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NSS: Implement group merging support.

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https://sourceware.org/glibc/wiki/Proposals/GroupMerging

== Justification ==
It is common today for users to rely on centrally-managed user stores for
handling their user accounts. However, much software existing today does
not have an innate understanding of such accounts. Instead, they commonly
rely on membership in known groups for managing access-control (for
example the "wheel" group on Fedora and RHEL systems or the "adm" group
on Debian-derived systems). In the present incarnation of nsswitch, the
only way to have such groups managed by a remote user store such as
FreeIPA or Active Directory would be to manually remove the groups from
/etc/group on the clients so that nsswitch would then move past nss_files
and into the SSSD, nss-ldap or other remote user database.

== Solution ==
With this patch, a new action is introduced for nsswitch:
NSS_ACTION_MERGE. To take advantage of it, one will add [SUCCESS=merge]
between two database entries in the nsswitch.conf file. When a group is
located in the first of the two group entries, processing will continue
on to the next one. If the group is also found in the next entry (and the
group name and GID are an exact match), the member list of the second
entry will be added to the group object to be returned.

== Implementation ==
After each DL_LOOKUP_FN() returns, the next action is checked. If the
function returned NSS_STATUS_SUCCESS and the next action is
NSS_ACTION_MERGE, a copy of the result buffer is saved for the next pass
through the loop. If on this next pass through the loop the database
returns another instance of a group matching both the group name and GID,
the member list is added to the previous list and it is returned as a
single object. If the following database does not contain the same group,
then the original is copied back into the destination buffer.

This patch implements merge functionality only for the group database.
For other databases, there is a default implementation that will return
the EINVAL errno if a merge is requested. The merge functionality can be
implemented for other databases at a later time if such is needed. Each
database must provide a unique implementation of the deep-copy and merge
functions.

If [SUCCESS=merge] is present in nsswitch.conf for a glibc version that
does not support it, glibc will process results up until that operation,
at which time it will return results if it has found them or else will
simply return an error. In practical terms, this ends up behaving like
the remainder of the nsswitch.conf line does not exist.

== Iterators ==
This feature does not modify the iterator functionality from its current
behavior. If getgrnam() or getgrgid() is called, glibc will iterate
through all entries in the `group` line in nsswitch.conf and display the
list of members without attempting to merge them. This is consistent with
the behavior of nss_files where if two separate lines are specified for
the same group in /etc/groups, getgrnam()/getgrgid() will display both.
Clients are already expected to handle this gracefully.

== No Premature Optimizations ==
The following is a list of places that might be eligible for
optimization, but were not overengineered for this initial contribution:
 * Any situation where a merge may occur will result in one malloc() of
   the same size as the input buffer.
 * Any situation where a merge does occur will result in a second
   malloc() to hold the list of pointers to member name strings.
 * The list of members is simply concatenated together and is not tested
   for uniqueness (which is identical to the behavior for nss_files,
   which will simply return identical values if they both exist on the
   line in the file. This could potentially be optimized to reduce space
   usage in the buffer, but it is both complex and computationally
   expensive to do so.

== Testing ==
I performed testing by running the getent utility against my newly-built
glibc and configuring /etc/nsswitch.conf with the following entry:
group: group:      files [SUCCESS=merge] sss

In /etc/group I included the line:
wheel❌10:sgallagh

I then configured my local SSSD using the id_provider=local to respond
with:
wheel:*:10:localuser,localuser2

I then ran `getent group wheel` against the newly-built glibc in
multiple situations and received the expected output as described
above:
 * When SSSD was running.
 * When SSSD was configured in nsswitch.conf but the daemon was not
   running.
 * When SSSD was configured in nsswitch.conf but nss_sss.so.2 was not
   installed on the system.
 * When the order of 'sss' and 'files' was reversed.
 * All of the above with the [SUCCESS=merge] removed (to ensure no
   regressions).
 * All of the above with `getent group 10`.
 * All of the above with `getent group` with and without
   `enumerate=true` set in SSSD.
 * All of the above with and without nscd enabled on the system.
This commit is contained in:
Stephen Gallagher 2016-04-29 22:11:09 -04:00 committed by Carlos O'Donell
parent b65b205fbc
commit ced8f89336
16 changed files with 475 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
ChangeLog
View File

