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Subject[tip:mm/urgent] fs/proc: Stop reporting eip and esp in /proc/PID/stat
Commit-ID:  0a1eb2d474edfe75466be6b4677ad84e5e8ca3f5
Gitweb: http://git.kernel.org/tip/0a1eb2d474edfe75466be6b4677ad84e5e8ca3f5
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Fri, 30 Sep 2016 10:58:56 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 20 Oct 2016 09:21:41 +0200

fs/proc: Stop reporting eip and esp in /proc/PID/stat

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@thejh.net>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux API <linux-api@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Tycho Andersen <tycho.andersen@canonical.com>
Link: http://lkml.kernel.org/r/a5fed4c3f4e33ed25d4bb03567e329bc5a712bcc.1475257877.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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 89600fd..81818ad 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -412,10 +412,11 @@ 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);
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