[PATCH 1/4] nss: Introduce <nss_module.h>
DJ Delorie
dj@redhat.com
Thu Jun 25 04:04:44 GMT 2020
This provides the struct nss_module type, which combines the old
struct service_library type with the known_function tree, by
statically allocating space for all function pointers.
struct nss_module is fairly large (536 bytes), but it will be
shared across NSS databases. The old known_function handling
had non-some per-function overhead (at least 32 bytes per looked-up
function, but more for long function anmes), so overall, this is not
too bad. Resolving all functions at load time simplifies locking,
and the repeated lookups should be fast because the caches are hot
at this point.
---
malloc/set-freeres.c | 3 +
nss/Makefile | 2 +-
nss/nss_module.c | 300 +++++++++++++++++++++++++++++++++++++++++++
nss/nss_module.h | 152 ++++++++++++++++++++++
4 files changed, 456 insertions(+), 1 deletion(-)
create mode 100644 nss/nss_module.c
create mode 100644 nss/nss_module.h
diff --git a/malloc/set-freeres.c b/malloc/set-freeres.c
index aa80eb64b8..b328cca7c6 100644
--- a/malloc/set-freeres.c
+++ b/malloc/set-freeres.c
@@ -20,6 +20,7 @@
#include <set-hooks.h>
#include <libc-internal.h>
+#include "../nss/nss_module.h"
#include "../libio/libioP.h"
DEFINE_HOOK (__libc_subfreeres, (void));
@@ -41,6 +42,8 @@ __libc_freeres (void)
{
void *const *p;
+ call_function_static_weak (__nss_module_freeres);
+
_IO_cleanup ();
/* We run the resource freeing after IO cleanup. */
diff --git a/nss/Makefile b/nss/Makefile
index 97bab5bb75..5d357eb51e 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -28,7 +28,7 @@ headers := nss.h
routines = nsswitch getnssent getnssent_r digits_dots \
valid_field valid_list_field rewrite_field \
$(addsuffix -lookup,$(databases)) \
- compat-lookup nss_hash
+ compat-lookup nss_hash nss_module
# These are the databases that go through nss dispatch.
# Caution: if you add a database here, you must add its real name
diff --git a/nss/nss_module.c b/nss/nss_module.c
new file mode 100644
index 0000000000..29dc1139c6
--- /dev/null
+++ b/nss/nss_module.c
@@ -0,0 +1,300 @@
+/* Global list of NSS service modules.
+ Copyright (c) 2020 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <nss_module.h>
+
+#include <array_length.h>
+#include <assert.h>
+#include <atomic.h>
+#include <dlfcn.h>
+#include <gnu/lib-names.h>
+#include <libc-lock.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Suffix after .so of NSS service modules. */
+static const char *const __nss_shlib_revision = LIBNSS_FILES_SO + 15;
+
+/* A single-linked list used to implement a mapping from names to NSS
+ modules. (Most systems only use five or so service modules, so a
+ list is sufficient here.) Elements of this list are never freed
+ during normal operation. */
+static struct nss_module *nss_module_list;
+
+/* Covers the list and also loading of individual NSS service
+ modules. */
+__libc_lock_define (static, nss_module_list_lock);
+
+struct nss_module *
+__nss_module_allocate (const char *name, size_t name_length)
+{
+ __libc_lock_lock (nss_module_list_lock);
+
+ struct nss_module *result = NULL;
+ for (struct nss_module *p = nss_module_list; p != NULL; p = p->next)
+ if (strncmp (p->name, name, name_length) == 0
+ && p->name[name_length] == '\0')
+ {
+ /* Return the previously existing object. */
+ result = p;
+ break;
+ }
+
+ if (result == NULL)
+ {
+ /* Allocate a new list entry if the name was not found in the