@ -1,3 +1,37 @@
2016-04-29 Stephen Gallagher <sgallagh@redhat.com>
Carlos O'Donell <carlos@redhat.com>
[BZ #19072]
* grp/Makefile (headers): Add grp-merge.h
(routines): Add grp-merge.
* grp/getgrgid_r.c: Include grp-merge.h.
(DEEPCOPY_FN): Define.
(MERGE_FN): Define.
* grp/getgrname_r.c: Include grp-merge.h.
(DEEPCOPY_FN): Define.
(MERGE_FN): Define.
* grp/grp-merge.c: New file.
* grp/grp-merge.h: New file.
* include/grp-merge.h: New file.
* grp/Versions: Define __merge_grp@GLIBC_PRIVATE, and
__copy_grp@GLIBC_PRIVATE.
* manual/nss.texi (Actions in the NSS configuration): Describe
return, continue, and merge.
* nscd/getgrgid_r.c: Include grp/grp-merge.h.
(DEEPCOPY_FN): Define.
(MERGE_FN): Define.
* nscd/getgrnam_r.c: Include grp/grp-merge.h.
(DEEPCOPY_FN): Define.
(MERGE_FN): Define.
* nss/getXXbyYY_r.c [!DEEPCOPY_FN]: Define __copy_einval.
[!MERGE_FN]: Define __merge_einval.
(CHECK_MERGE): Define.
(REENTRANT_NAME): Process merge if do_merge is true.
* nss/getnssent_r.c (__nss_setent): Process NSS_ACTION_MERGE.
(__nss_getent_r): Likewise.
* nss/nsswitch.c (nss_parse_service_list): Likewise.
* nss/nsswitch.h (lookup_actions): Define NSS_ACTION_MERGE.
2016-04-29 Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ #20012]

8
NEWS
View File

@ -25,6 +25,14 @@ Version 2.24
1990s and never part of POSIX. Application code should use the int type
instead of “union wait”.
* A new NSS action is added to facilitate large distributed system
administration. The action, MERGE, allows remote user stores like LDAP
to be merged into local user stores like /etc/groups in order to provide
easy to use, updated, and managed sets of merged credentials. The new
action can be used by configuring it in /etc/nsswitch.conf:
group: files [SUCCESS=merge] nis
Implemented by Stephen Gallagher (Red Hat).
Security related changes:
* An unnecessary stack copy in _nss_dns_getnetbyname_r was removed. It

5
grp/Makefile
View File

@ -22,11 +22,12 @@ subdir := grp
include ../Makeconfig
headers := grp.h
headers := grp.h grp-merge.h
routines := fgetgrent initgroups setgroups \
getgrent getgrgid getgrnam putgrent \
getgrent_r getgrgid_r getgrnam_r fgetgrent_r
getgrent_r getgrgid_r getgrnam_r fgetgrent_r \
grp-merge
tests := testgrp tst-putgrent

3
grp/Versions
View File

@ -28,4 +28,7 @@ libc {
# g*
getgrouplist;
}
GLIBC_PRIVATE {
__merge_grp; __copy_grp;
}
}

3
grp/getgrgid_r.c
View File

@ -18,6 +18,7 @@
#include <grp.h>
#include <grp-merge.h>
#define LOOKUP_TYPE struct group
#define FUNCTION_NAME getgrgid
@ -25,5 +26,7 @@
#define ADD_PARAMS gid_t gid
#define ADD_VARIABLES gid
#define BUFLEN NSS_BUFLEN_GROUP
#define DEEPCOPY_FN __copy_grp
#define MERGE_FN __merge_grp
#include <nss/getXXbyYY_r.c>

