struct resolv_context objects provide a temporary resolver context
which does not change during a name lookup operation. Only when the
outmost context is created, the stub resolver configuration is
verified to be current (at present, only against previous res_init
calls). Subsequent attempts to obtain the context will reuse the
result of the initial verification operation.
struct resolv_context can also be extended in the future to store
data which needs to be deallocated during thread cancellation.
Many callers of __res_maybe_init also call _res_hconf_init.
Additional calls to the latter do not hurt because the function
does its work only once. (/etc/hosts.conf is not reloaded or
even checked for changes.) This means that we can simplify the
code by calling _res_hconf_init directly from __res_vinit.
_res_hconf.initialized was not suitable for use in a multi-threaded
environment due to the lack of atomics and memory barriers. Use of it was
also unnecessary because _res_hconf_init did the right thing by using
__libc_once. This patch fixes the glibc-internal uses by just calling
_res_hconf_init unconditionally, and switches to a release MO atomic store
for _res_hconf.initialized to fix the glibc side of the synchronization
problem (which will maintain backward compatibility, but cannot fix the
lack of acquire MO on any glibc-external loads).
[BZ #20477]
* resolv/res_hconf.c (do_init): Use atomic access.
* resolv/res_hconf.h: Add comments.
* nscd/aicache.c (addhstaiX): Call _res_hconf_init unconditionally.
* nss/getXXbyYY_r.c (REENTRANT_NAME): Likewise.
* sysdeps/posix/getaddrinfo.c (gaih_inet): Likewise.
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.
Fixes BZ #15339.
NSS_STATUS_UNAVAIL may mean that a necessary input resource is not
available. This could occur in a number of cases including when the
network is down, system runs out of file descriptors, etc. The
correct differentiator in such a case is the h_errno, which gives the
nature of failure. In case of failures other than a simple 'not
found', we set h_errno as NETDB_INTERNAL and let errno be the
identifier for the exact error.
When glibc is built with --enable-static-nss, the warning that
using NSS symbols requires the nss shared objects to be present
is no longer true, as those symbols are built into libc. Suppress
the warning for those symbols by providing a new macro
(nss_interface_function) for the NSS functions that is defined as
static_link_warning in the normal case, and empty for static NSS.
gethstbynm3_r.
* nscd/gethstbynm2_r.c: Remove.
* nscd/gethstbynm3_r.c: New file.
* nscd/aicache.c (addhstaiX): Use __gethostbyaddr2_r instead of
__gethostbyaddr_r.
* nscd/gethstbyad_r.c: Generate __gethostbyaddr2_r function. Define
__gethostbyaddr_r compatibility wrapper.
* nscd/hstcache.c (cache_addhst): Add ttl parameter. Use it when
determining timeout of entry.
(lookup): Take new parameter and pass it to __gethostbyname3_r and
__gethostbyaddr2_r.
(addhstbyX): Pass reference to variable for TTL to lookup and
cache_addhst.
* nss/Versions [glibc] (GLIBC_PRIVATE): Export __nss_passwd_lookup2,
__nss_group_lookup2, __nss_hosts_lookup2, __nss_services_lookup2,
and __nss_next2. Remove __nss_services_lookup.
* nss/XXX-lookup.c: Name function now *_lookup2. Add new parameter.
Add compat wrapper.
* nss/getXXbyYY_r.c: Changes to call new *_lookup2 functions and
__nss_next2.
* nss/getXXent_r.c: Likewise.
* nss/getnssent_r.c: Likewise.
* nss/nsswitch.c (__nss_lookup): Add new parameter. If first function
does not exist in module, try the optional second name.
(__nss_next2): New function.
(__nss_next): Now wrapper around __nss_next2.
* nss/nsswitch.h: Adjust __nss_lookup prototype.
Declare __nss_next2.
Adjust definition of db_lookup_function type.
* nss/service-lookup.c: Define NO_COMPAT.
* include/netdb.h: Declare __gethostbyaddr2_r and __gethostbyname3_r.
