linux-kernel - [PATCH] vme: Fix integer overflow checking in vme_check

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Message-ID: <20170930112741.6wmswvk25j7o44ui@mwanda>
Date:   Sat, 30 Sep 2017 14:27:41 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Martyn Welch <martyn@...chs.me.uk>,
        Dmitry Kalinkin <dmitry.kalinkin@...il.com>
Cc:     Manohar Vanga <manohar.vanga@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: [PATCH] vme: Fix integer overflow checking in vme_check_window()

The controversial part of this patch is that I've changed it so we now
prevent integer overflows for VME_USER types and before we didn't.  I
view it as kernel-hardening.  I looked at a couple places that used
VME_USER types and they seemed pretty suspicious so I'm pretty sure
preventing overflows here is a good idea.

The most common problem which this function is for cases like VME_A16
where we don't put an upper bound on "size" so you could have "size" set
to U64_MAX and a valid vme_base would overflow the "vme_base + size"
into the valid range as well.

In the VME_A64 case, the integer overflow checking doesn't work because
"U64_MAX + 1" has an integer overflow and it's just a complicated way of
saying zero.  That VME_A64 case is sort of interesting as well because
there is a VME_A64_MAX define which is set to "U64_MAX + 1".  The
compiler will never let anyone use it since it can't be stored in a u64
variable...  With my patch it's now limited to just U64_MAX.

Anyway, I put one integer overflow check at the start of the function
and deleted all existing checks.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/drivers/vme/vme.c b/drivers/vme/vme.c
index 6a3ead42aba8..5b4c898d7509 100644
--- a/drivers/vme/vme.c
+++ b/drivers/vme/vme.c
@@ -208,29 +208,27 @@ int vme_check_window(u32 aspace, unsigned long long vme_base,
 {
 	int retval = 0;

+	if (vme_base + size < size)
+		return -EINVAL;
+
 	switch (aspace) {
 	case VME_A16:
-		if (((vme_base + size) > VME_A16_MAX) ||
-				(vme_base > VME_A16_MAX))
+		if (vme_base + size > VME_A16_MAX)
 			retval = -EFAULT;
 		break;
 	case VME_A24:
-		if (((vme_base + size) > VME_A24_MAX) ||
-				(vme_base > VME_A24_MAX))
+		if (vme_base + size > VME_A24_MAX)
 			retval = -EFAULT;
 		break;
 	case VME_A32:
-		if (((vme_base + size) > VME_A32_MAX) ||
-				(vme_base > VME_A32_MAX))
+		if (vme_base + size > VME_A32_MAX)
 			retval = -EFAULT;
 		break;
 	case VME_A64:
-		if ((size != 0) && (vme_base > U64_MAX + 1 - size))
-			retval = -EFAULT;
+		/* The VME_A64_MAX limit is actually U64_MAX + 1 */
 		break;
 	case VME_CRCSR:
-		if (((vme_base + size) > VME_CRCSR_MAX) ||
-				(vme_base > VME_CRCSR_MAX))
+		if (vme_base + size > VME_CRCSR_MAX)
 			retval = -EFAULT;
 		break;
 	case VME_USER1: