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commit 8e31cafb268938729a1314806a924d73fb1991c5
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Author: Torvald Riegel <triegel@redhat.com>
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Date: Wed Dec 21 13:37:19 2016 +0100
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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
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acquired by the forked child process. We have to clear the list of
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acquired robust mutexes before registering this list with the kernel;
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otherwise, if some of the robust mutexes are process-shared, the parent
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process can alter the child's robust mutex list, which can lead to
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deadlocks or even modification of memory that may not be occupied by a
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mutex anymore.
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[BZ #19402]
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* sysdeps/nptl/fork.c (__libc_fork): Clear list of acquired robust
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mutexes.
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Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/fork.c
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===================================================================
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--- glibc-2.17-c758a686.orig/nptl/sysdeps/unix/sysv/linux/fork.c
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+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/fork.c
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@@ -161,12 +161,20 @@ __libc_fork (void)
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#endif
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#ifdef __NR_set_robust_list
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- /* Initialize the robust mutex list which has been reset during
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- the fork. We do not check for errors since if it fails here
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- it failed at process start as well and noone could have used
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- robust mutexes. We also do not have to set
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- self->robust_head.futex_offset since we inherit the correct
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- value from the parent. */
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+ /* Initialize the robust mutex list setting in the kernel which has
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+ been reset during the fork. We do not check for errors because if
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+ it fails here, it must have failed at process startup as well and
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+ nobody could have used robust mutexes.
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+ Before we do that, we have to clear the list of robust mutexes
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+ because we do not inherit ownership of mutexes from the parent.
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+ We do not have to set self->robust_head.futex_offset since we do
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+ inherit the correct value from the parent. We do not need to clear
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+ the pending operation because it must have been zero when fork was
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+ called. */
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+# ifdef __PTHREAD_MUTEX_HAVE_PREV
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+ self->robust_prev = &self->robust_head;
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+# endif
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+ self->robust_head.list = &self->robust_head;
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# ifdef SHARED
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if (__builtin_expect (__libc_pthread_functions_init, 0))
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PTHFCT_CALL (ptr_set_robust, (self));
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