Merge branch 'core-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull wchan kernel address hiding from Ingo Molnar:
 "This fixes a wchan related information leak in /proc/PID/stat.

  There's a bit of an ABI twist to it: instead of setting the wchan
  field to 0 (which is our usual technique) we set it conditionally to a
  0/1 flag to keep ABI compatibility with older procps versions that
  only fetches /proc/PID/wchan (symbolic names) if the absolute wchan
  address is nonzero"

* 'core-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  fs/proc, core/debug: Don't expose absolute kernel addresses via wchan

2 files changed, 17 insertions, 8 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index f60f0121e331..eed2050db9be 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, wchan = 0;
         int priority, nice;
         int tty_pgrp = -1, tty_nr = 0;
         sigset_t sigign, sigcatch;
@@ -507,7 +507,19 @@ 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);
+
+        /*
+         * We used to output the absolute kernel address, but that's an
+         * information leak - so instead we show a 0/1 flag here, to signal
+         * to user-space whether there's a wchan field in /proc/PID/wchan.
+         *
+         * This works with older implementations of procps as well.
+         */
+        if (wchan)
+                seq_puts(m, " 1");
+        else
+                seq_puts(m, " 0");
+
         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..29595af32866 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -430,13 +430,10 @@ 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 (wchan && ptrace_may_access(task, PTRACE_MODE_READ) && !lookup_symbol_name(wchan, symname))
                 seq_printf(m, "%s", symname);
-        }
+        else
+                seq_putc(m, '0');
 
         return 0;
 }