From f1671f6d783a2385d32e11f456cbe32f0e4b4b49 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
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 <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
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);
}
--
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