linux-kernel - [PATCH 4.4 4/7] fs/proc: Stop reporting eip and esp in /proc/PID/stat

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Date:   Mon, 2 Dec 2019 16:35:16 +0800
From:   "zhangyi (F)" <yi.zhang@...wei.com>
To:     <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <luto@...nel.org>, <adobriyan@...il.com>,
        <akpm@...ux-foundation.org>, <vbabka@...e.cz>,
        <peterz@...radead.org>, <bigeasy@...utronix.de>, <mhocko@...e.com>,
        <john.ogness@...utronix.de>, <yi.zhang@...wei.com>,
        <nixiaoming@...wei.com>
Subject: [PATCH 4.4 4/7] fs/proc: Stop reporting eip and esp in /proc/PID/stat

From: Andy Lutomirski <luto@...nel.org>

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@...jh.net>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Linux API <linux-api@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Tycho Andersen <tycho.andersen@...onical.com>
Link: http://lkml.kernel.org/r/a5fed4c3f4e33ed25d4bb03567e329bc5a712bcc.1475257877.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
---
 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 60cbaa821164..618c83f1866d 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -425,10 +425,11 @@ 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);
-- 
2.17.2