[PATCH v5 08/11] vsprintf: Factor out %pO handler as kobject_string()

From: Petr Mladek
Date: Wed Apr 25 2018 - 07:15:08 EST

Move code from the long pointer() function. We are going to add a check for
the access to the address that will make it even more complicated.

Also it is better to warn about unknown specifier instead of falling
back to the %p behavior. It will help people to understand what is
going wrong. They expect some device node names and not a pointer
in this situation.

In fact, this avoids leaking the address when invalid %pO format
specifier is used. The old code fallen back to printing the
non-hashed value.

Fixes: commit 7b1924a1d930eb27f ("vsprintf: add printk specifier %px")
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Tobin Harding <me@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
lib/vsprintf.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e58436ef9f7f..3536796c483c 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1769,6 +1769,17 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
return widen_string(buf, buf - buf_start, end, spec);

+static char *kobject_string(char *buf, char *end, void *ptr,
+ struct printf_spec spec, const char *fmt)
+ switch (fmt[1]) {
+ case 'F':
+ return device_node_string(buf, end, ptr, spec, fmt + 1);
+ }
+ return valid_string(buf, end, "(%pO?)", spec);
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
@@ -1962,10 +1973,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
case 'G':
return flags_string(buf, end, ptr, spec, fmt);
case 'O':
- switch (fmt[1]) {
- case 'F':
- return device_node_string(buf, end, ptr, spec, fmt + 1);
- }
+ return kobject_string(buf, end, ptr, spec, fmt);
case 'x':
return pointer_string(buf, end, ptr, spec);