[PATCH] sched: fix fork() error path to not crash.

[PATCH] sched: fix fork() error path to not crash.

[Salman Qazi]

In dup_task_struct, if arch_dup_task_struct fails, the clean up
code fails to clean up correctly.  That's because the clean up
code depends on unininitalized ti->task pointer.  We fix this
by making sure that the task and thread_info know about each other
before we attempt to take the error path.

Signed-off-by: Salman Qazi <sqazi@google.com>
---
 kernel/fork.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index ab5211b..f00e319 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -304,12 +304,17 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
 	}
 
 	err = arch_dup_task_struct(tsk, orig);
-	if (err)
-		goto out;
 
+	/*
+	 * We defer looking at err, because we will need this setup
+	 * for the clean up path to work correctly.
+	 */
 	tsk->stack = ti;
-
 	setup_thread_stack(tsk, orig);
+
+	if (err)
+		goto out;
+
 	clear_user_return_notifier(tsk);
 	clear_tsk_need_resched(tsk);
 	stackend = end_of_stack(tsk);

Re: [PATCH] sched: fix fork() error path to not crash.

[Peter Zijlstra]

On Mon, 2012-06-25 at 18:18 -0700, Salman Qazi wrote:
> In dup_task_struct, if arch_dup_task_struct fails, the clean up
> code fails to clean up correctly.  That's because the clean up
> code depends on unininitalized ti->task pointer.  We fix this
> by making sure that the task and thread_info know about each other
> before we attempt to take the error path.
> 
> Signed-off-by: Salman Qazi <sqazi@google.com>

Cute, however did you find that?

Re: [PATCH] sched: fix fork() error path to not crash.

[Salman Qazi]

On Tue, Jun 26, 2012 at 1:40 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Mon, 2012-06-25 at 18:18 -0700, Salman Qazi wrote:
>> In dup_task_struct, if arch_dup_task_struct fails, the clean up
>> code fails to clean up correctly.  That's because the clean up
>> code depends on unininitalized ti->task pointer.  We fix this
>> by making sure that the task and thread_info know about each other
>> before we attempt to take the error path.
>>
>> Signed-off-by: Salman Qazi <sqazi@google.com>
>
> Cute, however did you find that?

Our test infrastructure folks have developed a fault injection
framework geared towards detecting bugs triggered by memory allocation
failures in random places.

[tip:sched/core] sched: Fix fork() error path to not crash

[tip-bot for Salman Qazi]

Commit-ID:  164c33c6adee609b8b9062cce4c10f764d0dce13
Gitweb:     http://git.kernel.org/tip/164c33c6adee609b8b9062cce4c10f764d0dce13
Author:     Salman Qazi <sqazi@google.com>
AuthorDate: Mon, 25 Jun 2012 18:18:15 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 Jul 2012 20:57:32 +0200

sched: Fix fork() error path to not crash

In dup_task_struct(), if arch_dup_task_struct() fails, the clean up
code fails to clean up correctly.  That's because the clean up
code depends on unininitalized ti->task pointer.  We fix this
by making sure that the task and thread_info know about each other
before we attempt to take the error path.

Signed-off-by: Salman Qazi <sqazi@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120626011815.11323.5533.stgit@dungbeetle.mtv.corp.google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/fork.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index ab5211b..f00e319 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -304,12 +304,17 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
 	}
 
 	err = arch_dup_task_struct(tsk, orig);
-	if (err)
-		goto out;
 
+	/*
+	 * We defer looking at err, because we will need this setup
+	 * for the clean up path to work correctly.
+	 */
 	tsk->stack = ti;
-
 	setup_thread_stack(tsk, orig);
+
+	if (err)
+		goto out;
+
 	clear_user_return_notifier(tsk);
 	clear_tsk_need_resched(tsk);
 	stackend = end_of_stack(tsk);