linux-hardening - [PATCH] platform/x86: thinkpad_acpi: Prefer struct

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Date:   Sat, 18 Sep 2021 17:05:00 +0200
From:   Len Baker <len.baker@....com>
To:     Henrique de Moraes Holschuh <hmh@....eng.br>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>
Cc:     Len Baker <len.baker@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        ibm-acpi-devel@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] platform/x86: thinkpad_acpi: Prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, switch to flexible array member in the struct attribute_set_obj and
refactor the code accordingly to use the struct_size() helper instead of
the argument "size + count * size" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@....com>
---
 drivers/platform/x86/thinkpad_acpi.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 50ff04c84650..ed0b01ead796 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -1008,7 +1008,7 @@ struct attribute_set {

 struct attribute_set_obj {
 	struct attribute_set s;
-	struct attribute *a;
+	struct attribute *a[];
 } __attribute__((packed));

 static struct attribute_set *create_attr_set(unsigned int max_members,
@@ -1020,13 +1020,11 @@ static struct attribute_set *create_attr_set(unsigned int max_members,
 		return NULL;

 	/* Allocates space for implicit NULL at the end too */
-	sobj = kzalloc(sizeof(struct attribute_set_obj) +
-		    max_members * sizeof(struct attribute *),
-		    GFP_KERNEL);
+	sobj = kzalloc(struct_size(sobj, a, max_members + 1), GFP_KERNEL);
 	if (!sobj)
 		return NULL;
 	sobj->s.max_members = max_members;
-	sobj->s.group.attrs = &sobj->a;
+	sobj->s.group.attrs = sobj->a;
 	sobj->s.group.name = name;

 	return &sobj->s;
--
2.25.1