From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH 1/3] util, conf: Add and use ns_is_init() helper
Date: Mon, 22 May 2023 15:41:17 +1000 [thread overview]
Message-ID: <ZGsAfdXtKmPRqc+f@yekko> (raw)
In-Reply-To: <20230521234158.2769867-2-sbrivio@redhat.com>
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On Mon, May 22, 2023 at 01:41:56AM +0200, Stefano Brivio wrote:
> We'll need this in isolate_initial(). While at it, don't rely on
> BUFSIZ: the earlier issue we had with musl reminded me it's not a
> magic "everything will fit" value. Size the read buffer to what we
> actually need from uid_map.
>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Although...
> ---
> conf.c | 16 +---------------
> util.c | 25 +++++++++++++++++++++++++
> util.h | 2 ++
> 3 files changed, 28 insertions(+), 15 deletions(-)
>
> diff --git a/conf.c b/conf.c
> index 447b000..984c3ce 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -1096,10 +1096,6 @@ static int conf_runas(char *opt, unsigned int *uid, unsigned int *gid)
> */
> static void conf_ugid(char *runas, uid_t *uid, gid_t *gid)
> {
> - const char root_uid_map[] = " 0 0 4294967295";
> - char buf[BUFSIZ];
> - int fd;
> -
> /* If user has specified --runas, that takes precedence... */
> if (runas) {
> if (conf_runas(runas, uid, gid))
> @@ -1116,18 +1112,8 @@ static void conf_ugid(char *runas, uid_t *uid, gid_t *gid)
> return;
>
> /* ...or at least not root in the init namespace... */
> - if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0) {
> - die("Can't determine if we're in init namespace: %s",
> - strerror(errno));
> - }
> -
> - if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
> - strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
> - close(fd);
> + if (!ns_is_init())
> return;
> - }
> -
> - close(fd);
>
> /* ...otherwise use nobody:nobody */
> warn("Don't run as root. Changing to nobody...");
> diff --git a/util.c b/util.c
> index c3e3471..5ec8a6c 100644
> --- a/util.c
> +++ b/util.c
> @@ -390,6 +390,31 @@ int ns_enter(const struct ctx *c)
> return 0;
> }
>
> +/**
> + * ns_is_init() - Is the caller running in the "init" user namespace?
> + *
> + * Return: true if caller is in init, false otherwise, won't return on failure
> + */
> +bool ns_is_init(void)
> +{
> + const char root_uid_map[] = " 0 0 4294967295";
> + char buf[sizeof(root_uid_map) + 1];
> + bool ret = true;
> + int fd;
> +
> + if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0) {
> + die("Can't determine if we're in init namespace: %s",
> + strerror(errno));
> + }
> +
> + if (read(fd, buf, sizeof(root_uid_map)) != sizeof(root_uid_map) ||
I don't think it can go bad in practice, but I think you want to pass
a slightly larger buffer than root_uid_map[], otherwise this test will
succeed if the uid_map contains the expected thing for init, followed
by something else.
> + strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1))
> + ret = false;
> +
> + close(fd);
> + return ret;
> +}
> +
> /**
> * pid_file() - Write PID to file, if requested to do so, and close it
> * @fd: Open PID file descriptor, closed on exit, -1 to skip writing it
> diff --git a/util.h b/util.h
> index ba3e3da..26892aa 100644
> --- a/util.h
> +++ b/util.h
> @@ -8,6 +8,7 @@
>
> #include <stdlib.h>
> #include <stdarg.h>
> +#include <stdbool.h>
>
> #include "log.h"
>
> @@ -216,6 +217,7 @@ char *line_read(char *buf, size_t len, int fd);
> void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
> uint8_t *map, uint8_t *exclude);
> int ns_enter(const struct ctx *c);
> +bool ns_is_init(void);
> void write_pidfile(int fd, pid_t pid);
> int __daemon(int pidfile_fd, int devnull_fd);
> int fls(unsigned long x);
--
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 [this message]
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
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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