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 doesn't 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 it's 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.