From cfc4f957ff7bffa6aaf7e4029ee9c8689b43c366 Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Mon, 18 Oct 2004 08:53:35 -0700 Subject: [PATCH] fix PTRACE_ATTACH race with real parent's wait calls There is a race between PTRACE_ATTACH and the real parent calling wait. For a moment, the task is put in PT_PTRACED but with its parent still pointing to its real_parent. In this circumstance, if the real parent calls wait without the WUNTRACED flag, he can see a stopped child status, which wait should never return without WUNTRACED when the caller is not using ptrace. Here it is not the caller that is using ptrace, but some third party. This patch avoids this race condition by adding the PT_ATTACHED flag to distinguish a real parent from a ptrace_attach parent when PT_PTRACED is set, and then having wait use this flag to confirm that things are in order and not consider the child ptraced when its ->ptrace flags are set but its parent links have not yet been switched. (ptrace_check_attach also uses it similarly to rule out a possible race with a bogus ptrace call by the real parent during ptrace_attach.) While looking into this, I noticed that every arch's sys_execve has: current->ptrace &= ~PT_DTRACE; with no locking at all. So, if an exec happens in a race with PTRACE_ATTACH, you could wind up with ->ptrace not having PT_PTRACED set because this store clobbered it. That will cause later BUG hits because the parent links indicate ptracedness but the flag is not set. The patch corrects all the places I found to use task_lock around diddling ->ptrace when it's possible to be racing with ptrace_attach. (The ptrace operation code itself doesn't have this issue because it already excludes anyone else being in ptrace_attach.) Signed-off-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/ptrace.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 53132cd80429..f18247125091 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -63,6 +63,7 @@ #define PT_TRACE_EXEC 0x00000080 #define PT_TRACE_VFORK_DONE 0x00000100 #define PT_TRACE_EXIT 0x00000200 +#define PT_ATTACHED 0x00000400 /* parent != real_parent */ #define PT_TRACE_MASK 0x000003f4 -- cgit v1.2.3