[PATCH 4.4 078/162] fs/proc: Stop reporting eip and esp in /proc/PID/stat

From: Greg Kroah-Hartman
Date: Thu Dec 19 2019 - 14:10:20 EST


From: Andy Lutomirski <luto@xxxxxxxxxx>

commit 0a1eb2d474edfe75466be6b4677ad84e5e8ca3f5 upstream.

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
CONFIG_THREAD_INFO_IN_TASK=y, it can OOPS, too.

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

Reported-by: Jann Horn <jann@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Linux API <linux-api@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/a5fed4c3f4e33ed25d4bb03567e329bc5a712bcc.1475257877.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: zhangyi (F) <yi.zhang@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/proc/array.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -425,10 +425,11 @@ static int do_task_stat(struct seq_file
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);