From 30add3e6b3e3211b3e2d4a093f45bee5c6e24b8b Mon Sep 17 00:00:00 2001 From: Corinna Vinschen Date: Thu, 1 Dec 2022 21:33:14 +0100 Subject: [PATCH] Cygwin: exec: don't access cygheap before it's initialized This is a long-standing thinko. When you exec a process, dll_crt0_0 in the child process calls child_info_spawn::handle_spawn(). handle_spawn() initialises the cygheap. Now consider calling strace. Strace is a non-Cygwin process dynamically loading cygwin1.dll via LoadLibrary. This in turn initializes the DLL: - dll_crt0_0 finds that the process it attaches to has been exec'd, so child_info_spawn::handle_spawn() is called. - If the DLL is being dynamically loaded, handle_spawn() calls child_info_spawn::get_parent_handle(). This in turn tries to set the moreinfo->myself_pinfo value inside the cygheap to NULL. - However, at this time, the cygheap has not yet been initialized. This only occurs in the cygheap_fixup_in_child() call after get_parent_handle() returns. --> SEGV This thinko never had a negative side effect, because the cygheap was pre-allocated at DLL load time until commit 2f9b8ff00cce ("Cygwin: decouple cygheap from Cygwin DLL"). With 2f9b8ff00cce, the cygheap actually doesn't exist until after the call to cygheap_fixup_in_child(). Fix this problem by moving the assignment after the call to cygheap_fixup_in_child(). Fixes: 3de7be4c1deb ("* DevNotes: Add entry cgf-000007. [...]") Fixes: 2f9b8ff00cce ("Cygwin: decouple cygheap from Cygwin DLL") Signed-off-by: Corinna Vinschen --- winsup/cygwin/dcrt0.cc | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc index e5f19f1f9..5c5a280cc 100644 --- a/winsup/cygwin/dcrt0.cc +++ b/winsup/cygwin/dcrt0.cc @@ -620,7 +620,6 @@ bool child_info_spawn::get_parent_handle () { parent = OpenProcess (PROCESS_VM_READ, FALSE, parent_winpid); - moreinfo->myself_pinfo = NULL; return !!parent; } @@ -632,6 +631,8 @@ child_info_spawn::handle_spawn () if (!dynamically_loaded || get_parent_handle ()) { cygheap_fixup_in_child (true); + if (dynamically_loaded) + moreinfo->myself_pinfo = NULL; memory_init (); }