From 8280d16172243702ed43432f826ca6130edb4086 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Tue, 21 Aug 2012 12:11:46 -0400 Subject: [PATCH] new helper: replace_fd() analog of dup2(), except that it takes struct file * as source. Signed-off-by: Al Viro --- fs/exec.c | 11 +---- fs/file.c | 103 ++++++++++++++++++++++++++++--------------- include/linux/file.h | 1 + 3 files changed, 70 insertions(+), 45 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index f2b6af585d4a..3fc74681cc6c 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -2041,23 +2041,14 @@ static void wait_for_dump_helpers(struct file *file) static int umh_pipe_setup(struct subprocess_info *info, struct cred *new) { struct file *files[2]; - struct fdtable *fdt; struct coredump_params *cp = (struct coredump_params *)info->data; - struct files_struct *cf = current->files; int err = create_pipe_files(files, 0); if (err) return err; cp->file = files[1]; - sys_close(0); - fd_install(0, files[0]); - spin_lock(&cf->file_lock); - fdt = files_fdtable(cf); - __set_open_fd(0, fdt); - __clear_close_on_exec(0, fdt); - spin_unlock(&cf->file_lock); - + replace_fd(0, files[0], 0); /* and disallow core files too */ current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1}; diff --git a/fs/file.c b/fs/file.c index 7f29544755d0..a7bbe0324478 100644 --- a/fs/file.c +++ b/fs/file.c @@ -821,12 +821,76 @@ bool get_close_on_exec(unsigned int fd) return res; } +static int do_dup2(struct files_struct *files, + struct file *file, unsigned fd, unsigned flags) +{ + struct file *tofree; + struct fdtable *fdt; + + /* + * We need to detect attempts to do dup2() over allocated but still + * not finished descriptor. NB: OpenBSD avoids that at the price of + * extra work in their equivalent of fget() - they insert struct + * file immediately after grabbing descriptor, mark it larval if + * more work (e.g. actual opening) is needed and make sure that + * fget() treats larval files as absent. Potentially interesting, + * but while extra work in fget() is trivial, locking implications + * and amount of surgery on open()-related paths in VFS are not. + * FreeBSD fails with -EBADF in the same situation, NetBSD "solution" + * deadlocks in rather amusing ways, AFAICS. All of that is out of + * scope of POSIX or SUS, since neither considers shared descriptor + * tables and this condition does not arise without those. + */ + fdt = files_fdtable(files); + tofree = fdt->fd[fd]; + if (!tofree && fd_is_open(fd, fdt)) + goto Ebusy; + get_file(file); + rcu_assign_pointer(fdt->fd[fd], file); + __set_open_fd(fd, fdt); + if (flags & O_CLOEXEC) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + spin_unlock(&files->file_lock); + + if (tofree) + filp_close(tofree, files); + + return fd; + +Ebusy: + spin_unlock(&files->file_lock); + return -EBUSY; +} + +int replace_fd(unsigned fd, struct file *file, unsigned flags) +{ + int err; + struct files_struct *files = current->files; + + if (!file) + return __close_fd(files, fd); + + if (fd >= rlimit(RLIMIT_NOFILE)) + return -EMFILE; + + spin_lock(&files->file_lock); + err = expand_files(files, fd); + if (unlikely(err < 0)) + goto out_unlock; + return do_dup2(files, file, fd, flags); + +out_unlock: + spin_unlock(&files->file_lock); + return err; +} + SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags) { int err = -EBADF; - struct file * file, *tofree; - struct files_struct * files = current->files; - struct fdtable *fdt; + struct file *file; + struct files_struct *files = current->files; if ((flags & ~O_CLOEXEC) != 0) return -EINVAL; @@ -844,38 +908,7 @@ SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags) goto Ebadf; goto out_unlock; } - /* - * We need to detect attempts to do dup2() over allocated but still - * not finished descriptor. NB: OpenBSD avoids that at the price of - * extra work in their equivalent of fget() - they insert struct - * file immediately after grabbing descriptor, mark it larval if - * more work (e.g. actual opening) is needed and make sure that - * fget() treats larval files as absent. Potentially interesting, - * but while extra work in fget() is trivial, locking implications - * and amount of surgery on open()-related paths in VFS are not. - * FreeBSD fails with -EBADF in the same situation, NetBSD "solution" - * deadlocks in rather amusing ways, AFAICS. All of that is out of - * scope of POSIX or SUS, since neither considers shared descriptor - * tables and this condition does not arise without those. - */ - err = -EBUSY; - fdt = files_fdtable(files); - tofree = fdt->fd[newfd]; - if (!tofree && fd_is_open(newfd, fdt)) - goto out_unlock; - get_file(file); - rcu_assign_pointer(fdt->fd[newfd], file); - __set_open_fd(newfd, fdt); - if (flags & O_CLOEXEC) - __set_close_on_exec(newfd, fdt); - else - __clear_close_on_exec(newfd, fdt); - spin_unlock(&files->file_lock); - - if (tofree) - filp_close(tofree, files); - - return newfd; + return do_dup2(files, file, newfd, flags); Ebadf: err = -EBADF; diff --git a/include/linux/file.h b/include/linux/file.h index da84fa0f4579..6239591a6122 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -31,6 +31,7 @@ extern struct file *fget_light(unsigned int fd, int *fput_needed); extern struct file *fget_raw(unsigned int fd); extern struct file *fget_raw_light(unsigned int fd, int *fput_needed); extern int f_dupfd(unsigned int from, struct file *file, unsigned flags); +extern int replace_fd(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 void put_filp(struct file *);