4
grp/getgrnam_r.c
View File

@ -18,6 +18,7 @@
#include <grp.h>
#include <grp-merge.h>
#define LOOKUP_TYPE struct group
#define FUNCTION_NAME getgrnam
@ -25,4 +26,7 @@
#define ADD_PARAMS const char *name
#define ADD_VARIABLES name
#define DEEPCOPY_FN __copy_grp
#define MERGE_FN __merge_grp
#include <nss/getXXbyYY_r.c>

186
grp/grp-merge.c Normal file
View File

@ -0,0 +1,186 @@
/* Group merging implementation.
Copyright (C) 2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <grp.h>
#include <grp-merge.h>
#define BUFCHECK(size) \
({ \
do \
{ \
if (c + (size) > buflen) \
{ \
free (members); \
return ERANGE; \
} \
} \
while (0); \
})
int
internal_function
__copy_grp (const struct group srcgrp, const size_t buflen,
struct group *destgrp, char *destbuf, char **endptr)
{
size_t i;
size_t c = 0;
size_t len;
size_t memcount;
char **members = NULL;
/* Copy the GID. */
destgrp->gr_gid = srcgrp.gr_gid;
/* Copy the name. */
len = strlen (srcgrp.gr_name) + 1;
BUFCHECK (len);
memcpy (&destbuf[c], srcgrp.gr_name, len);
destgrp->gr_name = &destbuf[c];
c += len;
/* Copy the password. */
len = strlen (srcgrp.gr_passwd) + 1;
BUFCHECK (len);
memcpy (&destbuf[c], srcgrp.gr_passwd, len);
destgrp->gr_passwd = &destbuf[c];
c += len;
/* Count all of the members. */
for (memcount = 0; srcgrp.gr_mem[memcount]; memcount++)
;
/* Allocate a temporary holding area for the pointers to the member
contents, including space for a NULL-terminator. */
members = malloc (sizeof (char *) * (memcount + 1));
if (members == NULL)
return ENOMEM;
/* Copy all of the group members to destbuf and add a pointer to each of
them into the 'members' array. */
for (i = 0; srcgrp.gr_mem[i]; i++)
{
len = strlen (srcgrp.gr_mem[i]) + 1;
BUFCHECK (len);
memcpy (&destbuf[c], srcgrp.gr_mem[i], len);
members[i] = &destbuf[c];
c += len;
}
members[i] = NULL;
/* Copy the pointers from the members array into the buffer and assign them
to the gr_mem member of destgrp. */
destgrp->gr_mem = (char **) &destbuf[c];
len = sizeof (char *) * (memcount + 1);
BUFCHECK (len);
memcpy (&destbuf[c], members, len);
c += len;
free (members);
members = NULL;
/* Save the count of members at the end. */
BUFCHECK (sizeof (size_t));
memcpy (&destbuf[c], &memcount, sizeof (size_t));
c += sizeof (size_t);
if (endptr)
*endptr = destbuf + c;
return 0;
}
libc_hidden_def (__copy_grp)
/* Check that the name, GID and passwd fields match, then
copy in the gr_mem array. */
int
internal_function
__merge_grp (struct group *savedgrp, char *savedbuf, char *savedend,
size_t buflen, struct group *mergegrp, char *mergebuf)
{
size_t c, i, len;
size_t savedmemcount;
size_t memcount;
size_t membersize;
char **members = NULL;
/* We only support merging members of groups with identical names and
GID values. If we hit this case, we need to overwrite the current
buffer with the saved one (which is functionally equivalent to
treating the new lookup as NSS_STATUS_NOTFOUND). */
if (mergegrp->gr_gid != savedgrp->gr_gid
|| strcmp (mergegrp->gr_name, savedgrp->gr_name))
return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
/* Get the count of group members from the last sizeof (size_t) bytes in the
mergegrp buffer. */
savedmemcount = (size_t) *(savedend - sizeof (size_t));
/* Get the count of new members to add. */
for (memcount = 0; mergegrp->gr_mem[memcount]; memcount++)
;
/* Create a temporary array to hold the pointers to the member values from
both the saved and merge groups. */
membersize = savedmemcount + memcount + 1;
members = malloc (sizeof (char *) * membersize);
if (members == NULL)
return ENOMEM;
/* Copy in the existing member pointers from the saved group
Note: this is not NULL-terminated yet. */
memcpy (members, savedgrp->gr_mem, sizeof (char *) * savedmemcount);
/* Back up into the savedbuf until we get back to the NULL-terminator of the
group member list. (This means walking back savedmemcount + 1 (char *) pointers
and the member count value.
The value of c is going to be the used length of the buffer backed up by
the member count and further backed up by the size of the pointers. */
c = savedend - savedbuf
- sizeof (size_t)
- sizeof (char *) * (savedmemcount + 1);
/* Add all the new group members, overwriting the old NULL-terminator while
adding the new pointers to the temporary array. */
for (i = 0; mergegrp->gr_mem[i]; i++)
{
len = strlen (mergegrp->gr_mem[i]) + 1;
BUFCHECK (len);
memcpy (&savedbuf[c], mergegrp->gr_mem[i], len);
members[savedmemcount + i] = &savedbuf[c];
c += len;
}
/* Add the NULL-terminator. */
members[savedmemcount + memcount] = NULL;
/* Copy the member array back into the buffer after the member list and free
the member array. */
savedgrp->gr_mem = (char **) &savedbuf[c];
len = sizeof (char *) * membersize;
BUFCHECK (len);
memcpy (&savedbuf[c], members, len);
c += len;
free (members);
members = NULL;
/* Finally, copy the results back into mergebuf, since that's the buffer
that we were provided by the caller. */
return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
}
libc_hidden_def (__merge_grp)