* inet/ether_hton.c: Use __nss_next2 instead of __nss_next.
* inet/ether_ntoh.c: Likewise.
* sunrpc/netname.c: Likewise.
* sunrpc/publickey.c: Likewise.
* inet/getnetgrent.c: Likewise. Adjust calls to __nss_lookup.
* inet/gethstbyad_r.c (DB_LOOKUP_FCT): Change to __nss_hosts_lookup2.
* inet/gethstbynm2_r.c (DB_LOOKUP_FCT): Likewise.
* inet/gethstbynm_r.c (DB_LOOKUP_FCT): Likewise.
* inet/gethstent_r.c (DB_LOOKUP_FCT): Likewise.
* nscd/aicache.c (addhstaiX): Fix default TTL handling.
* inet/getnetgrent.c (setup): Encrypt static pointer.
2004-05-25 Ulrich Drepper <drepper@redhat.com>
* nss/digits_dots.c (__nss_hostname_digits_dots): Remove typep and
flags parameter, convert afp to simple int parameter. Adjust code.
typep was never != NULL and flags therefore also unused. *afp is
never modified.
* nss/nsswitch.h: Adjust __nss_hostname_digits_dots prototype.
* nss/getXXbyYY.c: Remove HAVE_TYPE handling. Adjust af parameter
handling for __nss_hostname_digits_dots calls.
* nss/getXXbyYY_r.c: Likewise.
* elf/dl-load.c (_dl_map_object_from_fd): Map DSOs with MAP_DENYWRITE.
2004-02-26 Ulrich Drepper <drepper@redhat.com>
* nss/getXXbyYY_r.c: Pass result also to the nscd_* function. Don't
set *result here.
* nscd/nscd_proto.h: Add new argument for pointer to result pointer
to all nscd_* functions.
* nscd/nscd_getgr_r.c (nscd_getgr_r): Add new parameter. Store result
pointer in the address provided by the new parameter if successful.
Otherwise store NULL. Return zero if no entry found.
(__nscd_getgrnam_r, __nscd_getgrgid_r): Add new parameter and pass
it on.
* nscd/nscd_gethst_r.c (nscd_gethst_r): Add new parameter. Store
result pointer in the address provided by the new parameter if
successful. Otherwise store NULL. Return zero if no entry found.
(__nscd_gethostbyname_r, __nscd_gethostbyname2_r,
__nscd_gethostbyaddr_r): Add new parameter and pass it on.
* nscd/nscd_getpw_r.c (nscd_getpw_r): Add new parameter. Store result
pointer in the address provided by the new parameter if successful.
Otherwise store NULL. Return zero if no entry found.
(__nscd_getpwnam_r, __nscd_getpwuid_r): Add new parameter and pass
it on.
2003-09-04 Ulrich Drepper <drepper@redhat.com>
* nss/getXXbyYY.c (FUNCTION_NAME): Add a few casts. Remove
unnecessary errno handling.
* nss/getXXbyYY_r.c (INTERNAL): Use better variable name.
Initialize it in all cases. Change it to be a bit more like the
code we had before.
2003-09-03 Ulrich Drepper <drepper@redhat.com>
* nss/getXXbyYY_r.c (INTERNAL): Explicitly set errno and avoid
returning ERANGE if this wasn't intended.
* sysdeps/posix/getaddrinfo.c (gaih_inet): Set no_inet6_date alse
if only PF_INET address is needed.
* nss/getXXbyYY_r.c: Make sure we always return a nonzero value in
case of an error.
when using h_errno and it's not set to NETDB_INTERNAL.
* nss/getXXbyYY_r.c [NEED_H_ERRNO]: Likewise.
* Makefile ($(common-objpfx)testrun.sh): New target.
(others): Depend on it.
(postclean-generated): Append it.
2002-08-27 Ulrich Drepper <drepper@redhat.com>
* nss/getXXbyYY_r.c (REENTRANT_NAME): If no service is available
set h_errno to NO_RECOVERY [PR libc/4360].
