scsi: storvsc: Fix swiotlb bounce buffer leak in confidential VM

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: scsi: storvsc: Fix swiotlb bounce buffer leak in confidential VM storvsc_queuecommand() maps the scatter/gather list using scsi_dma_map(), which in a confidential VM allocates swiotlb bounce buffers. If the I/O submission fails in storvsc_do_io(), the I/O is typically retried by higher level code, but the bounce buffer memory is never freed. The mostly like cause of I/O submission failure is a full VMBus channel ring buffer, which is not uncommon under high I/O loads. Eventually enough bounce buffer memory leaks that the confidential VM can't do any I/O. The same problem can arise in a non-confidential VM with kernel boot parameter swiotlb=force. Fix this by doing scsi_dma_unmap() in the case of an I/O submission error, which frees the bounce buffer memory.

References

• https://git.kernel.org/stable/c/87c71e88f6a6619ffb1ff88f84dff48ef6d57adb
• https://git.kernel.org/stable/c/67ff3d0a49f3d445c3922e30a54e03c161da561e