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Stephen Smalley wrote:
> On Tue, 2009-01-06 at 11:30 -0500, Daniel J Walsh wrote:
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>> Stephen Smalley wrote:
>>> On Tue, 2009-01-06 at 08:51 -0600, Manoj Srivastava wrote:
>>>> On Tue, Jan 06 2009, Daniel J Walsh wrote:
>>>>
>>>>> Manoj Srivastava wrote:
>>>>>> On Mon, Jan 05 2009, Daniel J Walsh wrote:
>>>>>>
>>>>>>> Manoj Srivastava wrote:
>>>>>>>> From: Manoj Srivastava <srivasta@xxxxxxxxxx>
>>>>>>>>
>>>>>>>> Some non-Debian packages (like qmail, shudder) create users not below
>>>>>>>> MIN_UID, but above MAX_UID, in /etc/login.defs (non-system users are
>>>>>>>> supposed to have uids between MIN_UID and MAX_UID.
>>>>>>>>
>>>>>>>> genhomedircon.c:gethomedirs() checks pwent.pw_uid against MIN_UID in
>>>>>>>> /etc/login.defs to exclude system users from generating homedir
>>>>>>>> contexts. But unfortunately it does not check it against MAX_UID
>>>>>>>> setting from the same file.
>>>>>>>>
>>>>>>>> This gets us lines like the following in the
>>>>>>>> contexts/files/file_contexts.homedirs file:
>>>>>>>>
>>>>>>>> ,----
>>>>>>>> | #
>>>>>>>> | # Home Context for user user_u
>>>>>>>> | #
>>>>>>>> | /var/qmail/[^/]*/.+ user_u:object_r:user_home_t:s0
>>>>>>>> | /var/qmail/[^/]*/\.ssh(/.*)? user_u:object_r:user_home_ssh_t:s0
>>>>>>>> | /var/qmail/[^/]*/\.gnupg(/.+)? user_u:object_r:user_gpg_secret_t:s0
>>>>>>>> | /var/qmail/[^/]* -d user_u:object_r:user_home_dir_t:s0
>>>>>>>> | /var/qmail/lost\+found/.* <<none>>
>>>>>>>> | /var/qmail -d system_u:object_r:home_root_t:s0
>>>>>>>> | /var/qmail/\.journal <<none>>
>>>>>>>> | /var/qmail/lost\+found -d system_u:object_r:lost_found_t:s0
>>>>>>>> | /tmp/gconfd-.* -d user_u:object_r:user_tmp_t:s0
>>>>>>>> `----
>>>>>>>>
>>>>>>>> This commit adds checking uid value againt MAX_UID too.
>>>>>>>>
>>>>>>>> Signed-off-by: Manoj Srivastava <srivasta@xxxxxxxxxx>
>>>>>>>> ---
>>>>>>>> src/genhomedircon.c | 22 ++++++++++++++++++----
>>>>>>>> 1 files changed, 18 insertions(+), 4 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/src/genhomedircon.c b/src/genhomedircon.c
>>>>>>>> index ce15807..a5306d7 100644
>>>>>>>> --- a/src/genhomedircon.c
>>>>>>>> +++ b/src/genhomedircon.c
>>>>>>>> @@ -219,8 +219,8 @@ static semanage_list_t *get_home_dirs(genhomedircon_settings_t * s)
>>>>>>>> char *rbuf = NULL;
>>>>>>>> char *path = NULL;
>>>>>>>> long rbuflen;
>>>>>>>> - uid_t temp, minuid = 0;
>>>>>>>> - int minuid_set = 0;
>>>>>>>> + uid_t temp, minuid = 0, maxuid = 0;
