close_on_exec(unsigned int fd, int flag); extern bool get_close_on_exec(unsigned int fd); extern int get_unused_fd_flags(unsigned flags); -- 2.17.1