[PATCH 1/3] Revert "proc/wchan: use printk format instead of lookup_symbol_name()"

From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>,
	kernel test robot <oliver.sang@intel.com>,
	Vito Caputo <vcaputo@pengaru.com>, Jann Horn <jannh@google.com>,
	stable@vger.kernel.org, Helge Deller <deller@gmx.de>,
	Qi Zheng <zhengqi.arch@bytedance.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	"Tobin C. Harding" <me@tobin.cc>,
	Tycho Andersen <tycho@tycho.pizza>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Mark Rutland <mark.rutland@arm.com>, Jens Axboe <axboe@kernel.dk>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	Stefan Metzmacher <metze@samba.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Michal Hocko <mhocko@suse.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Ohhoon Kwon <ohoono.kwon@samsung.com>,
	YiFei Zhu <yifeifz2@illinois.edu>,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
	x86@kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 1/3] Revert "proc/wchan: use printk format instead of lookup_symbol_name()"
Date: Thu, 23 Sep 2021 23:20:04 -0700	[thread overview]
Message-ID: <20210924062006.231699-2-keescook@chromium.org> (raw)
In-Reply-To: <20210924062006.231699-1-keescook@chromium.org>

This reverts commit 152c432b128cb043fc107e8f211195fe94b2159c.

When a kernel address couldn't be symbolized for /proc/$pid/wchan, it
would leak the raw value, a potential information exposure. This is a
regression compared to the safer pre-v5.12 behavior.

Reported-by: kernel test robot <oliver.sang@intel.com>
Link: https://lore.kernel.org/all/20210103142726.GC30643@xsang-OptiPlex-9020/
Reported-by: Vito Caputo <vcaputo@pengaru.com>
Link: https://lore.kernel.org/lkml/20210921193249.el476vlhg5k6lfcq@shells.gnugeneration.com/
Reported-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/lkml/CAG48ez2zC=+PuNgezH53HBPZ8CXU5H=vkWx7nJs60G8RXt3w0Q@mail.gmail.com/
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/proc/base.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 533d5836eb9a..1f394095eb88 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -67,6 +67,7 @@
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/rcupdate.h>
+#include <linux/kallsyms.h>
 #include <linux/stacktrace.h>
 #include <linux/resource.h>
 #include <linux/module.h>
@@ -386,17 +387,19 @@ 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];
 
-	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
-		wchan = get_wchan(task);
-	else
-		wchan = 0;
+	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+		goto print0;
 
-	if (wchan)
-		seq_printf(m, "%ps", (void *) wchan);
-	else
-		seq_putc(m, '0');
+	wchan = get_wchan(task);
+	if (wchan && !lookup_symbol_name(wchan, symname)) {
+		seq_puts(m, symname);
+		return 0;
+	}
 
+print0:
+	seq_putc(m, '0');
 	return 0;
 }
 #endif /* CONFIG_KALLSYMS */
-- 
2.30.2

