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Avoid race in nscd 

2012-05-15  Jeff Law  <law@redhat.com>
            Andreas Jaeger  <aj@suse.de>

        [BZ #13594]
        * nscd/nscd-client.h (__nscd_acquire_maplock): New function, split
        out from...
        * nscd/nscd_helper.c (__nscd_get_map_ref): ... here.
        * nscd/nscd-client.h: Add __nscd_acquire_maplock.
        * nscd/nscd_gethst_r.c (__nscd_get_nl_timestamp): Add locking to
        code changing __hst_map_handle.map.
This commit is contained in:
Andreas Jaeger 2012-05-15 20:35:53 +02:00
parent ba75122dd9
commit 509072a0f7
5 changed files with 60 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
ChangeLog
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@ -1,3 +1,14 @@
2012-05-15 Jeff Law <law@redhat.com>
Andreas Jaeger <aj@suse.de>
[BZ #13594]
* nscd/nscd-client.h (__nscd_acquire_maplock): New function, split
out from...
* nscd/nscd_helper.c (__nscd_get_map_ref): ... here.
* nscd/nscd-client.h: Add __nscd_acquire_maplock.
* nscd/nscd_gethst_r.c (__nscd_get_nl_timestamp): Add locking to
code changing __hst_map_handle.map.
2012-05-15 Roland McGrath <roland@hack.frob.com>
* configure.in (sysnames): Look for Implies-before and Implies-after

20
NEWS
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@ -18,16 +18,16 @@ Version 2.16
11494, 11521, 11677, 11837, 11959, 12047, 12097, 12193, 12297, 12298,
12301, 12340, 12354, 13058, 13361, 13525, 13526, 13527, 13528, 13529,
13530, 13531, 13532, 13533, 13547, 13551, 13552, 13553, 13555, 13556,
13559, 13563, 13566, 13583, 13592, 13613, 13618, 13637, 13656, 13658,
13673, 13691, 13695, 13704, 13705, 13706, 13726, 13738, 13739, 13750,
13758, 13760, 13761, 13775, 13786, 13787, 13792, 13806, 13824, 13840,
13841, 13844, 13846, 13851, 13852, 13854, 13871, 13872, 13873, 13879,
13883, 13884, 13885, 13886, 13892, 13895, 13908, 13910, 13911, 13912,
13913, 13914, 13915, 13916, 13917, 13918, 13919, 13920, 13921, 13922,
13923, 13924, 13926, 13927, 13928, 13938, 13941, 13942, 13954, 13955,
13956, 13963, 13967, 13970, 13973, 13979, 13983, 13986, 14012, 14027,
14033, 14034, 14040, 14043, 14044, 14049, 14053, 14055, 14064, 14080,
14083, 14103, 14104
13559, 13563, 13566, 13583, 13592, 13594, 13613, 13618, 13637, 13656,
13658, 13673, 13691, 13695, 13704, 13705, 13706, 13726, 13738, 13739,
13750, 13758, 13760, 13761, 13775, 13786, 13787, 13792, 13806, 13824,
13840, 13841, 13844, 13846, 13851, 13852, 13854, 13871, 13872, 13873,
13879, 13883, 13884, 13885, 13886, 13892, 13895, 13908, 13910, 13911,
13912, 13913, 13914, 13915, 13916, 13917, 13918, 13919, 13920, 13921,
13922, 13923, 13924, 13926, 13927, 13928, 13938, 13941, 13942, 13954,
13955, 13956, 13963, 13967, 13970, 13973, 13979, 13983, 13986, 14012,
14027, 14033, 14034, 14040, 14043, 14044, 14049, 14053, 14055, 14064,
14080, 14083, 14103, 14104
* ISO C11 support:

21
nscd/nscd-client.h
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@ -1,5 +1,4 @@
/* Copyright (c) 1998, 1999, 2000, 2003, 2004, 2005, 2006, 2007, 2009, 2011
Free Software Foundation, Inc.
/* Copyright (c) 1998-2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Thorsten Kukuk <kukuk@suse.de>, 1998.
@ -322,6 +321,24 @@ struct locked_map_ptr
};
#define libc_locked_map_ptr(class, name) class struct locked_map_ptr name
/* Try acquiring lock for mapptr, returns true if it succeeds, false
if not. */
static inline bool __nscd_acquire_maplock (volatile struct locked_map_ptr *mapptr)
{
int cnt = 0;
while (__builtin_expect (atomic_compare_and_exchange_val_acq (&mapptr->lock,
1, 0) != 0, 0))
{
// XXX Best number of rounds?
if (__builtin_expect (++cnt > 5, 0))
return false;
atomic_delay ();
}
return true;
}
/* Open socket connection to nscd server. */
extern int __nscd_open_socket (const char *key, size_t keylen,

21
nscd/nscd_gethst_r.c
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@ -1,5 +1,4 @@
/* Copyright (C) 1998-2005, 2006, 2007, 2008, 2009, 2011
Free Software Foundation, Inc.
/* Copyright (C) 1998-2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
@ -100,9 +99,18 @@ libc_freeres_fn (hst_map_free)
uint32_t
__nscd_get_nl_timestamp (void)
{
uint32_t retval;
if (__nss_not_use_nscd_hosts != 0)
return 0;
/* __nscd_get_mapping can change hst_map_handle.mapped to NO_MAPPING.
However, __nscd_get_mapping assumes the prior value was not NO_MAPPING.
Thus we have to acquire the lock to prevent this thread from changing
hst_map_handle.mapped to NO_MAPPING while another thread is inside
__nscd_get_mapping. */
if (!__nscd_acquire_maplock (&__hst_map_handle))
return 0;
struct mapped_database *map = __hst_map_handle.mapped;
if (map == NULL
@ -112,9 +120,14 @@ __nscd_get_nl_timestamp (void)
map = __nscd_get_mapping (GETFDHST, "hosts", &__hst_map_handle.mapped);
if (map == NO_MAPPING)
return 0;
retval = 0;
else
retval = map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
return map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
/* Release the lock. */
__hst_map_handle.lock = 0;
return retval;
}

15
nscd/nscd_helper.c
View File

@ -1,4 +1,4 @@
/* Copyright (C) 1998-2007, 2008, 2009 Free Software Foundation, Inc.
/* Copyright (C) 1998-2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
@ -419,7 +419,6 @@ __nscd_get_mapping (request_type type, const char *key,
return result;
}
struct mapped_database *
__nscd_get_map_ref (request_type type, const char *name,
volatile struct locked_map_ptr *mapptr, int *gc_cyclep)
@ -428,16 +427,8 @@ __nscd_get_map_ref (request_type type, const char *name,
if (cur == NO_MAPPING)
return cur;
int cnt = 0;
while (__builtin_expect (atomic_compare_and_exchange_val_acq (&mapptr->lock,
1, 0) != 0, 0))
{
// XXX Best number of rounds?
if (__builtin_expect (++cnt > 5, 0))
return NO_MAPPING;
atomic_delay ();
}
if (!__nscd_acquire_maplock (mapptr))
return NO_MAPPING;
cur = mapptr->mapped;