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Clear list of acquired robust mutexes in the child process after forking.

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Robust mutexes acquired at the time of a call to fork() do not remain
acquired by the forked child process.  We have to clear the list of
acquired robust mutexes before registering this list with the kernel;
otherwise, if some of the robust mutexes are process-shared, the parent
process can alter the child's robust mutex list, which can lead to
deadlocks or even modification of memory that may not be occupied by a
mutex anymore.

	[BZ #19402]
	* sysdeps/nptl/fork.c (__libc_fork): Clear list of acquired robust
	mutexes.
This commit is contained in:
Torvald Riegel 2016-12-21 13:37:19 +01:00
parent 65810f0ef0
commit 8e31cafb26
2 changed files with 20 additions and 6 deletions
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@ -1,3 +1,9 @@
2016-01-13 Torvald Riegel <triegel@redhat.com>
[BZ #19402]
* sysdeps/nptl/fork.c (__libc_fork): Clear list of acquired robust
mutexes.
2016-01-13 Torvald Riegel <triegel@redhat.com>
[BZ #20985]

20
sysdeps/nptl/fork.c
View File

@ -162,12 +162,20 @@ __libc_fork (void)
#endif
#ifdef __NR_set_robust_list
/* Initialize the robust mutex list which has been reset during
the fork. We do not check for errors since if it fails here
it failed at process start as well and noone could have used
robust mutexes. We also do not have to set
self->robust_head.futex_offset since we inherit the correct
value from the parent. */
/* Initialize the robust mutex list setting in the kernel which has
been reset during the fork. We do not check for errors because if
it fails here, it must have failed at process startup as well and
nobody could have used robust mutexes.
Before we do that, we have to clear the list of robust mutexes
because we do not inherit ownership of mutexes from the parent.
We do not have to set self->robust_head.futex_offset since we do
inherit the correct value from the parent. We do not need to clear
the pending operation because it must have been zero when fork was
called. */
# ifdef __PTHREAD_MUTEX_HAVE_PREV
self->robust_prev = &self->robust_head;
# endif
self->robust_head.list = &self->robust_head;
# ifdef SHARED
if (__builtin_expect (__libc_pthread_functions_init, 0))
PTHFCT_CALL (ptr_set_robust, (self));