138 lines
4.2 KiB
Diff
138 lines
4.2 KiB
Diff
commit 509072a0f7f8a37bedf61a78c0cdd7783368c65a
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Author: Andreas Jaeger <aj@suse.de>
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Date: Tue May 15 20:35:53 2012 +0200
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Avoid race in nscd
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2012-05-15 Jeff Law <law@redhat.com>
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Andreas Jaeger <aj@suse.de>
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[BZ #13594]
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* nscd/nscd-client.h (__nscd_acquire_maplock): New function, split
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out from...
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* nscd/nscd_helper.c (__nscd_get_map_ref): ... here.
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* nscd/nscd-client.h: Add __nscd_acquire_maplock.
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* nscd/nscd_gethst_r.c (__nscd_get_nl_timestamp): Add locking to
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code changing __hst_map_handle.map.
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diff --git a/nscd/nscd-client.h b/nscd/nscd-client.h
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index e57a23c..325368e 100644
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--- a/nscd/nscd-client.h
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+++ b/nscd/nscd-client.h
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@@ -1,5 +1,4 @@
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-/* Copyright (c) 1998, 1999, 2000, 2003, 2004, 2005, 2006, 2007, 2009, 2011
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- Free Software Foundation, Inc.
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+/* Copyright (c) 1998-2012 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Thorsten Kukuk <kukuk@suse.de>, 1998.
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@@ -322,6 +321,24 @@ struct locked_map_ptr
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};
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#define libc_locked_map_ptr(class, name) class struct locked_map_ptr name
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+/* Try acquiring lock for mapptr, returns true if it succeeds, false
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+ if not. */
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+static inline bool __nscd_acquire_maplock (volatile struct locked_map_ptr *mapptr)
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+{
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+ int cnt = 0;
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+ while (__builtin_expect (atomic_compare_and_exchange_val_acq (&mapptr->lock,
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+ 1, 0) != 0, 0))
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+ {
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+ // XXX Best number of rounds?
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+ if (__builtin_expect (++cnt > 5, 0))
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+ return false;
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+
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+ atomic_delay ();
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+ }
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+
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+ return true;
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+}
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+
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/* Open socket connection to nscd server. */
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extern int __nscd_open_socket (const char *key, size_t keylen,
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diff --git a/nscd/nscd_gethst_r.c b/nscd/nscd_gethst_r.c
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index c1661f8..d64ad2e 100644
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--- a/nscd/nscd_gethst_r.c
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+++ b/nscd/nscd_gethst_r.c
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@@ -1,5 +1,4 @@
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-/* Copyright (C) 1998-2005, 2006, 2007, 2008, 2009, 2011
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- Free Software Foundation, Inc.
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+/* Copyright (C) 1998-2012 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
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@@ -100,9 +99,18 @@ libc_freeres_fn (hst_map_free)
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uint32_t
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__nscd_get_nl_timestamp (void)
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{
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+ uint32_t retval;
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if (__nss_not_use_nscd_hosts != 0)
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return 0;
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+ /* __nscd_get_mapping can change hst_map_handle.mapped to NO_MAPPING.
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+ However, __nscd_get_mapping assumes the prior value was not NO_MAPPING.
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+ Thus we have to acquire the lock to prevent this thread from changing
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+ hst_map_handle.mapped to NO_MAPPING while another thread is inside
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+ __nscd_get_mapping. */
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+ if (!__nscd_acquire_maplock (&__hst_map_handle))
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+ return 0;
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+
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struct mapped_database *map = __hst_map_handle.mapped;
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if (map == NULL
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@@ -112,9 +120,14 @@ __nscd_get_nl_timestamp (void)
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map = __nscd_get_mapping (GETFDHST, "hosts", &__hst_map_handle.mapped);
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if (map == NO_MAPPING)
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- return 0;
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+ retval = 0;
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+ else
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+ retval = map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
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+
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+ /* Release the lock. */
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+ __hst_map_handle.lock = 0;
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- return map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
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+ return retval;
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}
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diff --git a/nscd/nscd_helper.c b/nscd/nscd_helper.c
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index 92558b6..96fb93d 100644
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--- a/nscd/nscd_helper.c
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+++ b/nscd/nscd_helper.c
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@@ -1,4 +1,4 @@
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-/* Copyright (C) 1998-2007, 2008, 2009 Free Software Foundation, Inc.
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+/* Copyright (C) 1998-2012 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
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@@ -419,7 +419,6 @@ __nscd_get_mapping (request_type type, const char *key,
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return result;
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}
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-
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struct mapped_database *
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__nscd_get_map_ref (request_type type, const char *name,
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volatile struct locked_map_ptr *mapptr, int *gc_cyclep)
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@@ -428,16 +427,8 @@ __nscd_get_map_ref (request_type type, const char *name,
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if (cur == NO_MAPPING)
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return cur;
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- int cnt = 0;
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- while (__builtin_expect (atomic_compare_and_exchange_val_acq (&mapptr->lock,
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- 1, 0) != 0, 0))
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- {
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- // XXX Best number of rounds?
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- if (__builtin_expect (++cnt > 5, 0))
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- return NO_MAPPING;
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-
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- atomic_delay ();
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- }
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+ if (!__nscd_acquire_maplock (mapptr))
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+ return NO_MAPPING;
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cur = mapptr->mapped;
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