From: Alan Stern <stern@rowland.harvard.edu>
To: Andrej Shadura <andrew.shadura@collabora.co.uk>
Cc: "Jiří Kosina" <jikos@kernel.org>,
linux-input@vger.kernel.org, linux-usb@vger.kernel.org,
stable@vger.kernel.org, kernel@collabora.com
Subject: Re: [PATCH v2 1/2] HID: u2fzero: explicitly check for errors
Date: Mon, 18 Oct 2021 10:15:27 -0400 [thread overview]
Message-ID: <20211018141527.GA1048431@rowland.harvard.edu> (raw)
In-Reply-To: <20211018122144.25131-1-andrew.shadura@collabora.co.uk>
On Mon, Oct 18, 2021 at 02:21:43PM +0200, Andrej Shadura wrote:
> The previous commit fixed handling of incomplete packets but broke error
> handling: offsetof returns an unsigned value (size_t), but when compared
> against the signed return value, the return value is interpreted as if
> it were unsigned, so negative return values are never less than the
> offset.
>
> Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
> Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
> Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
> ---
> drivers/hid/hid-u2fzero.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
> index d70cd3d7f583..5145d758bea0 100644
> --- a/drivers/hid/hid-u2fzero.c
> +++ b/drivers/hid/hid-u2fzero.c
> @@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
> ret = u2fzero_recv(dev, &req, &resp);
>
> /* ignore errors or packets without data */
> - if (ret < offsetof(struct u2f_hid_msg, init.data))
> + if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
Although the patch description does a good job of explaining what's
happening, someone merely reading the code will most likely not
understand.
One alternative is to add a comment. Another is simply to force a
signed integer comparison:
if (ret < (ssize_t) offsetof(...
Alan Stern
next prev parent reply other threads:[~2021-10-18 14:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-18 12:21 [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Andrej Shadura
2021-10-18 12:21 ` [PATCH v2 2/2] HID: u2fzero: properly handle timeouts in usb_submit_urb Andrej Shadura
2021-10-18 14:15 ` Alan Stern [this message]
2021-10-18 14:17 ` [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Andrej Shadura
2021-10-18 14:38 ` Alan Stern
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