public inbox for passt-dev@passt.top
 help / color / mirror / code / Atom feed
From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH 2/3] pasta: Detach mount namespace, (re)mount procfs before spawning command
Date: Mon, 22 May 2023 15:42:23 +1000	[thread overview]
Message-ID: <ZGsAv0PLgWxhPOdO@yekko> (raw)
In-Reply-To: <20230521234158.2769867-3-sbrivio@redhat.com>

[-- Attachment #1: Type: text/plain, Size: 2181 bytes --]

On Mon, May 22, 2023 at 01:41:57AM +0200, Stefano Brivio wrote:
> If we want /proc contents to be consistent after pasta spawns a child
> process in a new PID namespace (only for operation without a
> pre-existing namespace), we need to mount /proc after the clone(2)
> call with CLONE_NEWPID, and we enable the child to do that by
> passing, in the same call, the CLONE_NEWNS flag, as described by
> pid_namespaces(7).
> 
> This is not really a remount: in fact, passing MS_REMOUNT to mount(2)
> would make the call fail. We're in another mount namespace now, so
> it's a fresh mount that has the effect of hiding the existing one.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  pasta.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/pasta.c b/pasta.c
> index 3a4d704..b30ce70 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -29,6 +29,7 @@
>  #include <syslog.h>
>  #include <sys/epoll.h>
>  #include <sys/inotify.h>
> +#include <sys/mount.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <fcntl.h>
> @@ -172,6 +173,10 @@ static int pasta_spawn_cmd(void *arg)
>  	const struct pasta_spawn_cmd_arg *a;
>  	sigset_t set;
>  
> +	/* We run in a detached PID and mount namespace: mount /proc over */
> +	if (mount("", "/proc", "proc", 0, NULL))
> +		warn("Couldn't mount /proc: %s", strerror(errno));
> +
>  	if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0"))
>  		warn("Cannot set ping_group_range, ICMP requests might fail");
>  
> @@ -243,7 +248,7 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
>  	pasta_child_pid = do_clone(pasta_spawn_cmd, ns_fn_stack,
>  				   sizeof(ns_fn_stack),
>  				   CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET |
> -				   CLONE_NEWUTS | SIGCHLD,
> +				   CLONE_NEWUTS | CLONE_NEWNS  | SIGCHLD,
>  				   (void *)&arg);
>  
>  	if (pasta_child_pid == -1) {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

  reply	other threads:[~2023-05-22  6:01 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-21 23:41 [PATCH 0/3] Fix pasta-in-pasta operation (and similar) Stefano Brivio
2023-05-21 23:41 ` [PATCH 1/3] util, conf: Add and use ns_is_init() helper Stefano Brivio
2023-05-22  5:41   ` David Gibson
2023-05-22  8:50     ` Stefano Brivio
2023-05-21 23:41 ` [PATCH 2/3] pasta: Detach mount namespace, (re)mount procfs before spawning command Stefano Brivio
2023-05-22  5:42   ` David Gibson [this message]
2023-05-21 23:41 ` [PATCH 3/3] isolation: Initially Keep CAP_SETFCAP if running as UID 0 in non-init Stefano Brivio
2023-05-22  5:48   ` David Gibson

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=ZGsAv0PLgWxhPOdO@yekko \
    --to=david@gibson.dropbear.id.au \
    --cc=passt-dev@passt.top \
    --cc=sbrivio@redhat.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.
Code repositories for project(s) associated with this public inbox

	https://passt.top/passt

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 IMAP folder(s).