AF_ALG interface not marking the end of the scatter-gather list

[Tom Lendacky <thomas.lendacky@amd.com>]

I was doing some testing of the CCP driver using the AF_ALG interface
and encountered a BUG_ON statement during scatter-gather DMA mapping.

In algif_skcipher.c, before submitting a request to the the Crypto API
the input sg list is not updated to mark the last valid sg entry of the
input data. So even if there is only a single valid sg entry, sg_nents
returns 127 (the initial value used when creating the sg table).

In the CCP driver, when making a call to dma_map_sg I supply the number
of entries as returned by sg_nents. During this call, the sg elements
that are not valid cause a BUG_ON statement to be hit.

I've worked around the issue in skcipher_recvmsg by marking the last
valid sg entry (sg_mark_end(sgl->sg + sgl->cur - 1)) just before the
call to ablkcipher_request_set_crypt and then unmarking the entry after
the return from af_alg_wait_for_completion (using sg_unmark_end).

Is this an appropriate/valid solution for this issue?  If so, I can
submit a patch with the fix in algif_skcipher and algif_hash.

Thanks,
Tom