[4.4,4/7] fs/proc: Stop reporting eip and esp in /proc/PID/stat

Commit Message

Zhang Yi Dec. 2, 2019, 8:35 a.m. UTC

From: Andy Lutomirski <[e-mail]>

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 <[e-mail]>
Signed-off-by: Andy Lutomirski <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Linux API <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Tetsuo Handa <[e-mail]>
Cc: Tycho Andersen <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>
Signed-off-by: zhangyi (F) <[e-mail]>
---
 fs/proc/array.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Patch

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);