[PATCH 1/2] HID: bpf: cast size to ssize_t when checking hid_bpf_hw_request

[Benjamin Tissoires <bentiss@kernel.org>]

As reported by Sashiko:
If a transport driver encounters a hardware error and returns a negative
error code such as -EPIPE, ret is implicitly promoted to size_t when
compared against size. This causes the negative error code to evaluate
as a large positive number, making the (ret > size) condition true.

This silently converts the hardware error into a success return value
and copies the unmodified buffer back, which could leave BPF programs
operating on uninitialized or stale data.

Fix this by casting size into ssize_t to return the actual negative
error code.

Link: https://lore.kernel.org/all/20260904130354.A79471F00A3D@smtp.kernel.org/
Fixes: 2b658c1c442e ("HID: bpf: prevent buffer overflow in hid_hw_request")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 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 b1de1dd0f21d..ece2c7c45ea6 100644
--- a/drivers/hid/bpf/hid_bpf_dispatch.c
+++ b/drivers/hid/bpf/hid_bpf_dispatch.c
@@ -453,7 +453,7 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
 					      (u64)(long)ctx,
 					      true); /* prevent infinite recursions */
 
-	if (ret > size)
+	if (ret > (ssize_t)size)
 		ret = size;
 	if (ret > 0)
 		memcpy(buf, dma_data, ret);

-- 
2.55.0