[PATCH v7 4/6] files: add a replace_fd_files() function
From: Tycho Andersen <hidden>
Date: 2018-09-27 21:30:27
Also in:
linux-fsdevel, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
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 <redacted> CC: Alexander Viro <viro@zeniv.linux.org.uk> CC: Kees Cook <redacted> CC: Andy Lutomirski <luto@amacapital.net> CC: Oleg Nesterov <oleg@redhat.com> CC: Eric W. Biederman <redacted> CC: "Serge E. Hallyn" <serge@hallyn.com> CC: Christian Brauner <redacted> CC: Tyler Hicks <redacted> CC: Akihiro Suda <redacted> --- 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 <linux/posix_types.h> 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