>>>>>>>> + int minuid_set = 0, maxuid_set = 0;
>>>>>>>> struct passwd pwstorage, *pwbuf;
>>>>>>>> struct stat buf;
>>>>>>>> int retval;
>>>>>>>> @@ -270,6 +270,16 @@ static semanage_list_t *get_home_dirs(genhomedircon_settings_t * s)
>>>>>>>> }
>>>>>>>> free(path);
>>>>>>>> path = NULL;
>>>>>>>> + path = semanage_findval(PATH_ETC_LOGIN_DEFS, "UID_MAX", NULL);
>>>>>>>> + if (path && *path) {
>>>>>>>> + temp = atoi(path);
>>>>>>>> + if (!maxuid_set || temp > maxuid) {
>>>>>>>> + maxuid = temp;
>>>>>>>> + maxuid_set = 1;
>>>>>>>> + }
>>>>>>>> + }
>>>>>>>> + free(path);
>>>>>>>> + path = NULL;
>>>>>>>>
>>>>>>>> path = semanage_findval(PATH_ETC_LIBUSER, "LU_UIDNUMBER", "=");
>>>>>>>> if (path && *path) {
>>>>>>>> @@ -286,6 +296,10 @@ static semanage_list_t *get_home_dirs(genhomedircon_settings_t * s)
>>>>>>>> minuid = 500;
>>>>>>>> minuid_set = 1;
>>>>>>>> }
>>>>>>>> + if (!maxuid_set) {
>>>>>>>> + maxuid = 60000;
>>>>>>>> + maxuid_set = 1;
>>>>>>>> + }
>>>>>>>>
>>>>>>>> rbuflen = sysconf(_SC_GETPW_R_SIZE_MAX);
>>>>>>>> if (rbuflen <= 0)
>>>>>>>> @@ -295,7 +309,7 @@ static semanage_list_t *get_home_dirs(genhomedircon_settings_t * s)
>>>>>>>> goto fail;
>>>>>>>> setpwent();
>>>>>>>> while ((retval = getpwent_r(&pwstorage, rbuf, rbuflen, &pwbuf)) == 0) {
>>>>>>>> - if (pwbuf->pw_uid < minuid)
>>>>>>>> + if (pwbuf->pw_uid < minuid || pwbuf->pw_uid > maxuid)
>>>>>>>> continue;
>>>>>>>> if (!semanage_list_find(shells, pwbuf->pw_shell))
>>>>>>>> continue;
>>>>>>>> @@ -322,7 +336,7 @@ static semanage_list_t *get_home_dirs(genhomedircon_settings_t * s)
>>>>>>>>
>>>>>>>> /* NOTE: old genhomedircon printed a warning on match */
>>>>>>>> if (hand.matched) {
>>>>>>>> - WARN(s->h_semanage, "%s homedir %s or its parent directory conflicts with a file context already specified in the policy. This usually indicates an incorrectly defined system account. If it is a system account please make sure its uid is less than %u or its login shell is /sbin/nologin.", pwbuf->pw_name, pwbuf->pw_dir, minuid);
>>>>>>>> + WARN(s->h_semanage, "%s homedir %s or its parent directory conflicts with a file context already specified in the policy. This usually indicates an incorrectly defined system account. If it is a system account please make sure its uid is less than %u or greater than %u or its login shell is /sbin/nologin.", pwbuf->pw_name, pwbuf->pw_dir, minuid, maxuid);
>>>>>>>> } else {
>>>>>>>> if (semanage_list_push(&homedir_list, path))
>>>>>>>> goto fail;
>>>>>>> I think the default MAX_UID is not big enough.
>>>>>>>
>>>>>>> Shouldn't it be MAXINT?
