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Subject[PATCH v4 7/9] vsprintf: Factor out %pO handler as kobject_string()
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 <>
Cc: Linus Torvalds <>
Cc: Tobin Harding <>
Cc: Kees Cook <>
lib/vsprintf.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index f20eaa3f0092..3551b7957d9e 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1772,6 +1772,19 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,

static noinline_for_stack
+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);
+ }
+ WARN_ONCE(1, "Unsupported pointer format specifier: %%pO%c\n", fmt[1]);
+ return buf;
+static noinline_for_stack
char *pointer_string(char *buf, char *end, const void *ptr,
struct printf_spec spec)
@@ -1982,10 +1995,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
case 'G':
return flags_string(buf, end, ptr, 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);
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