From: Kees Cook <keescook@chromium.org>
To: David Herrmann <dh.herrmann@gmail.com>
Cc: Laura Abbott <labbott@redhat.com>,
linux-input <linux-input@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Jiri Kosina <jikos@kernel.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Xiongfeng Wang <xiongfeng.wang@linaro.org>
Subject: Re: [PATCH] Revert "HID: uhid: use strlcpy() instead of strncpy()"
Date: Wed, 14 Nov 2018 17:09:42 -0600 [thread overview]
Message-ID: <CAGXu5jJJGg5_crJ3v+AG5JZWVGLpDvZGr0UVyurzFxcv9Fwa5A@mail.gmail.com> (raw)
In-Reply-To: <ea944fb3-0cd9-e6e6-5449-faab7c9603c1@redhat.com>
On Wed, Nov 14, 2018 at 9:40 AM, Laura Abbott <labbott@redhat.com> wrote:
> On 11/14/18 5:16 AM, David Herrmann wrote:
>>
>> This reverts commit 336fd4f5f25157e9e8bd50e898a1bbcd99eaea46.
>>
>> Please note that `strlcpy()` does *NOT* do what you think it does.
>> strlcpy() *ALWAYS* reads the full input string, regardless of the
>> 'length' parameter. That is, if the input is not zero-terminated,
>> strlcpy() will *READ* beyond input boundaries. It does this, because it
>> always returns the size it *would* copy if the target was big enough,
>> not the truncated size it actually copied.
>>
>> The original code was perfectly fine. The hid device is
>> zero-initialized and the strncpy() functions copied up to n-1
>> characters. The result is always zero-terminated this way.
>>
>> This is the third time someone tried to replace strncpy with strlcpy in
>> this function, and gets it wrong. I now added a comment that should at
>> least make people reconsider.
>>
>
> Can we switch to strscpy instead? This will quiet gcc and avoid the
> issues with strlcpy.
Yes please: it looks like these strings are expected to be NUL
terminated, so strscpy() without the "- 1" and min() logic would be
the correct solution here. If @hid is already zero, then this would
just be:
strscpy(hid->name, ev->u.create2.name, sizeof(hid->name));
strscpy(hid->phys, ev->u.create2.phys, sizeof(hid->phys));
strscpy(hid->uniq, ev->u.create2.uniq, sizeof(hid->uniq));
If they are NOT NUL terminated, then keep using strncpy() but mark the
fields in the struct with the __nonstring attribute.
-Kees
>
>
>> Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
>> ---
>> drivers/hid/uhid.c | 13 +++++++------
>> 1 file changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
>> index fefedc0b4dc6..0dfdd0ac7120 100644
>> --- a/drivers/hid/uhid.c
>> +++ b/drivers/hid/uhid.c
>> @@ -496,12 +496,13 @@ static int uhid_dev_create2(struct uhid_device
>> *uhid,
>> goto err_free;
>> }
>> - len = min(sizeof(hid->name), sizeof(ev->u.create2.name));
>> - strlcpy(hid->name, ev->u.create2.name, len);
>> - len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys));
>> - strlcpy(hid->phys, ev->u.create2.phys, len);
>> - len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq));
>> - strlcpy(hid->uniq, ev->u.create2.uniq, len);
>> + /* @hid is zero-initialized, strncpy() is correct, strlcpy() not
>> */
>> + len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1;
>> + strncpy(hid->name, ev->u.create2.name, len);
>> + len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1;
>> + strncpy(hid->phys, ev->u.create2.phys, len);
>> + len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1;
>> + strncpy(hid->uniq, ev->u.create2.uniq, len);
>> hid->ll_driver = &uhid_hid_driver;
>> hid->bus = ev->u.create2.bus;
>>
>
--
Kees Cook
next prev parent reply other threads:[~2018-11-14 23:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 13:16 [PATCH] Revert "HID: uhid: use strlcpy() instead of strncpy()" David Herrmann
2018-11-14 15:40 ` Laura Abbott
2018-11-14 23:09 ` Kees Cook [this message]
2018-11-15 11:55 ` David Herrmann
2018-11-16 1:10 ` Kees Cook
2018-11-19 13:33 ` Jiri Kosina
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