+ list. */
+ result = malloc (sizeof (*result) + name_length + 1);
+ if (result != NULL)
+ {
+ result->state = nss_module_uninitialized;
+ memcpy (result->name, name, name_length);
+ result->name[name_length] = '\0';
+ result->handle = NULL;
+ result->next = nss_module_list;
+ nss_module_list = result;
+ }
+ }
+
+ __libc_lock_unlock (nss_module_list_lock);
+ return result;
+}
+
+/* Long enough to store the name of any function. */
+typedef char function_name[19];
+
+/* This must be lexicographically sorted and match struct
+ nss_module_functions. */
+static const function_name nss_function_name_array[] =
+ {
+ "endaliasent",
+ "endetherent",
+ "endgrent",
+ "endhostent",
+ "endnetent",
+ "endnetgrent",
+ "endprotoent",
+ "endpwent",
+ "endrpcent",
+ "endservent",
+ "endsgent",
+ "endspent",
+ "getaliasbyname_r",
+ "getaliasent_r",
+ "getcanonname_r",
+ "getetherent_r",
+ "getgrent_r",
+ "getgrgid_r",
+ "getgrnam_r",
+ "gethostbyaddr2_r",
+ "gethostbyaddr_r",
+ "gethostbyname2_r",
+ "gethostbyname3_r",
+ "gethostbyname4_r",
+ "gethostbyname_r",
+ "gethostent_r",
+ "gethostton_r",
+ "getnetbyaddr_r",
+ "getnetbyname_r",
+ "getnetent_r",
+ "getnetgrent_r",
+ "getntohost_r",
+ "getprotobyname_r",
+ "getprotobynumber_r",
+ "getprotoent_r",
+ "getpublickey",
+ "getpwent_r",
+ "getpwnam_r",
+ "getpwuid_r",
+ "getrpcbyname_r",
+ "getrpcbynumber_r",
+ "getrpcent_r",
+ "getsecretkey",
+ "getservbyname_r",
+ "getservbyport_r",
+ "getservent_r",
+ "getsgent_r",
+ "getsgnam_r",
+ "getspent_r",
+ "getspnam_r",
+ "initgroups_dyn",
+ "netname2user",
+ "setaliasent",
+ "setetherent",
+ "setgrent",
+ "sethostent",
+ "setnetent",
+ "setnetgrent",
+ "setprotoent",
+ "setpwent",
+ "setrpcent",
+ "setservent",
+ "setsgent",
+ "setspent",
+ };
+
+_Static_assert ((array_length (nss_function_name_array) * sizeof (void *))
+ == sizeof (struct nss_module_functions),
+ "length of nss_module_name_array");
+_Static_assert (array_length (nss_function_name_array)
+ == array_length ((struct nss_module) { 0 }.functions.untyped),
+ "length of nss_module_name_array");
+
+static bool
+module_load (struct nss_module *module)
+{
+ void *handle;
+ {
+ char *shlib_name;
+ if (__asprintf (&shlib_name, "libnss_%s.so%s",
+ module->name, __nss_shlib_revision) < 0)
+ /* This is definitely a temporary failure. Do not update
+ module->state. This will trigger another attempt at the next
+ call. */
+ return false;
+
+ handle = __libc_dlopen (shlib_name);
+ free (shlib_name);
+ }
+
+ if (handle == NULL)
+ {
+ /* dlopen failure. We do not know if this a temporary or
+ permanent error. See bug 22041. Update the state using the
+ double-checked locking idiom. */
+
+ __libc_lock_lock (nss_module_list_lock);
+ bool result = result;
+ switch ((enum nss_module_state) atomic_load_acquire (&module->state))
+ {
+ case nss_module_uninitialized:
+ atomic_store_release (&module->state, nss_module_failed);
+ result = false;
+ break;
+ case nss_module_loaded:
+ result = true;
+ break;
+ case nss_module_failed:
+ result = false;
+ break;
+ }
+ __libc_lock_unlock (nss_module_list_lock);
+ return result;
+ }
+
+ nss_module_functions_untyped pointers;
+
+ for (size_t idx = 0; idx < array_length (nss_function_name_array); ++idx)
+ {
+ char *function_name;
+ if (__asprintf (&function_name, "_nss_%s_%s",
+ module->name, nss_function_name_array[idx]) < 0)
+ {
+ /* Definitely a temporary error. */
+ __libc_dlclose (handle);
+ return false;
