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vsprintf: Consistent %pK handling for kptr_restrict == 0

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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: ef0010a309 ("vsprintf: don't use 'restricted_pointer()' when not restricting")
Link: http://lkml.kernel.org/r/20190417115350.20479-3-pmladek@suse.com
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Tobin C . Harding" <me@tobin.cc>
Cc: Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Petr Mladek 2019-04-17 13:53:42 +02:00
parent 6eea242f9b
commit 1ac2f9789c
1 changed files with 2 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
lib/vsprintf.c
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@ -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);