[PATCH] use %pK for /proc/kallsyms and /proc/modules

[Kees Cook <kees.cook@canonical.com>]

Instead of messing with permissions on these files, use %pK for kernel
addresses to reduce potential information leaks that might be used to
help target kernel privilege escalation exploits.

Note that this changes %x to %p, so some legitimately 0 values in
/proc/kallsyms would have changed from 00000000 to "(null)". To avoid
this, "(null)" is not used when using the "K" format. Anything parsing
such addresses should have no problem with this change. (Thanks to Joe
Perches for the suggestion.)

Note that when compiling with -Wformat, these harmless warnings will
be emitted, and can be ignored:
  warning: '0' flag used with ‘%p’ gnu_printf format

Signed-off-by: Kees Cook <kees.cook@canonical.com>
---
 kernel/kallsyms.c |    4 ++--
 kernel/module.c   |    4 ++--
 lib/vsprintf.c    |    2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f6d091..074b762 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -477,11 +477,11 @@ static int s_show(struct seq_file *m, void *p)
 		 */
 		type = iter->exported ? toupper(iter->type) :
 					tolower(iter->type);
-		seq_printf(m, "%0*lx %c %s\t[%s]\n",
+		seq_printf(m, "%0*pK %c %s\t[%s]\n",
 			   (int)(2 * sizeof(void *)),
 			   iter->value, type, iter->name, iter->module_name);
 	} else
-		seq_printf(m, "%0*lx %c %s\n",
+		seq_printf(m, "%0*pK %c %s\n",
 			   (int)(2 * sizeof(void *)),
 			   iter->value, iter->type, iter->name);
 	return 0;
diff --git a/kernel/module.c b/kernel/module.c
index 34e00b7..748465c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1168,7 +1168,7 @@ static ssize_t module_sect_show(struct module_attribute *mattr,
 {
 	struct module_sect_attr *sattr =
 		container_of(mattr, struct module_sect_attr, mattr);
-	return sprintf(buf, "0x%lx\n", sattr->address);
+	return sprintf(buf, "0x%pK\n", sattr->address);
 }
 
 static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
@@ -3224,7 +3224,7 @@ static int m_show(struct seq_file *m, void *p)
 		   mod->state == MODULE_STATE_COMING ? "Loading":
 		   "Live");
 	/* Used by oprofile and other similar tools. */
-	seq_printf(m, " 0x%p", mod->module_core);
+	seq_printf(m, " 0x%pK", mod->module_core);
 
 	/* Taints info */
 	if (mod->taints)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d3023df..288d770 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -991,7 +991,7 @@ static noinline_for_stack
 char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	      struct printf_spec spec)
 {
-	if (!ptr) {
+	if (!ptr && *fmt != 'K') {
 		/*
 		 * Print (null) with the same width as a pointer so it makes
 		 * tabular output look nice.
-- 
1.7.2.3

-- 
Kees Cook
Ubuntu Security Team