[PATCH] HID: u2fzero: ignore incomplete packets without data

[PATCH] HID: u2fzero: ignore incomplete packets without data

[Andrej Shadura]

Since the actual_length calculation is performed unsigned, packets
shorter than 7 bytes (e.g. packets without data or otherwise truncated)
or non-received packets ("zero" bytes) can cause buffer overflow.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=214437
Fixes: 42337b9d4d958("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 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
index 95e0807878c7..d70cd3d7f583 100644
--- a/drivers/hid/hid-u2fzero.c
+++ b/drivers/hid/hid-u2fzero.c
@@ -198,7 +198,9 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
 	}
 
 	ret = u2fzero_recv(dev, &req, &resp);
-	if (ret < 0)
+
+	/* ignore errors or packets without data */
+	if (ret < offsetof(struct u2f_hid_msg, init.data))
 		return 0;
 
 	/* only take the minimum amount of data it is safe to take */
-- 
2.31.1

Re: [PATCH] HID: u2fzero: ignore incomplete packets without data

[Andrej Shadura]

Hi again,

On 16/09/2021 17:33, Andrej Shadura wrote:
> Since the actual_length calculation is performed unsigned, packets
> shorter than 7 bytes (e.g. packets without data or otherwise truncated)
> or non-received packets ("zero" bytes) can cause buffer overflow.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=214437
> Fixes: 42337b9d4d958("HID: add driver for U2F Zero built-in LED and RNG")
> Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>

Having sent the email I realised I forgot to describe the actual
situation when I ran into this bug. It happened after I inserted and
removed the device multiple times very quickly. I know it’s not
extremely reliable way to reproduce it, and it rarely happened to me
before for some reason, but on the current kernel (5.11.0) I was able to
cause the crash every time I tried.

-- 
Cheers,
  Andrej

Re: [PATCH] HID: u2fzero: ignore incomplete packets without data

[Jiri Kosina]

On Thu, 16 Sep 2021, Andrej Shadura wrote:

> Since the actual_length calculation is performed unsigned, packets
> shorter than 7 bytes (e.g. packets without data or otherwise truncated)
> or non-received packets ("zero" bytes) can cause buffer overflow.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=214437
> Fixes: 42337b9d4d958("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 | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
> index 95e0807878c7..d70cd3d7f583 100644
> --- a/drivers/hid/hid-u2fzero.c
> +++ b/drivers/hid/hid-u2fzero.c
> @@ -198,7 +198,9 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
>  	}
>  
>  	ret = u2fzero_recv(dev, &req, &resp);
> -	if (ret < 0)
> +
> +	/* ignore errors or packets without data */
> +	if (ret < offsetof(struct u2f_hid_msg, init.data))
>  		return 0;
>  

Applied, thanks.

-- 
Jiri Kosina
SUSE Labs