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

[Kees Cook <keescook@chromium.org>]

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@linux-foundation.org>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.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