linux-kernel - [PATCH 4.17 34/70] x86/MCE: Fix stack out-of-bounds write in mce-inject.c: Flags

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Date:   Sun, 24 Jun 2018 23:22:26 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-edac <linux-edac@...r.kernel.org>
Subject: [PATCH 4.17 34/70] x86/MCE: Fix stack out-of-bounds write in mce-inject.c: Flags_read()

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tony Luck <tony.luck@...el.com>

commit 985c78d3ff8e9c74450fa2bb08eb55e680d999ca upstream.

Each of the strings that we want to put into the buf[MAX_FLAG_OPT_SIZE]
in flags_read() is two characters long. But the sprintf() adds
a trailing newline and will add a terminating NUL byte. So
MAX_FLAG_OPT_SIZE needs to be 4.

sprintf() calls vsnprintf() and *that* does return:

" * The return value is the number of characters which would
 * be generated for the given input, excluding the trailing
 * '\0', as per ISO C99."

Note the "excluding".

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Cc: linux-edac <linux-edac@...r.kernel.org>
Link: http://lkml.kernel.org/r/20180427163707.ktaiysvbk3yhk4wm@agluck-desk
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/cpu/mcheck/mce-inject.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/mcheck/mce-inject.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c
@@ -48,7 +48,7 @@ static struct dentry *dfs_inj;
 
 static u8 n_banks;
 
-#define MAX_FLAG_OPT_SIZE	3
+#define MAX_FLAG_OPT_SIZE	4
 #define NBCFG			0x44
 
 enum injection_type {