[PATCH 1/7] Revert "proc/wchan: use printk format instead of lookup_symbol_name()"

Peter Zijlstra
2021-10-08T11:19:28Z

From: Kees Cook <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>
Reported-by: Vito Caputo <vcaputo@pengaru.com>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
---
fs/proc/base.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)

--- 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_fil
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 (wchan)
- seq_printf(m, "%ps", (void *) wchan);
- else
- seq_putc(m, '0');
+ if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+ goto print0;

+ 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 */