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>
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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
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next prev parent 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
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