With this patch an open() call on /proc/<pid> will give userspace a handle to struct pid of the process associated with /proc/<pid>. This allows to maintain a stable handle on a process. I have been discussing various approaches extensively during technical conferences this year culminating in a long argument with Eric at Linux Plumbers. The general consensus was that having a handle on a process should be something that is very simple and easy to maintain with the option of being extensible via a more advanced api if the need arises. I believe that this patch is the most simple, dumb, and therefore maintainable solution.
[1]: https://lkml.org/lkml/2018/10/30/118 Cc: "Eric W. Biederman" <ebied...@xmission.com> Cc: Serge Hallyn <se...@hallyn.com> Cc: Jann Horn <ja...@google.com> Cc: Kees Cook <keesc...@chromium.org> Cc: Andy Lutomirsky <l...@kernel.org> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Oleg Nesterov <o...@redhat.com> Cc: Aleksa Sarai <cyp...@cyphar.com> Cc: Al Viro <v...@zeniv.linux.org.uk> Signed-off-by: Christian Brauner <christ...@brauner.io> --- Changelog: v1: - remove ioctl() to signal processes and replace with a dedicated syscall in the next patch --- fs/proc/base.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/proc/base.c b/fs/proc/base.c index ce3465479447..6365a4fea314 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3032,10 +3032,27 @@ static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx) tgid_base_stuff, ARRAY_SIZE(tgid_base_stuff)); } +static int proc_tgid_open(struct inode *inode, struct file *file) +{ + /* grab reference to struct pid and stash the pointer away */ + file->private_data = get_pid(proc_pid(inode)); + return 0; +} + +static int proc_tgid_release(struct inode *inode, struct file *file) +{ + struct pid *pid = file->private_data; + /* drop reference to struct pid */ + put_pid(pid); + return 0; +} + static const struct file_operations proc_tgid_base_operations = { + .open = proc_tgid_open, .read = generic_read_dir, .iterate_shared = proc_tgid_base_readdir, .llseek = generic_file_llseek, + .release = proc_tgid_release, }; static struct dentry *proc_tgid_base_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags) -- 2.19.1
