vsprintf: Consistent %pK handling for kptr_restrict == 0

restricted_pointer() pretends that it prints the address when kptr_restrict
is set to zero. But it is never called in this situation. Instead,
pointer() falls back to ptr_to_id() and hashes the pointer.

This patch removes the potential confusion. klp_restrict is checked only
in restricted_pointer().

It actually fixes a small race when the address might get printed unhashed:

CPU0                            CPU1

pointer()
  if (!kptr_restrict)
     /* for example set to 2 */
  restricted_pointer()
				/* echo 0 >/proc/sys/kernel/kptr_restrict */
				proc_dointvec_minmax_sysadmin()
				  klpr_restrict = 0;
    switch(kptr_restrict)
      case 0:
	break:

    number()

Fixes: ef0010a30935de4e0211 ("vsprintf: don't use 'restricted_pointer()' when not restricting")
Link: http://lkml.kernel.org/r/[email protected]
To: Andy Shevchenko <[email protected]>
To: Rasmus Villemoes <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: "Tobin C . Harding" <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: [email protected]
Cc: Kees Cook <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>

1 files changed, 2 insertions, 4 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index eb7b4a06e1f0..2af48948a973 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -725,8 +725,8 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
 {
 	switch (kptr_restrict) {
 	case 0:
-		/* Always print %pK values */
-		break;
+		/* Handle as %p, hash and do _not_ leak addresses. */
+		return ptr_to_id(buf, end, ptr, spec);
 	case 1: {
 		const struct cred *cred;
 
@@ -2041,8 +2041,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return buf;
 		}
 	case 'K':
-		if (!kptr_restrict)
-			break;
 		return restricted_pointer(buf, end, ptr, spec);
 	case 'N':
 		return netdev_bits(buf, end, ptr, spec, fmt);