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Subject[PATCH v4 2/9] vsprintf: Consistent %pK handling for kptr_restrict == 0
Date
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 should actually fix 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: commit ef0010a30935de4e0211 ("vsprintf: don't use 'restricted_pointer()' when not restricting")
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tobin Harding <me@tobin.cc>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
lib/vsprintf.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index c0c677c6a833..9ade2c4f21ba 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -637,7 +637,8 @@ static int __init initialize_ptr_random(void)
early_initcall(initialize_ptr_random);

/* Maps a pointer to a 32 bit unique identifier. */
-static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
+static char *ptr_to_id(char *buf, char *end,
+ const void *ptr, struct printf_spec spec)
{
unsigned long hashval;
const int default_width = 2 * sizeof(ptr);
@@ -1426,8 +1427,8 @@ 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;

@@ -1931,8 +1932,6 @@ 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, fmt);
--
2.13.6
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