linux-hardening - [PATCH v2 4/6] proc: Only report /proc/$pid/wchan when process is blocked

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Date:   Wed, 29 Sep 2021 15:02:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jann Horn <jannh@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Helge Deller <deller@....de>, linux-fsdevel@...r.kernel.org,
        kernel test robot <oliver.sang@...el.com>,
        Vito Caputo <vcaputo@...garu.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Anand K Mistry <amistry@...gle.com>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Alexey Gladkov <legion@...nel.org>,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        "Tobin C. Harding" <me@...in.cc>,
        Tycho Andersen <tycho@...ho.pizza>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mark Rutland <mark.rutland@....com>,
        Jens Axboe <axboe@...nel.dk>,
        Stefan Metzmacher <metze@...ba.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ohhoon Kwon <ohoono.kwon@...sung.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        x86@...nel.org
Subject: [PATCH v2 4/6] proc: Only report /proc/$pid/wchan when process is blocked

The current get_wchan() implementations do their best to avoid problems
when walking a stack given a process in an unknown state, but this is
fragile and unnecessary. It's only useful to report wchan if a process
is actually blocked, so use the new sched_task_get_wchan() instead.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christian Brauner <christian.brauner@...ntu.com>
Cc: Jann Horn <jannh@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Helge Deller <deller@....de>
Cc: linux-fsdevel@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/proc/base.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 1f394095eb88..7853592778b2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -392,7 +392,8 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
 	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
 		goto print0;
 
-	wchan = get_wchan(task);
+	wchan = sched_task_get_wchan(task);
+	/* Must only report symbolized addresses and never raw pointers. */
 	if (wchan && !lookup_symbol_name(wchan, symname)) {
 		seq_puts(m, symname);
 		return 0;
-- 
2.30.2