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Re: [Qemu-devel] [PATCH 08/12] os-posix: Provide new -runas <uid>:<gid>
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH 08/12] os-posix: Provide new -runas <uid>:<gid> facility |
Date: |
Fri, 13 Apr 2018 17:51:42 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) |
Ian Jackson <address@hidden> writes:
> This allows the caller to specify a uid and gid to use, even if there
> is no corresponding password entry. This will be useful in certain
> Xen configurations.
>
> We don't support just -runas <uid> because: (i) deprivileging without
> calling setgroups would be ineffective (ii) given only a uid we don't
> know what gid we ought to use (since uids may eppear in multiple
> passwd file entries with different gids).
>
> Signed-off-by: Ian Jackson <address@hidden>
> Reviewed-by: Anthony PERARD <address@hidden>
> CC: Paolo Bonzini <address@hidden>
> CC: Markus Armbruster <address@hidden>
> CC: Daniel P. Berrange <address@hidden>
> ---
> v6.1: Fix constness of qemu_strtoul end pointer parameter.
> v6: Use qemu_strtoul for the first strtoul.
> Use error_report rather than fprintf to print usage error message.
> Fix an error message which still referred to . rather than :
> v5: Use : rather than . to separate uid from gid
> v4: Changed to reuse option -runas
> v3: Error messages fixed. Thanks to Peter Maydell and Ross Lagerwall.
> v2: Coding style fixes.
>
> Signed-off-by: Ian Jackson <address@hidden>
> ---
> os-posix.c | 62
> +++++++++++++++++++++++++++++++++++++++++++++++----------
> qemu-options.hx | 3 ++-
> 2 files changed, 53 insertions(+), 12 deletions(-)
>
> diff --git a/os-posix.c b/os-posix.c
> index b9c2343..214f8fb 100644
> --- a/os-posix.c
> +++ b/os-posix.c
> @@ -42,6 +42,8 @@
> #endif
>
> static struct passwd *user_pwd;
> +static uid_t user_uid = (uid_t)-1;
> +static gid_t user_gid = (gid_t)-1;
As we'll see below, @user_pwd->pw_uid, @user_pwd_pw_gid take precedence
over @user_uid, @user_gid. Awkward.
> static const char *chroot_dir;
> static int daemonize;
> static int daemon_pipe;
> @@ -127,6 +129,34 @@ void os_set_proc_name(const char *s)
> #endif
> }
>
> +
> +static bool os_parse_runas_uid_gid(const char *optarg)
> +{
> + unsigned long lv;
> + const char *ep;
> + uid_t got_uid;
> + gid_t got_gid;
> + int rc;
> +
> + errno = 0;
> + rc = qemu_strtoul(optarg, &ep, 0, &lv);
> + got_uid = lv; /* overflow here is ID in C99 */
> + if (rc || *ep != ':' || got_uid != lv || got_uid == (uid_t)-1) {
> + return false;
> + }
> +
> + lv = 0;
Either zero lv before both qemu_strtoul() or neither one.
> + rc = qemu_strtoul(ep + 1, 0, 0, &lv);
> + got_gid = lv; /* overflow here is ID in C99 */
> + if (rc || got_gid != lv || got_gid == (gid_t)-1) {
> + return false;
> + }
> +
> + user_uid = got_uid;
> + user_gid = got_gid;
> + return true;
> +}
> +
> /*
> * Parse OS specific command line options.
> * return 0 if option handled, -1 otherwise
> @@ -144,8 +174,8 @@ void os_parse_cmd_args(int index, const char *optarg)
> #endif
> case QEMU_OPTION_runas:
> user_pwd = getpwnam(optarg);
> - if (!user_pwd) {
> - fprintf(stderr, "User \"%s\" doesn't exist\n", optarg);
> + if (!user_pwd && !os_parse_runas_uid_gid(optarg)) {
> + error_report("User doesn't exist (and is not <uid>:<gid>)");
The error message no longer includes the offending value. Intentional?
Note for later: @user_uid and @user_gid get set only when @user_pwd
remains null.
> exit(1);
> }
> break;
> @@ -165,18 +195,28 @@ void os_parse_cmd_args(int index, const char *optarg)
>
> static void change_process_uid(void)
> {
> - if (user_pwd) {
> - if (setgid(user_pwd->pw_gid) < 0) {
> - fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);
> + if (user_pwd || user_uid != (uid_t)-1) {
> + gid_t intended_gid = user_pwd ? user_pwd->pw_gid : user_gid;
> + uid_t intended_uid = user_pwd ? user_pwd->pw_uid : user_uid;
> + if (setgid(intended_gid) < 0) {
> + fprintf(stderr, "Failed to setgid(%d)\n", intended_gid);
error_report(), please. More of the same below.
> exit(1);
> }
> - if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
> - fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
> - user_pwd->pw_name, user_pwd->pw_gid);
> - exit(1);
> + if (user_pwd) {
> + if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
> + fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
> + user_pwd->pw_name, user_pwd->pw_gid);
> + exit(1);
> + }
> + } else {
> + if (setgroups(1, &user_gid) < 0) {
> + fprintf(stderr, "Failed to setgroups(1, [%d])",
> + user_gid);
> + exit(1);
> + }
> }
> - if (setuid(user_pwd->pw_uid) < 0) {
> - fprintf(stderr, "Failed to setuid(%d)\n", user_pwd->pw_uid);
> + if (setuid(intended_uid) < 0) {
> + fprintf(stderr, "Failed to setuid(%d)\n", intended_uid);
> exit(1);
> }
> if (setuid(0) != -1) {
This function is the only user of @user_pwd, @user_uid, @user_gid.
Have you considered replacing global @user_pwd by @user_uid, @user_gid
and @user_name? --runas with numeric uid and gid would leave @user_name
null.
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 6585058..211f2a6 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -3763,7 +3763,8 @@ ETEXI
>
> #ifndef _WIN32
> DEF("runas", HAS_ARG, QEMU_OPTION_runas, \
> - "-runas user change to user id user just before starting the VM\n",
> + "-runas user change to user id user just before starting the VM\n" \
> + " user can be numeric uid:gid instead\n",
> QEMU_ARCH_ALL)
> #endif
> STEXI
- Re: [Qemu-devel] [PATCH 08/12] os-posix: Provide new -runas <uid>:<gid> facility,
Markus Armbruster <=