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Mon, 06 Jul 2026 08:59:00 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 06 Jul 2026 11:58:59 -0400 Message-Id: Subject: Re: [PATCH] HID: bpf: Fix signedness bug in hid_bpf_hw_request From: "Emil Tsalapatis" To: "Guangshuo Li" , "Jiri Kosina" , "Benjamin Tissoires" , "Kees Cook" , "Puranjay Mohan" , "Johan Hovold" , , , X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260704160703.156298-1-lgs201920130244@gmail.com> In-Reply-To: <20260704160703.156298-1-lgs201920130244@gmail.com> On Sat Jul 4, 2026 at 12:07 PM EDT, Guangshuo Li wrote: > hid_bpf_hw_request() clamps the return value of hid_hw_raw_request() to > the size of the caller supplied buffer before copying data back to the > BPF buffer. > > However, ret is signed while size is unsigned. If hid_hw_raw_request() > returns a negative error code, the comparison promotes ret to size_t. > This makes the negative value look like a very large positive value, so > the error is clamped to size. The following memcpy() then treats the > failed request as a successful transfer and copies stale data back to > the caller. > > Only clamp positive return values. This preserves negative error codes > while still preventing oversized successful returns from overflowing the > caller supplied buffer. > > Fixes: 2b658c1c442e ("HID: bpf: prevent buffer overflow in hid_hw_request= ") > Signed-off-by: Guangshuo Li > --- > drivers/hid/bpf/hid_bpf_dispatch.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf= _dispatch.c > index d0130658091b..b13f911e5944 100644 > --- a/drivers/hid/bpf/hid_bpf_dispatch.c > +++ b/drivers/hid/bpf/hid_bpf_dispatch.c > @@ -446,7 +446,7 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf= , size_t buf__sz, > (u64)(long)ctx, > true); /* prevent infinite recursions */ > =20 > - if (ret > size) > + if (ret > 0 && ret > size) > ret =3D size; I think this is making the code more difficult to write. Why not add a label right before the cleanup at the end of the function, then jump to it on error like so: if (ret < 0) goto done; if (ret > size) ret =3D size; if (ret > 0) memcpy(...); done: kfree(dma_data); return ret; > if (ret > 0) > memcpy(buf, dma_data, ret);