37
grp/grp-merge.h Normal file
View File

@ -0,0 +1,37 @@
/* Group merging implementation.
Copyright (C) 2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#ifndef _GRP_MERGE_H
#define _GRP_MERGE_H 1
#include <grp.h>
/* Duplicate a grp struct (and its members). When no longer needed, the
calling function must free(newbuf). */
int
__copy_grp (const struct group srcgrp, const size_t buflen,
struct group *destgrp, char *destbuf, char **endptr)
internal_function;
/* Merge the member lists of two grp structs together. */
int
__merge_grp (struct group *savedgrp, char *savedbuf, char *savedend,
size_t buflen, struct group *mergegrp, char *mergebuf)
internal_function;
#endif /* _GRP_MERGE_H */

7
include/grp-merge.h Normal file
View File

@ -0,0 +1,7 @@
#ifndef _GRP_MERGE_H
#include <grp/grp-merge.h>
libc_hidden_proto (__copy_grp)
libc_hidden_proto (__merge_grp)
#endif /* _GRP_MERGE_H */

46
manual/nss.texi
View File

@ -180,7 +180,7 @@ where
The case of the keywords is insignificant. The @var{status}
values are the results of a call to a lookup function of a specific
service. They mean
service. They mean:
@ftable @samp
@item success
@ -203,6 +203,50 @@ locked or a server currently cannot accept more connections. The
default action is @code{continue}.
@end ftable
@noindent
The @var{action} values mean:
@ftable @samp
@item return
If the status matches, stop the lookup process at this service
specification. If an entry is available, provide it to the application.
If an error occurred, report it to the application. In case of a prior
@samp{merge} action, the data is combined with previous lookup results,
as explained below.
@item continue
If the status matches, proceed with the lookup process at the next
entry, discarding the result of the current lookup (and any merged
data). An exception is the @samp{initgroups} database and the
@samp{success} status, where @samp{continue} acts like @code{merge}
below.
@item merge
Proceed with the lookup process, retaining the current lookup result.
This action is useful only with the @samp{success} status. If a
subsequent service lookup succeeds and has a matching @samp{return}
specification, the results are merged, the lookup process ends, and the
merged results are returned to the application. If the following service
has a matching @samp{merge} action, the lookup process continues,
retaining the combined data from this and any previous lookups.
After a @code{merge} action, errors from subsequent lookups are ignored,
and the data gathered so far will be returned.
The @samp{merge} only applies to the @samp{success} status. It is
currently implemented for the @samp{group} database and its group
members field, @samp{gr_mem}. If specified for other databases, it
causes the lookup to fail (if the @var{status} matches).
When processing @samp{merge} for @samp{group} membership, the group GID
and name must be identical for both entries. If only one or the other is
a match, the behavior is undefined.
@end ftable
@noindent
If we have a line like

