[PATCH bpf-next v2 1/2] HID: bpf: Fix hid_bpf_get_data() range check

[Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>]

hid_bpf_get_data() returns a pointer into the HID-BPF context data when
the caller-provided offset and size fit inside ctx->allocated_size.

The current check adds rdwr_buf_size and offset before comparing the
result against ctx->allocated_size. Since both values are unsigned, a
very large size can wrap the sum below ctx->allocated_size and make the
helper return a pointer even though the requested range is not contained
in the backing buffer.

Use a non-wrapping range check instead: reject offsets beyond the
allocation, then compare the requested size with the remaining bytes
after the offset.

Fixes: 658ee5a64fcf ("HID: bpf: allocate data memory for device_event BPF programs")
Signed-off-by: Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>
---
 drivers/hid/bpf/hid_bpf_dispatch.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
index d0130658091b0..09b45c40d84f0 100644
--- a/drivers/hid/bpf/hid_bpf_dispatch.c
+++ b/drivers/hid/bpf/hid_bpf_dispatch.c
@@ -299,7 +299,8 @@ hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t rdwr
 
 	ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx);
 
-	if (rdwr_buf_size + offset > ctx->allocated_size)
+	if (offset > ctx->allocated_size ||
+	    rdwr_buf_size > ctx->allocated_size - offset)
 		return NULL;
 
 	return ctx_kern->data + offset;
-- 
2.34.1