linux-kernel - [kernel-hardening] [RFC V2 4/6] lib: vsprintf: default kptr

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Message-Id: <1506816410-10230-5-git-send-email-me@tobin.cc>
Date:   Sun,  1 Oct 2017 11:06:48 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     "Tobin C. Harding" <me@...in.cc>,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        William Roberts <william.c.roberts@...el.com>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>
Subject: [kernel-hardening] [RFC V2 4/6] lib: vsprintf: default kptr_restrict to the maximum value

Set the initial value of kptr_restrict to the maximum
setting rather than the minimum setting, to ensure that
early boot logging is not leaking information.

Signed-off-by: Tobin C. Harding <me@...in.cc>
---
 lib/vsprintf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 0271223..e009325 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -396,7 +396,7 @@ struct printf_spec {
 #define FIELD_WIDTH_MAX ((1 << 23) - 1)
 #define PRECISION_MAX ((1 << 15) - 1)
 
-int kptr_restrict __read_mostly;
+int kptr_restrict __read_mostly = 4; /* maximum setting */
 
 /*
  * return non-zero if we should cleanse pointers for %p and %pK specifiers.
-- 
2.7.4