From 8e43b5613eea0b557a2e91368917a90f4b0e4ab2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Fri, 1 Mar 2019 22:47:29 -0500 Subject: [PATCH] synchronize shared library dtor exec against concurrent loads/ctors previously, going way back, there was simply no synchronization here. a call to exit concurrent with ctor execution from dlopen could cause a dtor to execute concurrently with its corresponding ctor, or could cause dtors for newly-constructed libraries to be skipped. introduce a shutting_down state that blocks further ctor execution, producing the quiescence the dtor execution loop needs to ensure any kind of consistency, and that blocks further calls to dlopen so that a call into dlopen from a dtor cannot deadlock. better approaches to some of this may be possible, but the changes here at least make things safe. --- ldso/dynlink.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/ldso/dynlink.c b/ldso/dynlink.c index 777be489..20328285 100644 --- a/ldso/dynlink.c +++ b/ldso/dynlink.c @@ -124,6 +124,7 @@ static int runtime; static int ldd_mode; static int ldso_fail; static int noload; +static int shutting_down; static jmp_buf *rtld_fail; static pthread_rwlock_t lock; static struct debug debug; @@ -1350,7 +1351,18 @@ void __libc_exit_fini() { struct dso *p; size_t dyn[DYN_CNT]; + int self = __pthread_self()->tid; + + /* Take both locks before setting shutting_down, so that + * either lock is sufficient to read its value. The lock + * order matches that in dlopen to avoid deadlock. */ + pthread_rwlock_wrlock(&lock); + pthread_mutex_lock(&init_fini_lock); + shutting_down = 1; + pthread_rwlock_unlock(&lock); for (p=fini_head; p; p=p->fini_next) { + while (p->ctor_visitor && p->ctor_visitor!=self) + pthread_cond_wait(&ctor_cond, &init_fini_lock); if (!p->constructed) continue; decode_vec(p->dynv, dyn, DYN_CNT); if (dyn[0] & (1<ctor_visitor && p->ctor_visitor!=self) + while ((p->ctor_visitor && p->ctor_visitor!=self) || shutting_down) pthread_cond_wait(&ctor_cond, &init_fini_lock); if (p->ctor_visitor || p->constructed) continue; @@ -1937,6 +1949,10 @@ void *dlopen(const char *file, int mode) __inhibit_ptc(); p = 0; + if (shutting_down) { + error("Cannot dlopen while program is exiting."); + goto end; + } orig_tls_tail = tls_tail; orig_tls_cnt = tls_cnt; orig_tls_offset = tls_offset;