From: Andy Lutomirski <luto@kernel.org>
To: Jann Horn <jannh@google.com>
Cc: dancol@google.com, LKML <linux-kernel@vger.kernel.org>,
timmurray@google.com, Joel Fernandes <joelaf@google.com>,
surenb@google.com, Andrew Lutomirski <luto@kernel.org>,
Linux API <linux-api@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [RFC PATCH] Implement /proc/pid/kill
Date: Wed, 31 Oct 2018 21:53:50 -0700 [thread overview]
Message-ID: <CALCETrXYbtVyWE=iKCCyWewVs-sE3i-jHv=6g-s8rV4CDOE6sg@mail.gmail.com> (raw)
In-Reply-To: <CAG48ez01OWYVqEo+Qf65scG7a-48tDM4Gh3BOUKY+-b9g+9itw@mail.gmail.com>
On Wed, Oct 31, 2018 at 9:23 AM Jann Horn <jannh@google.com> wrote:
>
> +linux-api, Andy Lutomirski, Eric Biederman
>
> On Wed, Oct 31, 2018 at 3:12 AM Daniel Colascione <dancol@google.com> wrote:
> > Add a simple proc-based kill interface. To use /proc/pid/kill, just
> > write the signal number in base-10 ASCII to the kill file of the
> > process to be killed: for example, 'echo 9 > /proc/$$/kill'.
>
> This is a kernel API change, you should CC the linux-api list.
>
> I think that getting the semantics of this right might be easier if
> you used an ioctl handler instead of a write handler.
>
> > Semantically, /proc/pid/kill works like kill(2), except that the
> > process ID comes from the proc filesystem context instead of from an
> > explicit system call parameter. This way, it's possible to avoid races
> > between inspecting some aspect of a process and that process's PID
> > being reused for some other process.
> >
> > With /proc/pid/kill, it's possible to write a proper race-free and
> > safe pkill(1). An approximation follows. A real program might use
> > openat(2), having opened a process's /proc/pid directory explicitly,
> > with the directory file descriptor serving as a sort of "process
> > handle".
> >
> > #!/bin/bash
> > set -euo pipefail
> > pat=$1
> > for proc_status in /proc/*/status; do (
> > cd $(dirname $proc_status)
> > readarray proc_argv -d'' < cmdline
> > if ((${#proc_argv[@]} > 0)) &&
> > [[ ${proc_argv[0]} = *$pat* ]];
> > then
> > echo 15 > kill
> > fi
> > ) || true; done
> >
> > Signed-off-by: Daniel Colascione <dancol@google.com>
> > ---
> > fs/proc/base.c | 39 +++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 39 insertions(+)
> >
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 7e9f07bf260d..923d62b21e67 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -205,6 +205,44 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
> > return result;
> > }
> >
> > +static ssize_t proc_pid_kill_write(struct file *file,
> > + const char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + ssize_t res;
> > + int sig;
> > + char buffer[4];
> > +
> > + res = -EINVAL;
> > + if (*ppos != 0)
> > + goto out;
> > +
> > + res = -EINVAL;
> > + if (count > sizeof(buffer) - 1)
> > + goto out;
> > +
> > + res = -EFAULT;
> > + if (copy_from_user(buffer, buf, count))
> > + goto out;
> > +
> > + buffer[count] = '\0';
> > + res = kstrtoint(strstrip(buffer), 10, &sig);
> > + if (res)
> > + goto out;
> > +
> > + res = kill_pid(proc_pid(file_inode(file)), sig, 0);
Indeed, you can't do this from .write unless you manage to pass a cred
struct pointer in. ioctl or a new syscall would be better.
--Andy
next prev parent reply other threads:[~2018-11-01 4:54 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 22:10 [RFC PATCH] Implement /proc/pid/kill Daniel Colascione
2018-10-30 3:21 ` Joel Fernandes
2018-10-30 8:50 ` Daniel Colascione
2018-10-30 10:39 ` Christian Brauner
2018-10-30 10:40 ` Christian Brauner
2018-10-30 10:48 ` Daniel Colascione
2018-10-30 11:04 ` Christian Brauner
2018-10-30 11:12 ` Daniel Colascione
2018-10-30 11:19 ` Christian Brauner
2018-10-31 5:00 ` Eric W. Biederman
2018-10-30 17:01 ` Joel Fernandes
2018-10-30 5:00 ` Aleksa Sarai
2018-10-30 9:05 ` Daniel Colascione
2018-10-30 20:45 ` Aleksa Sarai
2018-10-30 21:42 ` Joel Fernandes
2018-10-30 22:23 ` Aleksa Sarai
2018-10-30 22:33 ` Joel Fernandes
2018-10-30 22:49 ` Aleksa Sarai
2018-10-31 0:42 ` Joel Fernandes
2018-10-31 1:59 ` Daniel Colascione
2018-10-30 23:10 ` Daniel Colascione
2018-10-30 23:23 ` Christian Brauner
2018-10-30 23:55 ` Daniel Colascione
2018-10-31 2:56 ` Aleksa Sarai
2018-10-31 4:24 ` Joel Fernandes
2018-11-01 20:40 ` Joel Fernandes
2018-11-02 9:46 ` Christian Brauner
2018-11-02 14:34 ` Serge E. Hallyn
2018-10-31 0:57 ` Joel Fernandes
2018-10-31 1:56 ` Daniel Colascione
2018-10-31 4:47 ` Eric W. Biederman
2018-10-31 4:44 ` Eric W. Biederman
2018-10-31 12:44 ` Oleg Nesterov
2018-10-31 13:27 ` Daniel Colascione
2018-10-31 15:10 ` Oleg Nesterov
2018-10-31 15:16 ` Daniel Colascione
2018-10-31 15:49 ` Oleg Nesterov
2018-11-01 11:53 ` David Laight
2018-11-01 15:50 ` Daniel Colascione
2018-10-31 14:37 ` [PATCH v2] " Daniel Colascione
2018-10-31 15:05 ` Joel Fernandes
2018-10-31 17:33 ` Aleksa Sarai
2018-10-31 21:47 ` Joel Fernandes
2018-10-31 15:59 ` [PATCH v3] " Daniel Colascione
2018-10-31 17:54 ` Tycho Andersen
2018-10-31 18:00 ` Daniel Colascione
2018-10-31 18:17 ` Tycho Andersen
2018-10-31 19:33 ` Daniel Colascione
2018-10-31 20:06 ` Tycho Andersen
2018-11-01 11:33 ` David Laight
2018-11-12 1:19 ` Eric W. Biederman
2018-10-31 16:22 ` [RFC PATCH] " Jann Horn
2018-11-01 4:53 ` Andy Lutomirski [this message]
2018-11-12 23:13 ` Pavel Machek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CALCETrXYbtVyWE=iKCCyWewVs-sE3i-jHv=6g-s8rV4CDOE6sg@mail.gmail.com' \
--to=luto@kernel.org \
--cc=dancol@google.com \
--cc=ebiederm@xmission.com \
--cc=jannh@google.com \
--cc=joelaf@google.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=surenb@google.com \
--cc=timmurray@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).