linux-kernel - [PATCH 1/2] coredump: ensure all coredumping tasks have

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Message-ID: <20150929155502.GA15109@redhat.com>
Date:	Tue, 29 Sep 2015 17:55:02 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Kyle Walker <kwalker@...hat.com>,
	Michal Hocko <mhocko@...nel.org>,
	Stanislav Kozina <skozina@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] coredump: ensure all coredumping tasks have

task_will_free_mem() is wrong in many ways, and in particular the
SIGNAL_GROUP_COREDUMP check is not reliable: a task can participate
in the coredumping without SIGNAL_GROUP_COREDUMP bit set.

change zap_threads() paths to always set SIGNAL_GROUP_COREDUMP even
if other CLONE_VM processes can't react to SIGKILL. Fortunately, at
least oom-kill case if fine; it kills all tasks sharing the same mm,
so it should also kill the process which actually dumps the core.

The change in prepare_signal() is not strictly necessary, it just
ensures that the patch does not bring another subtle behavioural
change. But it reminds us that this SIGNAL_GROUP_EXIT/COREDUMP case
needs more changes.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/coredump.c   | 12 ++++++------
 kernel/signal.c |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 53d7d46..4fed8d0 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -282,11 +282,13 @@ out:
 	return ispipe;
 }
 
-static int zap_process(struct task_struct *start, int exit_code)
+static int zap_process(struct task_struct *start, int exit_code, int flags)
 {
 	struct task_struct *t;
 	int nr = 0;
 
+	/* ignore all signals except SIGKILL, see prepare_signal() */
+	start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
 	start->signal->group_exit_code = exit_code;
 	start->signal->group_stop_count = 0;
 
@@ -313,10 +315,8 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 	spin_lock_irq(&tsk->sighand->siglock);
 	if (!signal_group_exit(tsk->signal)) {
 		mm->core_state = core_state;
-		nr = zap_process(tsk, exit_code);
 		tsk->signal->group_exit_task = tsk;
-		/* ignore all signals except SIGKILL, see prepare_signal() */
-		tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
+		nr = zap_process(tsk, exit_code, 0);
 		clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);
@@ -367,8 +367,8 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 			if (p->mm) {
 				if (unlikely(p->mm == mm)) {
 					lock_task_sighand(p, &flags);
-					nr += zap_process(p, exit_code);
-					p->signal->flags = SIGNAL_GROUP_EXIT;
+					nr += zap_process(p, exit_code,
+							  SIGNAL_GROUP_EXIT);
 					unlock_task_sighand(p, &flags);
 				}
 				break;
diff --git a/kernel/signal.c b/kernel/signal.c
index f2cbd4e..c0b01fe 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -788,7 +788,7 @@ static bool prepare_signal(int sig, struct task_struct *p, bool force)
 	sigset_t flush;
 
 	if (signal->flags & (SIGNAL_GROUP_EXIT | SIGNAL_GROUP_COREDUMP)) {
-		if (signal->flags & SIGNAL_GROUP_COREDUMP)
+		if (!(signal->flags & SIGNAL_GROUP_EXIT))
 			return sig == SIGKILL;
 		/*
 		 * The process is in the middle of dying, nothing to do.
-- 
2.4.3

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