From: Kees Cook <keescook@chromium.org>
To: Len Baker <len.baker@gmx.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
Hans de Goede <hdegoede@redhat.com>,
Mark Gross <mgross@linux.intel.com>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
ibm-acpi-devel@lists.sourceforge.net,
platform-driver-x86@vger.kernel.org,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] platform/x86: thinkpad_acpi: Prefer struct_size over open coded arithmetic
Date: Sun, 19 Sep 2021 22:58:07 -0700 [thread overview]
Message-ID: <202109192246.B438B42EF@keescook> (raw)
In-Reply-To: <20210918150500.21530-1-len.baker@gmx.com>
On Sat, Sep 18, 2021 at 05:05:00PM +0200, Len Baker wrote:
> 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@gmx.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));
Whoa. I have so many questions... :)
>
> 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);
Whoa, this needs a lot more detail in the changelog if this is actually
correct. The original code doesn't seem to match the comment? (Where is
the +1?) So is this also a bug-fix?
(I see the caller uses +2? Why? It seems to be using each of hotkey_attributes,
plus 1 more attr, plus a final NULL?)
> 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;
The caller also never sets a name?
Why is struct attribute_set_obj marked as __packed?
>
> return &sobj->s;
> --
> 2.25.1
>
--
Kees Cook
next prev parent reply other threads:[~2021-09-20 5:58 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-18 15:05 [PATCH] platform/x86: thinkpad_acpi: Prefer struct_size over open coded arithmetic Len Baker
2021-09-20 5:58 ` Kees Cook [this message]
2021-09-21 13:46 ` Hans de Goede
2021-09-21 15:15 ` Greg KH
2021-09-21 15:38 ` Hans de Goede
2021-09-21 15:45 ` Greg KH
2021-09-25 10:40 ` Len Baker
2021-09-25 11:07 ` Greg KH
2021-09-25 13:33 ` Len Baker
2021-09-25 10:37 ` Len Baker
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