af_alg broken in 3.12

[Torsten Duwe <duwe@xxxxxx>]

Hi Herbert,

you sent a backport of 6de62f15b581f920ade22d758f4c338311c2f0d4 to be included
in the 3.12 branch (as b2a0707817d3dec83652bb460a7775613058ae), but this leaves
af_alg broken for unkeyed hash functions:

f382cd5ac26674877143fa7d9c0ea23c6640e706 (3.12 just before your commit) :

socket(PF_ALG, SOCK_SEQPACKET, 0)       = 3
bind(3, {sa_family=AF_ALG, sa_data="hash\0\0\0\0\0\0\0\0\0\0"}, 88) = 0
accept(3, 0, NULL)                      = 4
write(4, "abc", 3)                      = 3
read(4, "\220\1P\230<\322O\260\326\226?}(\341\177r", 16) = 16

and with b2a0707817d3dec83652bb460a7775613058ae applied:

socket(PF_ALG, SOCK_SEQPACKET, 0)       = 3
bind(3, {sa_family=AF_ALG, sa_data="hash\0\0\0\0\0\0\0\0\0\0"}, 88) = 0
accept(3, 0, NULL)                      = 4
write(4, "abc", 3)                      = -1 ENOKEY (Required key not available)
read(4, 0x7ffebeba0e30, 16)             = -1 ENOKEY (Required key not available)

Mainline has meanwhile seen many fixes to this change; can you suggest an elegant
and crisp backport for these as well?

TIA,
	Torsten

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/if_alg.h>
#include <errno.h>

int main(void)
{
  int opfd;
  int tfmfd;
  struct sockaddr_alg sa = {
    .salg_family = AF_ALG,
    .salg_type = "hash",
    .salg_name = "md5"
  };
  char buf[20];
  int i;

  tfmfd = socket(AF_ALG, SOCK_SEQPACKET, 0);

  bind(tfmfd, (struct sockaddr *)&sa, sizeof(sa));

  opfd = accept(tfmfd, NULL, 0);

  write(opfd, "abc", 3);
  if (read(opfd, buf, 16) == -1) {
    printf("ERROR: %d\n", errno);
    exit(-1);
  }

  for (i = 0; i < 16; i++) {
    printf("%02x", (unsigned char)buf[i]);
  }
  printf("\n");

  close(opfd);
  close(tfmfd);

  return 0;
}