CVE-2023-53778

In the Linux kernel, the following vulnerability has been resolved:

accel/qaic: Clean up integer overflow checking in map_user_pages()

The encode_dma() function has some validation on in_trans->size but it would be more clear to move those checks to find_and_map_user_pages().

The encode_dma() had two checks:

if (in_trans->addr + in_trans->size < in_trans->addr || !in_trans->size)
	return -EINVAL;

The in_trans->addr variable is the starting address. The in_trans->size variable is the total size of the transfer. The transfer can occur in parts and the resources->xferred_dma_size tracks how many bytes we have already transferred.

This patch introduces a new variable remaining which represents the amount we want to transfer (in_trans->size) minus the amount we have already transferred (resources->xferred_dma_size).

I have modified the check for if in_trans->size is zero to instead check if in_trans->size is less than resources->xferred_dma_size. If we have already transferred more bytes than in_trans->size then there are negative bytes remaining which doesnt make sense. If there are zero bytes remaining to be copied, just return success.

The check in encode_dma() checked that addr + size could not overflow and barring a driver bug that should work, but its easier to check if we do this in parts. First check that in_trans->addr + resources->xferred_dma_size is safe. Then check that xfer_start_addr + remaining is safe.

My final concern was that we are dealing with u64 values but on 32bit systems the kmalloc() function will truncate the sizes to 32 bits. So I calculated total = in_trans->size + offset_in_page(xfer_start_addr); and returned -EINVAL if it were >= SIZE_MAX. This will not affect 64bit systems.

Affected Software

References

• https://git.kernel.org/stable/c/96d3c1cadedb6ae2e8965e19cd12caa244afbd9c
• https://git.kernel.org/stable/c/d410a96e5cb8c1ec7049c83f2edcd8bbfaf5d9b3