4
nscd/getgrgid_r.c
View File

@ -17,6 +17,7 @@
#include <grp.h>
#include <grp-merge.h>
#define LOOKUP_TYPE struct group
#define FUNCTION_NAME getgrgid
@ -25,6 +26,9 @@
#define ADD_VARIABLES gid
#define BUFLEN NSS_BUFLEN_GROUP
#define DEEPCOPY_FN __copy_grp
#define MERGE_FN __merge_grp
/* We are nscd, so we don't want to be talking to ourselves. */
#undef USE_NSCD

4
nscd/getgrnam_r.c
View File

@ -17,6 +17,7 @@
#include <grp.h>
#include <grp-merge.h>
#define LOOKUP_TYPE struct group
#define FUNCTION_NAME getgrnam
@ -24,6 +25,9 @@
#define ADD_PARAMS const char *name
#define ADD_VARIABLES name
#define DEEPCOPY_FN __copy_grp
#define MERGE_FN __merge_grp
/* We are nscd, so we don't want to be talking to ourselves. */
#undef USE_NSCD

110
nss/getXXbyYY_r.c
View File

@ -131,6 +131,52 @@
# define AF_VAL AF_INET
#endif
/* Set defaults for merge functions that haven't been defined. */
#ifndef DEEPCOPY_FN
static inline int
__copy_einval (LOOKUP_TYPE a,
const size_t b,
LOOKUP_TYPE *c,
char *d,
char **e)
{
return EINVAL;
}
# define DEEPCOPY_FN __copy_einval
#endif
#ifndef MERGE_FN
static inline int
__merge_einval (LOOKUP_TYPE *a,
char *b,
char *c,
size_t d,
LOOKUP_TYPE *e,
char *f)
{
return EINVAL;
}
# define MERGE_FN __merge_einval
#endif
#define CHECK_MERGE(err, status) \
({ \
do \
{ \
if (err) \
{ \
__set_errno (err); \
if (err == ERANGE) \
status = NSS_STATUS_TRYAGAIN; \
else \
status = NSS_STATUS_UNAVAIL; \
break; \
} \
} \
while (0); \
})
/* Type of the lookup function we need here. */
typedef enum nss_status (*lookup_function) (ADD_PARAMS, LOOKUP_TYPE *, char *,
size_t, int * H_ERRNO_PARM
@ -152,13 +198,16 @@ INTERNAL (REENTRANT_NAME) (ADD_PARAMS, LOOKUP_TYPE *resbuf, char *buffer,
static service_user *startp;
static lookup_function start_fct;
service_user *nip;
int do_merge = 0;
LOOKUP_TYPE mergegrp;
char *mergebuf = NULL;
char *endptr = NULL;
union
{
lookup_function l;
void *ptr;
} fct;
int no_more;
int no_more, err;
enum nss_status status = NSS_STATUS_UNAVAIL;
#ifdef USE_NSCD
int nscd_status;
@ -278,9 +327,66 @@ INTERNAL (REENTRANT_NAME) (ADD_PARAMS, LOOKUP_TYPE *resbuf, char *buffer,
&& errno == ERANGE)
break;
if (do_merge)
{
if (status == NSS_STATUS_SUCCESS)
{
/* The previous loop saved a buffer for merging.
Perform the merge now. */
err = MERGE_FN (&mergegrp, mergebuf, endptr, buflen, resbuf,
buffer);
CHECK_MERGE (err,status);
do_merge = 0;
}
else
{
/* If the result wasn't SUCCESS, copy the saved buffer back
into the result buffer and set the status back to
NSS_STATUS_SUCCESS to match the previous pass through the
loop.
* If the next action is CONTINUE, it will overwrite the value
currently in the buffer and return the new value.
* If the next action is RETURN, we'll return the previously-
acquired values.
* If the next action is MERGE, then it will be added to the
buffer saved from the previous source. */
err = DEEPCOPY_FN (mergegrp, buflen, resbuf, buffer, NULL);
CHECK_MERGE (err, status);
status = NSS_STATUS_SUCCESS;
}
}
/* If we were are configured to merge this value with the next one,
save the current value of the group struct. */
if (nss_next_action (nip, status) == NSS_ACTION_MERGE
&& status == NSS_STATUS_SUCCESS)
{
/* Copy the current values into a buffer to be merged with the next
set of retrieved values. */
if (mergebuf == NULL)
{
/* Only allocate once and reuse it for as many merges as we need
to perform. */
mergebuf = malloc (buflen);
if (mergebuf == NULL)
{
__set_errno (ENOMEM);
status = NSS_STATUS_UNAVAIL;
break;
}
}
err = DEEPCOPY_FN (*resbuf, buflen, &mergegrp, mergebuf, &endptr);
CHECK_MERGE (err, status);
do_merge = 1;
}
no_more = __nss_next2 (&nip, REENTRANT_NAME_STRING,
REENTRANT2_NAME_STRING, &fct.ptr, status, 0);
}
free (mergebuf);
mergebuf = NULL;
#ifdef HANDLE_DIGITS_DOTS
done:

21
nss/getnssent_r.c
View File

@ -79,7 +79,18 @@ __nss_setent (const char *func_name, db_lookup_function lookup_fct,
else
status = DL_CALL_FCT (fct.f, (0));
/* This is a special-case. When [SUCCESS=merge] is in play,
_nss_next2() will skip to the next database. Due to the
implementation of that function, we can't know whether we're
in an enumeration or an individual lookup, which behaves
differently with regards to merging. We'll treat SUCCESS as
an indication to start the enumeration at this database. */
if (nss_next_action (*nip, status) == NSS_ACTION_MERGE)
no_more = 1;
else
no_more = __nss_next2 (nip, func_name, NULL, &fct.ptr, status, 0);
if (is_last_nip)
*last_nip = *nip;
}
@ -175,6 +186,16 @@ __nss_getent_r (const char *getent_func_name,
do
{
/* This is a special-case. When [SUCCESS=merge] is in play,
_nss_next2() will skip to the next database. Due to the
implementation of that function, we can't know whether we're
in an enumeration or an individual lookup, which behaves
differently with regards to merging. We'll treat SUCCESS as
an indication to return the results here. */
if (status == NSS_STATUS_SUCCESS
&& nss_next_action (*nip, status) == NSS_ACTION_MERGE)
no_more = 1;
else
no_more = __nss_next2 (nip, getent_func_name, NULL, &fct.ptr,
status, 0);

3
nss/nsswitch.c
View File

@ -712,6 +712,9 @@ nss_parse_service_list (const char *line)
else if (line - name == 8
&& __strncasecmp (name, "CONTINUE", 8) == 0)
action = NSS_ACTION_CONTINUE;
else if (line - name == 5
&& __strncasecmp (name, "MERGE", 5) == 0)
action = NSS_ACTION_MERGE;
else
goto finish;

3
nss/nsswitch.h
View File

@ -32,7 +32,8 @@
typedef enum
{
NSS_ACTION_CONTINUE,
NSS_ACTION_RETURN
NSS_ACTION_RETURN,
NSS_ACTION_MERGE
} lookup_actions;