>>>>>> Not unless I am misunderstanding the logic here. The way I see
>>>>>> it, the code below:
>>>>>> ,----
>>>>>> | while ((retval = getpwent_r(&pwstorage, rbuf, rbuflen, &pwbuf)) == 0) {
>>>>>> | if (pwbuf->pw_uid < minuid || pwbuf->pw_uid > maxuid)
>>>>>> | continue;
>>>>>> | if (!semanage_list_find(shells, pwbuf->pw_shell))
>>>>>> | continue;
>>>>>> | if (strcmp(pwbuf->pw_dir, "/") == 0)
>>>>>> | continue;
>>>>>> | if (semanage_str_count(pwbuf->pw_dir, '/') <= 1)
>>>>>> | continue;
>>>>>> | if (!(path = strdup(pwbuf->pw_dir))) {
>>>>>> | break;
>>>>>> | }
>>>>>> | /* DO STUFF HERE */
>>>>>> | }
>>>>>> `----
>>>>>>
>>>>>> Does nothing iff: pw_uid < minuid || pw_uid > maxuid, so it
>>>>>> only does things if the UID is in the range legal for non-system users;
>>>>>> and the UID range for system users is UID_MIN < uid < UID_MAX.
>>>>>>
>>>>>> If you change the upper bound to max int, then we will create
>>>>>> the entries for UIDs in the range above 60000 -- which is where the
>>>>>> bletcherous qmail install script places the qmail uid.
>>>>>>
>>>>>> The current behaviour, but not checking the upper bound of the
>>>>>> acceptable user range would be equivalent to the raising the upper
>>>>>> bound to INT_MAX; and indeed, would make this patch redundant.
>>>>>>
>>>>>> From login.defs(5):
>>>>>> ,----
>>>>>> | UID_MAX (number), UID_MIN (number)
>>>>>> | Range of user IDs used for the creation of regular users by
>>>>>> | useradd or newusers.
>>>>>> `----
>>>>>>
>>>>>> Therefore I think that the right thing to do would be to check
>>>>>> for both the upper and the lower bound, not just the lower bound
>>>>>> check, which is all we do now.
>>>>>>
>>>>>> manoj
>>>>> my point being, if I have a legitimate UID > 60000 for a real user and
>>>>> do not define UID_MAX, My account will not work.
>>>>>
>>>>> I do not have a problem with checking UID_MAX, just that the default
>>>>> should be much higer then 60000.
>>>> I just went with the Debian policy default value; 60000 is the
>>>> upper limit of uid's on Debian (and probably most Debian derivative)
>>>> machines, and UID's lager than that are reserved by policy for Debian
>>>> packages to use (after discussion on the development mailing lists).
>>> The same appears to be true in Fedora; UID_MAX is set to 60000 by
>>> default in /etc/login.defs there as well.
>>>
>>>> Having said that, I have no objection to making the default max
>>>> uid a preprocessor constant, which can be tweaked by the
>>>> distributions. Should I send in an updated patch?
>> Talking to Nalin, he thinks this number should be ignored, Imagine a
>> university with > 60000 students or a large government Department (Say
>> DOD), this will cause users with UID 600001 to not work correctly.
>>
>> UID_MAX is just there to tell useradd to give up when trying to find the
>> next available UID to add, it means nothing when you have a network of
>> Users.
>
> This seems similar to the discussion you raised in:
> http://marc.info/?l=selinux&m=122286879230076&w=2
>
> Unfortunately there wasn't any real follow-up at the time.
>
I would like to make a suggestion we add a couple of flags to
/etc/selinux/semanage.conf
# semanage searches the passwd database for parents of home directories
of "real users". semanage uses these values to setup the default file
# context, so that files in the "real users" home directory are labeled
# correctly.
# semanage tries to identify "real users" by looking for
# users with UID greater then UID_MIN as specified in /etc/login.defs.
# UID_MIN defaults to 500. The user must also have a shell specified in
# /etc/shells, excluding /bin/false and /sbin/nologin. On machines with
# thousands of entries in the passwd database, semanage can take a very
# long time to run.
#
# Alternatively semanage will not search the passwd database when you
# specify HOMEPARENT value.
#
# HOMEPARENT takes as its value a colon-separated list of directories
#
# HOMEPARENT=/home:/export/home:/usr/local/home
#
# Specify HOMEEXCLUDE to tell semanage to ignore these directories even
# if they seem to be parents of "real user" accounts
#
# HOMEEXCLUDE=/var/lib
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