[PATCH 1/3] proc: Stop reporting eip and esp in /proc/PID/stat

From: Andy Lutomirski
Date: Fri Sep 30 2016 - 13:59:33 EST

Reporting these fields on a non-current task is dangerous. If the
task is in any state other than normal kernel code, they may contain
garbage or even kernel addresses on some architectures. (x86_64
used to do this. I bet lots of architectures still do.) With

As far as I know, there are no use programs that make any material
use of these fields, so just get rid of them.

Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Jann Horn <jann@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
fs/proc/array.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 88c7de12197b..1bb1097e73b7 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -417,10 +417,11 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
mm = get_task_mm(task);
if (mm) {
vsize = task_vsize(mm);
- if (permitted) {
- eip = KSTK_EIP(task);
- esp = KSTK_ESP(task);
- }
+ /*
+ * esp and eip are intentionally zeroed out. There is no
+ * non-racy way to read them without freezing the task.
+ * Programs that need reliable values can use ptrace(2).
+ */

get_task_comm(tcomm, task);