linux-kernel - [PATCH 4/4] perf: Use new infrastructure to fix deadlocks in execve

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Date:   Tue, 10 Mar 2020 18:45:56 +0100
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Yuyang Du <duyuyang@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian Kellner <christian@...lner.me>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: [PATCH 4/4] perf: Use new infrastructure to fix deadlocks in execve

This changes perf_event_set_clock to use the new exec_update_mutex
instead of cred_guard_mutex.

This should be safe, as the credentials are only used for reading.

Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
---
 kernel/events/core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2173c23..c37f6eb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1248,7 +1248,7 @@ static void put_ctx(struct perf_event_context *ctx)
  * function.
  *
  * Lock order:
- *    cred_guard_mutex
+ *    exec_update_mutex
  *	task_struct::perf_event_mutex
  *	  perf_event_context::mutex
  *	    perf_event::child_mutex;
@@ -11254,14 +11254,14 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
 	}
 
 	if (task) {
-		err = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
+		err = mutex_lock_interruptible(&task->signal->exec_update_mutex);
 		if (err)
 			goto err_task;
 
 		/*
 		 * Reuse ptrace permission checks for now.
 		 *
-		 * We must hold cred_guard_mutex across this and any potential
+		 * We must hold exec_update_mutex across this and any potential
 		 * perf_install_in_context() call for this new event to
 		 * serialize against exec() altering our credentials (and the
 		 * perf_event_exit_task() that could imply).
@@ -11550,7 +11550,7 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
 	mutex_unlock(&ctx->mutex);
 
 	if (task) {
-		mutex_unlock(&task->signal->cred_guard_mutex);
+		mutex_unlock(&task->signal->exec_update_mutex);
 		put_task_struct(task);
 	}
 
@@ -11586,7 +11586,7 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
 		free_event(event);
 err_cred:
 	if (task)
-		mutex_unlock(&task->signal->cred_guard_mutex);
+		mutex_unlock(&task->signal->exec_update_mutex);
 err_task:
 	if (task)
 		put_task_struct(task);
@@ -11891,7 +11891,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
 /*
  * When a child task exits, feed back event values to parent events.
  *
- * Can be called with cred_guard_mutex held when called from
+ * Can be called with exec_update_mutex held when called from
  * install_exec_creds().
  */
 void perf_event_exit_task(struct task_struct *child)
-- 
1.9.1