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Date: Wed, 30 Sep 2015 15:59:17 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...capital.net>,
Kees Cook <keescook@...omium.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Borislav Petkov <bp@...en8.de>,
Denys Vlasenko <dvlasenk@...hat.com>,
"x86@...nel.org" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Andrey Konovalov <andreyknvl@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Andi Kleen <ak@...ux.intel.com>,
kasan-dev <kasan-dev@...glegroups.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH v2] fs/proc: Don't expose absolute kernel addresses via wchan
* Thomas Gleixner <tglx@...utronix.de> wrote:
> On Wed, 30 Sep 2015, Ingo Molnar wrote:
> > diff --git a/fs/proc/array.c b/fs/proc/array.c
> > index f60f0121e331..99082730b2ac 100644
> > --- a/fs/proc/array.c
> > +++ b/fs/proc/array.c
> > @@ -507,7 +507,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
> > seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL);
> > seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL);
> > seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL);
> > - seq_put_decimal_ull(m, ' ', wchan);
> > + seq_puts(m, " 0"); /* Used to be numeric wchan - replaced by /proc/PID/wchan */
>
> That should get rid of all wchan usage in do_task_stat()
Indeed - updated patch attached.
Thanks,
Ingo
================================>
>From 985037cd05b379240dd381b29c2525758c665bb0 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...nel.org>
Date: Wed, 30 Sep 2015 09:15:37 +0200
Subject: [PATCH] fs/proc: Don't expose absolute kernel addresses via wchan
So wchan leaks absolute kernel addresses to unprivileged
user-space, of kernel functions that sleep:
static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
unsigned long wchan;
char symname[KSYM_NAME_LEN];
wchan = get_wchan(task);
if (lookup_symbol_name(wchan, symname) < 0) {
if (!ptrace_may_access(task, PTRACE_MODE_READ))
return 0;
seq_printf(m, "%lu", wchan);
} else {
seq_printf(m, "%s", symname);
}
return 0;
}
So for example it trivially leaks the KASLR offset to any local
attacker:
fomalhaut:~> printf "%016lx\n" $(cat /proc/$$/stat | cut -d' ' -f35)
ffffffff8123b380
Most real-life uses of wchan are symbolic:
ps -eo pid:10,tid:10,wchan:30,comm
and procps uses /proc/PID/wchan, not the absolute address in
/proc/PID/stat:
triton:~/tip> strace -f ps -eo pid:10,tid:10,wchan:30,comm 2>&1 | grep wchan | tail -1
open("/proc/30833/wchan", O_RDONLY) = 6
These days there's very little legitimate reason user-space
would be interested in the absolute address. The absolute
address is mostly historic: from the days when we didn't have
kallsyms and user-space procps had to do the decoding itself via
the System.map.
So this patch sets all numeric output to 0 and keeps the
symbolic output in /proc/PID/wchan.
( The absolute sleep address can generally still be profiled via
perf, by tasks with sufficient privileges. )
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Kostya Serebryany <kcc@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kasan-dev <kasan-dev@...glegroups.com>
Cc: linux-kernel@...r.kernel.org
Link: http://lkml.kernel.org/r/20150930071537.GA19048@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
fs/proc/array.c | 6 ++----
fs/proc/base.c | 7 +------
2 files changed, 3 insertions(+), 10 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index f60f0121e331..ad5ad1e376ad 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -375,7 +375,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task, int whole)
{
- unsigned long vsize, eip, esp, wchan = ~0UL;
+ unsigned long vsize, eip, esp;
int priority, nice;
int tty_pgrp = -1, tty_nr = 0;
sigset_t sigign, sigcatch;
@@ -454,8 +454,6 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
unlock_task_sighand(task, &flags);
}
- if (permitted && (!whole || num_threads < 2))
- wchan = get_wchan(task);
if (!whole) {
min_flt = task->min_flt;
maj_flt = task->maj_flt;
@@ -507,7 +505,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL);
seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL);
seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL);
- seq_put_decimal_ull(m, ' ', wchan);
+ seq_puts(m, " 0"); /* Used to be numeric wchan - replaced by /proc/PID/wchan */
seq_put_decimal_ull(m, ' ', 0);
seq_put_decimal_ull(m, ' ', 0);
seq_put_decimal_ll(m, ' ', task->exit_signal);
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b25eee4cead5..2fdbf303e3eb 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -430,13 +430,8 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
wchan = get_wchan(task);
- if (lookup_symbol_name(wchan, symname) < 0) {
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return 0;
- seq_printf(m, "%lu", wchan);
- } else {
+ if (!lookup_symbol_name(wchan, symname))
seq_printf(m, "%s", symname);
- }
return 0;
}
--
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