If libthr.so is dlopened without RTLD_GLOBAL flag, the libthr symbols

do not participate in the global symbols namespace, but rtld locks are
still replaced and functions are interposed.  In particular,
__pthread_map_stacks_exec is resolved to the libc version.  If a
library is loaded later, which requires adjustment of the stack
protection mode, rtld calls into libc __pthread_map_stacks_exec due to
the symbols scope.  The libc version might recurse into binder and
recursively acquire rtld bind lock, causing the hang.

Make libc __pthread_map_stacks_exec() interposed, which synchronizes
rtld locks and version of the stack exec hook when libthr loaded,
regardless of the symbol scope control or symbol resolution order.

The __pthread_map_stacks_exec() symbol is removed from the private
version in libthr since libc symbol now operates correctly in presence
of libthr.

Reported and tested by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index 5caf9a3..554f3a2 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -224,6 +224,7 @@ enum {
 	INTERPOS_kevent,
 	INTERPOS_wait6,
 	INTERPOS_ppoll,
+	INTERPOS_map_stacks_exec,
 	INTERPOS_MAX
 };
 
@@ -381,6 +382,7 @@ int _elf_aux_info(int aux, void *buf, int buflen);
 struct dl_phdr_info;
 int __elf_phdr_match_addr(struct dl_phdr_info *, void *);
 void __init_elf_aux_vector(void);
+void __libc_map_stacks_exec();
 
 void	_pthread_cancel_enter(int);
 void	_pthread_cancel_leave(int);