From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTP id D0AF15A0269 for ; Thu, 13 Oct 2022 04:18:52 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1665627532; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DEaOucErDBw5Jtin+7OBzlTXsBbHV+9k4AtSClOwbGs=; b=YpewmoYRC6LXZw0DNuQ0Vnt/DdXTZiVOcvsgfMluTCJuTwMtNbPRSobhhebTvj/Wu62q7O 3o6+gbyaeb89pYI+9ftcsZpFjVknIB3UwbRZaOL2F4SSZ4LxU7Gf/avA1g6YOGX9zVR9zw T7sIUxvJhcTkaipWMvz3fY4ivaGxPFE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-263-FjvCZZ9GPS-nLkZDC8rByA-1; Wed, 12 Oct 2022 22:18:50 -0400 X-MC-Unique: FjvCZZ9GPS-nLkZDC8rByA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A3032185A7A3; Thu, 13 Oct 2022 02:18:39 +0000 (UTC) Received: from maya.cloud.tilaa.com (ovpn-208-3.brq.redhat.com [10.40.208.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C3932414A809; Thu, 13 Oct 2022 02:18:33 +0000 (UTC) Date: Thu, 13 Oct 2022 04:18:29 +0200 From: Stefano Brivio To: David Gibson Subject: Re: [PATCH 09/10] isolation: Only configure UID/GID mappings in userns when spawning shell Message-ID: <20221013041829.252980e1@elisabeth> In-Reply-To: <20221011054018.1449506-10-david@gibson.dropbear.id.au> References: <20221011054018.1449506-1-david@gibson.dropbear.id.au> <20221011054018.1449506-10-david@gibson.dropbear.id.au> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: 7HX6TIMXVCLRBCGPYR6ZYKRQCMRFF566 X-Message-ID-Hash: 7HX6TIMXVCLRBCGPYR6ZYKRQCMRFF566 X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.3 Precedence: list List-Id: Development discussion and patches for passt Archived-At: <> Archived-At: List-Archive: <> List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Tue, 11 Oct 2022 16:40:17 +1100 David Gibson wrote: > When in passt mode, or pasta mode spawning a command, we create a userns > for ourselves. This is used both to isolate the pasta/passt process itself > and to run the spawned command, if any. > > Since eed17a47 "Handle userns isolation and dropping root at the same time" > we've handled both cases the same, configuring the UID and GID mappings in > the new userns to map whichever UID we're running as to root within the > userns. > > This mapping is desirable when spawning a shell or other command, so that > the user gets a root shell with reasonably clear abilities within the > userns and netns. It's not necessarily essential, though. When not > spawning a shell, it doesn't really have any purpose: passt itself doesn't > need to be root and can operate fine with an unmapped user (using some of > the capabilities we get when entering the userns instead). > > Configuring the uid_map can cause problems if passt is running with any > capabilities in the initial namespace, such as CAP_NET_BIND_SERVICE to > allow it to forward low ports. In this case the kernel makes files in > /proc/pid owned by root rather than the starting user to prevent the user > from interfering with the operation of the capability-enhanced process. > This includes uid_map meaning we are not able to write to it. > > Whether this behaviour is correct in the kernel is debatable, but in any > case we might as well avoid problems by only initializing the user mappings > when we really want them. > > Signed-off-by: David Gibson > --- > conf.c | 3 ++- > isolation.c | 13 ------------- > pasta.c | 16 ++++++++++++++-- > pasta.h | 3 ++- > 4 files changed, 18 insertions(+), 17 deletions(-) > > diff --git a/conf.c b/conf.c > index 1537dbf..b7661b6 100644 > --- a/conf.c > +++ b/conf.c > @@ -1478,7 +1478,8 @@ void conf(struct ctx *c, int argc, char **argv) > if (*netns) { > pasta_open_ns(c, netns); > } else { > - pasta_start_ns(c, argc - optind, argv + optind); > + pasta_start_ns(c, uid, gid, > + argc - optind, argv + optind); > } > } > > diff --git a/isolation.c b/isolation.c > index e1a024d..b94226d 100644 > --- a/isolation.c > +++ b/isolation.c > @@ -207,9 +207,6 @@ void isolate_initial(void) > */ > void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns) > { > - char uidmap[BUFSIZ]; > - char gidmap[BUFSIZ]; > - > /* First set our UID & GID in the original namespace */ > if (setgroups(0, NULL)) { > /* If we don't have CAP_SETGID, this will EPERM */ > @@ -261,16 +258,6 @@ void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns) > err("Couldn't create user namespace: %s", strerror(errno)); > exit(EXIT_FAILURE); > } > - > - /* Configure user and group mappings */ > - snprintf(uidmap, BUFSIZ, "0 %u 1", uid); > - snprintf(gidmap, BUFSIZ, "0 %u 1", gid); > - > - if (write_file("/proc/self/uid_map", uidmap) || > - write_file("/proc/self/setgroups", "deny") || > - write_file("/proc/self/gid_map", gidmap)) { > - warn("Couldn't configure user namespace"); > - } > } > > /** > diff --git a/pasta.c b/pasta.c > index 0ab2fe4..9666fed 100644 > --- a/pasta.c > +++ b/pasta.c > @@ -166,7 +166,6 @@ static int pasta_setup_ns(void *arg) > { > const struct pasta_setup_ns_arg *a > = (const struct pasta_setup_ns_arg *)arg; > - Unrelated. > if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0")) > warn("Cannot set ping_group_range, ICMP requests might fail"); > > @@ -179,16 +178,20 @@ static int pasta_setup_ns(void *arg) > /** > * pasta_start_ns() - Fork command in new namespace if target ns is not given > * @c: Execution context > + * @uid: UID we're running as in the init namespace > + * @gid: GID we're running as in the init namespace > * @argc: Number of arguments for spawned command > * @argv: Command to spawn and arguments > */ > -void pasta_start_ns(struct ctx *c, int argc, char *argv[]) > +void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, > + int argc, char *argv[]) > { > struct pasta_setup_ns_arg arg = { > .exe = argv[0], > .argv = argv, > }; > char *sh_argv[] = { NULL, NULL }; > + char uidmap[BUFSIZ], gidmap[BUFSIZ]; Should go at the beginning for the usual semi-silly reason. > char ns_fn_stack[NS_FN_STACK_SIZE]; > char sh_arg0[PATH_MAX + 1]; > > @@ -196,7 +199,16 @@ void pasta_start_ns(struct ctx *c, int argc, char *argv[]) > if (!c->debug) > c->quiet = 1; > > + /* Configure user and group mappings */ > + snprintf(uidmap, BUFSIZ, "0 %u 1", uid); > + snprintf(gidmap, BUFSIZ, "0 %u 1", gid); > > + if (write_file("/proc/self/uid_map", uidmap) || > + write_file("/proc/self/setgroups", "deny") || > + write_file("/proc/self/gid_map", gidmap)) { > + warn("Couldn't configure user mappings"); > + } > + Excess whitespace. > if (argc == 0) { > arg.exe = getenv("SHELL"); > if (!arg.exe) > diff --git a/pasta.h b/pasta.h > index 02df1f6..a8b9893 100644 > --- a/pasta.h > +++ b/pasta.h > @@ -7,7 +7,8 @@ > #define PASTA_H > > void pasta_open_ns(struct ctx *c, const char *netns); > -void pasta_start_ns(struct ctx *c, int argc, char *argv[]); > +void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, > + int argc, char *argv[]); > void pasta_ns_conf(struct ctx *c); > void pasta_child_handler(int signal); > int pasta_netns_quit_init(struct ctx *c); -- Stefano