backends/rng-random.c

   1 /*
   2  * QEMU Random Number Generator Backend
   3  *
   4  * Copyright IBM, Corp. 2012
   5  *
   6  * Authors:
   7  *  Anthony Liguori   <aliguori@us.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  */
  12
  13 #include "qemu/osdep.h"
  14 #include "sysemu/rng-random.h"
  15 #include "sysemu/rng.h"
  16 #include "qapi/error.h"
  17 #include "qapi/qmp/qerror.h"
  18 #include "qemu/main-loop.h"
  19 #include "qemu/module.h"
  20
  21 struct RngRandom
  22 {
  23     RngBackend parent;
  24
  25     int fd;
  26     char *filename;
  27 };
  28
  29 /**
  30  * A simple and incomplete backend to request entropy from /dev/random.
  31  *
  32  * This backend exposes an additional "filename" property that can be used to
  33  * set the filename to use to open the backend.
  34  */
  35
  36 static void entropy_available(void *opaque)
  37 {
  38     RngRandom *s = RNG_RANDOM(opaque);
  39
  40     while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
  41         RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
  42         ssize_t len;
  43
  44         len = read(s->fd, req->data, req->size);
  45         if (len < 0 && errno == EAGAIN) {
  46             return;
  47         }
  48         g_assert(len != -1);
  49
  50         req->receive_entropy(req->opaque, req->data, len);
  51
  52         rng_backend_finalize_request(&s->parent, req);
  53     }
  54
  55     /* We've drained all requests, the fd handler can be reset. */
  56     qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
  57 }
  58
  59 static void rng_random_request_entropy(RngBackend *b, RngRequest *req)
  60 {
  61     RngRandom *s = RNG_RANDOM(b);
  62
  63     if (QSIMPLEQ_EMPTY(&s->parent.requests)) {
  64         /* If there are no pending requests yet, we need to
  65          * install our fd handler. */
  66         qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
  67     }
  68 }
  69
  70 static void rng_random_opened(RngBackend *b, Error **errp)
  71 {
  72     RngRandom *s = RNG_RANDOM(b);
  73
  74     if (s->filename == NULL) {
  75         error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
  76                    "filename", "a valid filename");
  77     } else {
  78         s->fd = qemu_open(s->filename, O_RDONLY | O_NONBLOCK, errp);
  79     }
  80 }
  81
  82 static char *rng_random_get_filename(Object *obj, Error **errp)
  83 {
  84     RngRandom *s = RNG_RANDOM(obj);
  85
  86     return g_strdup(s->filename);
  87 }
  88
  89 static void rng_random_set_filename(Object *obj, const char *filename,
  90                                  Error **errp)
  91 {
  92     RngBackend *b = RNG_BACKEND(obj);
  93     RngRandom *s = RNG_RANDOM(obj);
  94
  95     if (b->opened) {
  96         error_setg(errp, "Property 'filename' can no longer be set");
  97         return;
  98     }
  99
 100     g_free(s->filename);
 101     s->filename = g_strdup(filename);
 102 }
 103
 104 static void rng_random_init(Object *obj)
 105 {
 106     RngRandom *s = RNG_RANDOM(obj);
 107
 108     s->filename = g_strdup("/dev/urandom");
 109     s->fd = -1;
 110 }
 111
 112 static void rng_random_finalize(Object *obj)
 113 {
 114     RngRandom *s = RNG_RANDOM(obj);
 115
 116     if (s->fd != -1) {
 117         qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
 118         qemu_close(s->fd);
 119     }
 120
 121     g_free(s->filename);
 122 }
 123
 124 static void rng_random_class_init(ObjectClass *klass, void *data)
 125 {
 126     RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
 127
 128     rbc->request_entropy = rng_random_request_entropy;
 129     rbc->opened = rng_random_opened;
 130     object_class_property_add_str(klass, "filename",
 131                                   rng_random_get_filename,
 132                                   rng_random_set_filename);
 133
 134 }
 135
 136 static const TypeInfo rng_random_info = {
 137     .name = TYPE_RNG_RANDOM,
 138     .parent = TYPE_RNG_BACKEND,
 139     .instance_size = sizeof(RngRandom),
 140     .class_init = rng_random_class_init,
 141     .instance_init = rng_random_init,
 142     .instance_finalize = rng_random_finalize,
 143 };
 144
 145 static void register_types(void)
 146 {
 147     type_register_static(&rng_random_info);
 148 }
 149
 150 type_init(register_types);