From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laura Abbott Subject: Re: [PATCH] Revert "HID: uhid: use strlcpy() instead of strncpy()" Date: Wed, 14 Nov 2018 07:40:43 -0800 Message-ID: References: <20181114131642.21425-1-dh.herrmann@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181114131642.21425-1-dh.herrmann@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: David Herrmann , linux-input@vger.kernel.org Cc: linux-kernel@vger.kernel.org, jikos@kernel.org, benjamin.tissoires@redhat.com, Kees Cook List-Id: linux-input@vger.kernel.org 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. > Signed-off-by: David Herrmann > --- > 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; >