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

From: Andy Lutomirski <luto@kernel.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 <redacted>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Thomas Gleixner <redacted>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <redacted>
Cc: Kees Cook <redacted>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux API <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Tycho Andersen <redacted>
Link: http://lkml.kernel.org/r/a5fed4c3f4e33ed25d4bb03567e329bc5a712bcc.1475257877.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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);