From: bsegall@google.com
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Roland McGrath <roland@hack.frob.com>,
Andrew Morton <akpm@linux-foundation.org>,
Tejun Heo <tj@kernel.org>
Subject: [PATCHv2] ptrace: fix PTRACE_LISTEN race corrupting task->state
Date: Tue, 04 Apr 2017 14:47:34 -0700
Message-ID: <xm26y3vfhmkp.fsf_-_@bsegall-linux.mtv.corp.google.com> (raw)
In-Reply-To: <20170224163611.GA24902@redhat.com> (Oleg Nesterov's message of "Fri, 24 Feb 2017 17:36:11 +0100")
In PT_SEIZED + LISTEN mode STOP/CONT signals cause a wakeup against
__TASK_TRACED. If this races with the ptrace_unfreeze_traced at the end
of a PTRACE_LISTEN, this can wake the task /after/ the check against
__TASK_TRACED, but before the reset of state to TASK_TRACED. This causes
it to instead clobber TASK_WAKING, allowing a subsequent wakeup against
TRACED while the task is still on the rq wake_list, corrupting it.
Signed-off-by: Ben Segall <bsegall@google.com>
---
v2: slight clarification in comments, put the conditional around the
whole wakeup area
Oleg mentioned a preference for making LISTEN unfreeze instead; I have
no preference there, just wanted to make sure that this doesn't get
forgotten entirely.
kernel/ptrace.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0af928712174..7cc49c3e73af 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -184,11 +184,17 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
WARN_ON(!task->ptrace || task->parent != current);
+ /*
+ * PTRACE_LISTEN can allow ptrace_trap_notify to wake us up
+ * remotely. Recheck state under the lock to close this race.
+ */
spin_lock_irq(&task->sighand->siglock);
- if (__fatal_signal_pending(task))
- wake_up_state(task, __TASK_TRACED);
- else
- task->state = TASK_TRACED;
+ if (task->state == __TASK_TRACED) {
+ if (__fatal_signal_pending(task))
+ wake_up_state(task, __TASK_TRACED);
+ else
+ task->state = TASK_TRACED;
+ }
spin_unlock_irq(&task->sighand->siglock);
}
--
2.12.2.715.g7642488e1d-goog
next prev parent reply index
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-21 18:47 [PATCH] " bsegall
2017-02-22 16:55 ` Oleg Nesterov
2017-02-22 17:03 ` Oleg Nesterov
2017-02-22 17:56 ` bsegall
2017-02-24 16:36 ` Oleg Nesterov
2017-02-27 18:08 ` bsegall
2017-04-04 21:47 ` bsegall [this message]
2017-04-04 21:53 ` [PATCHv2] " Andrew Morton
2017-04-05 12:36 ` Oleg Nesterov
2017-04-05 12:30 ` Oleg Nesterov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xm26y3vfhmkp.fsf_-_@bsegall-linux.mtv.corp.google.com \
--to=bsegall@google.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=roland@hack.frob.com \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
LKML Archive on lore.kernel.org
Archives are clonable:
git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
# If you have public-inbox 1.1+ installed, you may
# initialize and index your mirror using the following commands:
public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
linux-kernel@vger.kernel.org
public-inbox-index lkml
Example config snippet for mirrors
Newsgroup available over NNTP:
nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel
AGPL code for this site: git clone https://public-inbox.org/public-inbox.git