+ }
+ pointers[idx] = __libc_dlsym (handle, function_name);
+ free (function_name);
+#ifdef PTR_MANGLE
+ PTR_MANGLE (pointers[idx]);
+#endif
+ }
+
+ /* Intall the function pointers, following the double-checked
+ locking idiom. Delay this after all processing, in case loading
+ the module triggers unwinding. */
+ __libc_lock_lock (nss_module_list_lock);
+ switch ((enum nss_module_state) atomic_load_acquire (&module->state))
+ {
+ case nss_module_uninitialized:
+ case nss_module_failed:
+ memcpy (module->functions.untyped, pointers,
+ sizeof (module->functions.untyped));
+ module->handle = handle;
+ atomic_store_release (&module->state, nss_module_loaded);
+ break;
+ case nss_module_loaded:
+ /* This does not actually unload the module, only the reference
+ counter is decremented. */
+ __libc_dlclose (handle);
+ break;
+ }
+ __libc_lock_unlock (nss_module_list_lock);
+ return true;
+}
+
+/* Ensures that MODULE is in a loaded or failed state. */
+bool
+__nss_module_load (struct nss_module *module)
+{
+ switch ((enum nss_module_state) atomic_load_acquire (&module->state))
+ {
+ case nss_module_uninitialized:
+ return module_load (module);
+ case nss_module_loaded:
+ /* Loading has already succeeded. */
+ return true;
+ case nss_module_failed:
+ /* Loading previously failed. */
+ return false;
+ }
+ __builtin_unreachable ();
+}
+
+static int
+name_search (const void *left, const void *right)
+{
+ return strcmp (left, right);
+}
+
+void *
+__nss_module_get_function (struct nss_module *module, const char *name)
+{
+ if (!__nss_module_load (module))
+ return NULL;
+
+ function_name *name_entry = bsearch (name, nss_function_name_array,
+ array_length (nss_function_name_array),
+ sizeof (function_name), name_search);
+ assert (name_entry != NULL);
+ size_t idx = name_entry - nss_function_name_array;
+ void *fptr = module->functions.untyped[idx];
+#ifdef PTR_DEMANGLE
+ PTR_DEMANGLE (fptr);
+#endif
+ return fptr;
+}
+
+void __libc_freeres_fn_section
+__nss_module_freeres (void)
+{
+ struct nss_module *current = nss_module_list;
+ while (current != NULL)
+ {
+ if (current->state == nss_module_loaded)
+ __libc_dlclose (current->handle);
+
+ struct nss_module *next = current->next;
+ free (current);
+ current = next;
+ }
+ nss_module_list = NULL;
+}
diff --git a/nss/nss_module.h b/nss/nss_module.h
new file mode 100644
index 0000000000..745f99a58e
--- /dev/null
+++ b/nss/nss_module.h
@@ -0,0 +1,152 @@
+/* Global list of NSS service modules.
+ Copyright (c) 2020 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
+ <https://www.gnu.org/licenses/>. */
+
+#ifndef _NSS_MODULE_H
+#define _NSS_MODULE_H
+
+#include <nss.h>
+#include <stdbool.h>
+
+/* Typed function pointers for all functions that can be defined by a
+ service module. */
+struct nss_module_functions
+{
+ nss_endaliasent *endaliasent;
+ nss_endetherent *endetherent;
+ nss_endgrent *endgrent;
+ nss_endhostent *endhostent;
+ nss_endnetent *endnetent;
+ nss_endnetgrent *endnetgrent;
+ nss_endprotoent *endprotoent;
+ nss_endpwent *endpwent;
+ nss_endrpcent *endrpcent;
+ nss_endservent *endservent;
+ nss_endsgent *endsgent;
+ nss_endspent *endspent;
+ nss_getaliasbyname_r *getaliasbyname_r;
+ nss_getaliasent_r *getaliasent_r;
+ nss_getcanonname_r *getcanonname_r;
+ nss_getetherent_r *getetherent_r;
+ nss_getgrent_r *getgrent_r;
+ nss_getgrgid_r *getgrgid_r;
+ nss_getgrnam_r *getgrnam_r;
+ nss_gethostbyaddr2_r *gethostbyaddr2_r;
