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| author | Rich Felker <dalias@aerifal.cx> | 2019-03-01 22:47:29 -0500 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2019-03-03 12:06:44 -0500 |
| commit | 8e43b5613eea0b557a2e91368917a90f4b0e4ab2 (patch) | |
| tree | ba010ea02c324ef7363005e8def822fff6aaae09 /ldso | |
| parent | 188759bbee057aa94db2bbb7cf7f5855f3b9ab53 (diff) | |
| download | musl-8e43b5613eea0b557a2e91368917a90f4b0e4ab2.tar.gz | |
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.
Diffstat (limited to 'ldso')
| -rw-r--r-- | ldso/dynlink.c | 18 |
1 files changed, 17 insertions, 1 deletions
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<<DT_FINI_ARRAY)) { @@ -1431,7 +1443,7 @@ static void do_init_fini(struct dso **queue) pthread_mutex_lock(&init_fini_lock); for (i=0; (p=queue[i]); i++) { - while (p->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; |