Revert "proc/wchan: use printk format instead of lookup_symbol_name()"

This reverts commit 152c432. 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 <[email protected]> Reported-by: Vito Caputo <[email protected]> Reported-by: Jann Horn <[email protected]> Signed-off-by: Kees Cook <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: [email protected] Link: https://lkml.kernel.org/r/[email protected]
amitbern-aws · Oct 15, 2021 · 54354c6 · 54354c6
1 parent 804bccb
commit 54354c6
Showing 1 changed file with 11 additions and 8 deletions.
diff --git 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 */