From f1671f6d783a2385d32e11f456cbe32f0e4b4b49 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 13 Apr 2009 14:40:03 -0700 Subject: [PATCH] ptrace: fix exit_ptrace() vs ptrace_traceme() race Pointed out by Roland. The bug was recently introduced by me in "forget_original_parent: split out the un-ptrace part", commit 39c626ae47c469abdfd30c6e42eff884931380d6. Since that patch we have a window after exit_ptrace() drops tasklist and before forget_original_parent() takes it again. In this window the child can do ptrace(PTRACE_TRACEME) and nobody can untrace this child after that. Change ptrace_traceme() to not attach to the exiting ->real_parent. We don't report the error in this case, we pretend we attach right before ->real_parent calls exit_ptrace() which should untrace us anyway. Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 64191fa09b7e..dfcd83ceee3b 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -604,10 +604,11 @@ repeat: ret = security_ptrace_traceme(current->parent); /* - * Set the ptrace bit in the process ptrace flags. - * Then link us on our parent's ptraced list. + * Check PF_EXITING to ensure ->real_parent has not passed + * exit_ptrace(). Otherwise we don't report the error but + * pretend ->real_parent untraces us right after return. */ - if (!ret) { + if (!ret && !(current->real_parent->flags & PF_EXITING)) { current->ptrace |= PT_PTRACED; __ptrace_link(current, current->real_parent); } -- 2.20.1