+ nss_gethostbyaddr_r *gethostbyaddr_r;
+ nss_gethostbyname2_r *gethostbyname2_r;
+ nss_gethostbyname3_r *gethostbyname3_r;
+ nss_gethostbyname4_r *gethostbyname4_r;
+ nss_gethostbyname_r *gethostbyname_r;
+ nss_gethostent_r *gethostent_r;
+ nss_gethostton_r *gethostton_r;
+ nss_getnetbyaddr_r *getnetbyaddr_r;
+ nss_getnetbyname_r *getnetbyname_r;
+ nss_getnetent_r *getnetent_r;
+ nss_getnetgrent_r *getnetgrent_r;
+ nss_getntohost_r *getntohost_r;
+ nss_getprotobyname_r *getprotobyname_r;
+ nss_getprotobynumber_r *getprotobynumber_r;
+ nss_getprotoent_r *getprotoent_r;
+ nss_getpublickey *getpublickey;
+ nss_getpwent_r *getpwent_r;
+ nss_getpwnam_r *getpwnam_r;
+ nss_getpwuid_r *getpwuid_r;
+ nss_getrpcbyname_r *getrpcbyname_r;
+ nss_getrpcbynumber_r *getrpcbynumber_r;
+ nss_getrpcent_r *getrpcent_r;
+ nss_getsecretkey *getsecretkey;
+ nss_getservbyname_r *getservbyname_r;
+ nss_getservbyport_r *getservbyport_r;
+ nss_getservent_r *getservent_r;
+ nss_getsgent_r *getsgent_r;
+ nss_getsgnam_r *getsgnam_r;
+ nss_getspent_r *getspent_r;
+ nss_getspnam_r *getspnam_r;
+ nss_initgroups_dyn *initgroups_dyn;
+ nss_netname2user *netname2user;
+ nss_setaliasent *setaliasent;
+ nss_setetherent *setetherent;
+ nss_setgrent *setgrent;
+ nss_sethostent *sethostent;
+ nss_setnetent *setnetent;
+ nss_setnetgrent *setnetgrent;
+ nss_setprotoent *setprotoent;
+ nss_setpwent *setpwent;
+ nss_setrpcent *setrpcent;
+ nss_setservent *setservent;
+ nss_setsgent *setsgent;
+ nss_setspent *setspent;
+};
+
+/* Untyped version of struct nss_module_functions, for consistent
+ processing purposes. */
+typedef void *nss_module_functions_untyped[sizeof (struct nss_module_functions)
+ / sizeof (void *)];
+
+/* Initialization state of a NSS module. */
+enum nss_module_state
+{
+ nss_module_uninitialized,
+ nss_module_loaded,
+ nss_module_failed,
+};
+
+/* A NSS service module (potentially unloaded). Client code should
+ use the functions below. */
+struct nss_module
+{
+ /* Actual type is enum nss_module_state. Use int due to atomic
+ access. Used in a double-checked locking idiom. */
+ int state;
+
+ /* The function pointers in the module. */
+ union
+ {
+ struct nss_module_functions typed;
+ nss_module_functions_untyped untyped;
+ } functions;
+
+ /* Only used for __libc_freeres unloading. */
+ void *handle;
+
+ /* The next module in the list. */
+ struct nss_module *next;
+
+ /* The name of the module (as it appears in /etc/nsswitch.conf). */
+ char name[];
+};
+
+/* Allocates the NSS module NAME (of NAME_LENGTH bytes) and places it
+ into the global list. If it already exists in the list, return the
+ pre-existing module. This does not actually load the module.
+ Returns NULL on memory allocation failure. */
+struct nss_module *__nss_module_allocate (const char *name,
+ size_t name_length) attribute_hidden;
+
+/* Ensures that MODULE is in a loaded or failed state. */
+bool __nss_module_load (struct nss_module *module) attribute_hidden;
+
+/* Ensures that MODULE is loaded and returns a pointer to the function
+ NAME defined in it. Returns NULL if MODULE could not be loaded, or
+ if the function NAME is not defined in the module. */
+void *__nss_module_get_function (struct nss_module *module, const char *name)
+ attribute_hidden;
+
+/* Called from __libc_freeres. */
+void __nss_module_freeres (void) attribute_hidden;
+
+#endif /* NSS_MODULE_H */
--
2.21.1
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