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bug#7320: id and groups may lie

From: Jim Meyering
Subject: bug#7320: id and groups may lie
Date: Fri, 27 Apr 2012 15:43:37 +0200

Jim Meyering wrote:
> Marc W. Mengel wrote:
>> This is still broken in RedHat in coreutils-8.4-13
>> All of  "groups" and "id" and "id -G" report groups that you don't have
>> if you list a new/different primary group in /etc/passwd.
>> This is just plain wrong.  "id" and "groups" should list the groups you
>> actually have, not what you would possibly have if you logged out and
>> back in again.
> Thank you for the report.
> It looks like there is indeed a bug.
> I demonstrated it with this:
> With all that, here's the patch I expect to commit:
> diff --git a/src/group-list.c b/src/group-list.c

Here's a complete patch.
Note the lack of a test case.
Even in a root-only test, and briefly, I don't want to change
the password database.

>From 3bcb3ea46d685f499c7a02efb1cbbbf15f858325 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Fri, 27 Apr 2012 13:28:32 +0200
Subject: [PATCH] id,groups: with no user name, print only real and/or
 effective IDs,

... i.e., don't use the getpw* functions.
Before this change, running
groups or id with no user name argument would include a group
name or ID from /etc/passwd.  Thus, under unusual circumstances
(default group is changed, but has not taken effect for a given
session), those programs could print a name or ID that is neither
real nor effective.

To demonstrate, run this:

    echo 'for i in 1 2; do id -G; sleep 1.5; done' \
      |su -s /bin/sh ftp - &
    sleep 1; perl -pi -e 's/^(ftp:x:\d+):(\d+)/$1:9876/' /etc/passwd

Those id -G commands printed the following:

    50 9876

With this change, they print this:


* src/group-list.c (print_group_list): When username is NULL, pass
egid, not getpwuid(ruid)->pw_gid), to xgetgroups, per the API
requirements of xgetgroups callee, mgetgroups.
When not using the password database, don't call getpwuid.
* NEWS (Bug fixes): Mention it.
Originally reported by Brynnen Owen as http://bugs.gnu.org/7320.
Raised again by Marc Mengel in http://bugzilla.redhat.com/816708.
 NEWS             |    8 ++++++++
 THANKS.in        |    2 ++
 src/group-list.c |   14 ++++++++------
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/NEWS b/NEWS
index ef4e508..c50336b 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,14 @@ GNU coreutils NEWS                                    -*- 
outline -*-

 * Noteworthy changes in release ?.? (????-??-??) [?]

+** Bug fixes
+  id and groups, when invoked with no user name argument, would print
+  the default group ID listed in the password database, and sometimes
+  that ID would be neither real nor effective.  For example, in a session
+  for which the default group has just been changed, the new group ID
+  would be listed, even though it is not yet effective.
 ** New features

   fmt now accepts the --goal=WIDTH (-g) option.
diff --git a/THANKS.in b/THANKS.in
index d23f7b3..a7403fd 100644
--- a/THANKS.in
+++ b/THANKS.in
@@ -98,6 +98,7 @@ Brian Silverman                     address@hidden
 Brian Youmans                       address@hidden
 Britton Leo Kerin                   address@hidden
 Bruce Robertson                     address@hidden
+Brynnen Owen                        address@hidden
 Carl Johnson                        address@hidden
 Carl Lowenstein                     address@hidden
 Carl Roth                           address@hidden
@@ -355,6 +356,7 @@ Manfred Hollstein                   address@hidden
 Марк Коренберг                      address@hidden
 Marc Boucher                        address@hidden
 Marc Haber                          address@hidden
+Marc Mengel                         address@hidden
 Marc Lehman                         address@hidden
 Marc Olzheim                        address@hidden
 Marco Franzen                       address@hidden
diff --git a/src/group-list.c b/src/group-list.c
index cf49911..edbb342 100644
--- a/src/group-list.c
+++ b/src/group-list.c
@@ -38,11 +38,14 @@ print_group_list (const char *username,
                   bool use_names)
   bool ok = true;
-  struct passwd *pwd;
+  struct passwd *pwd = NULL;

-  pwd = getpwuid (ruid);
-  if (pwd == NULL)
-    ok = false;
+  if (username)
+    {
+      pwd = getpwuid (ruid);
+      if (pwd == NULL)
+        ok = false;
+    }

   if (!print_group (rgid, use_names))
     ok = false;
@@ -58,8 +61,7 @@ print_group_list (const char *username,
     gid_t *groups;
     int i;

-    int n_groups = xgetgroups (username, (pwd ? pwd->pw_gid : (gid_t) -1),
-                               &groups);
+    int n_groups = xgetgroups (username, (pwd ? pwd->pw_gid : egid), &groups);
     if (n_groups < 0)
         if (username)

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