afea16b8f7
The remainder of the patch series proposed by upstream [2] for the locking synchronization issue [1]. [1] https://www.openwall.com/lists/musl/2020/05/22/3 [2] https://www.openwall.com/lists/musl/2020/05/22/10 Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
52 lines
2.1 KiB
Diff
52 lines
2.1 KiB
Diff
From 4d5aa20a94a2d3fae3e69289dc23ecafbd0c16c4 Mon Sep 17 00:00:00 2001
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From: Rich Felker <dalias@aerifal.cx>
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Date: Fri, 22 May 2020 17:35:14 -0400
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Subject: [PATCH 1/4] reorder thread list unlink in pthread_exit after all
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locks
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since the backend for LOCK() skips locking if single-threaded, it's
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unsafe to make the process appear single-threaded before the last use
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of lock.
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this fixes potential unsynchronized access to a linked list via
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__dl_thread_cleanup.
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---
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src/thread/pthread_create.c | 19 +++++++++++--------
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1 file changed, 11 insertions(+), 8 deletions(-)
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--- a/src/thread/pthread_create.c
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+++ b/src/thread/pthread_create.c
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@@ -90,14 +90,7 @@ _Noreturn void __pthread_exit(void *resu
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exit(0);
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}
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- /* At this point we are committed to thread termination. Unlink
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- * the thread from the list. This change will not be visible
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- * until the lock is released, which only happens after SYS_exit
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- * has been called, via the exit futex address pointing at the lock. */
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- libc.threads_minus_1--;
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- self->next->prev = self->prev;
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- self->prev->next = self->next;
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- self->prev = self->next = self;
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+ /* At this point we are committed to thread termination. */
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/* Process robust list in userspace to handle non-pshared mutexes
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* and the detached thread case where the robust list head will
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@@ -121,6 +114,16 @@ _Noreturn void __pthread_exit(void *resu
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__do_orphaned_stdio_locks();
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__dl_thread_cleanup();
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+ /* Last, unlink thread from the list. This change will not be visible
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+ * until the lock is released, which only happens after SYS_exit
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+ * has been called, via the exit futex address pointing at the lock.
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+ * This needs to happen after any possible calls to LOCK() that might
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+ * skip locking if libc.threads_minus_1 is zero. */
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+ libc.threads_minus_1--;
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+ self->next->prev = self->prev;
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+ self->prev->next = self->next;
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+ self->prev = self->next = self;
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+
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/* This atomic potentially competes with a concurrent pthread_detach
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* call; the loser is responsible for freeing thread resources. */
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int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING);
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