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
  20 struct RngRandom
  21 {
  22     RngBackend parent;
  23
  24     int fd;
  25     char *filename;
  26 };
  27
  28 /**
  29  * A simple and incomplete backend to request entropy from /dev/random.
  30  *
  31  * This backend exposes an additional "filename" property that can be used to
  32  * set the filename to use to open the backend.
  33  */
  34
  35 static void entropy_available(void *opaque)
  36 {
  37     RngRandom *s = RNG_RANDOM(opaque);
  38
  39     while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
  40         RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
  41         ssize_t len;
  42
  43         len = read(s->fd, req->data, req->size);
  44         if (len < 0 && errno == EAGAIN) {
  45             return;
  46         }
  47         g_assert(len != -1);
  48
  49         req->receive_entropy(req->opaque, req->data, len);
  50
  51         rng_backend_finalize_request(&s->parent, req);
  52     }
  53
  54     /* We've drained all requests, the fd handler can be reset. */
  55     qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
  56 }
  57
  58 static void rng_random_request_entropy(RngBackend *b, RngRequest *req)
  59 {
  60     RngRandom *s = RNG_RANDOM(b);
  61
  62     if (QSIMPLEQ_EMPTY(&s->parent.requests)) {
  63         /* If there are no pending requests yet, we need to
  64          * install our fd handler. */
  65         qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
  66     }
  67 }
  68
  69 static void rng_random_opened(RngBackend *b, Error **errp)
  70 {
  71     RngRandom *s = RNG_RANDOM(b);
  72
  73     if (s->filename == NULL) {
  74         error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
  75                    "filename", "a valid filename");
  76     } else {
  77         s->fd = qemu_open(s->filename, O_RDONLY | O_NONBLOCK);
  78         if (s->fd == -1) {
  79             error_setg_file_open(errp, errno, s->filename);
  80         }
  81     }
  82 }
  83
  84 static char *rng_random_get_filename(Object *obj, Error **errp)
  85 {
  86     RngRandom *s = RNG_RANDOM(obj);
  87
  88     return g_strdup(s->filename);
  89 }
  90
  91 static void rng_random_set_filename(Object *obj, const char *filename,
  92                                  Error **errp)
  93 {
  94     RngBackend *b = RNG_BACKEND(obj);
  95     RngRandom *s = RNG_RANDOM(obj);
  96
  97     if (b->opened) {
  98         error_setg(errp, QERR_PERMISSION_DENIED);
  99         return;
 100     }
 101
 102     g_free(s->filename);
 103     s->filename = g_strdup(filename);
 104 }
 105
 106 static void rng_random_init(Object *obj)
 107 {
 108     RngRandom *s = RNG_RANDOM(obj);
 109
 110     object_property_add_str(obj, "filename",
 111                             rng_random_get_filename,
 112                             rng_random_set_filename,
 113                             NULL);
 114
 115     s->filename = g_strdup("/dev/random");
 116     s->fd = -1;
 117 }
 118
 119 static void rng_random_finalize(Object *obj)
 120 {
 121     RngRandom *s = RNG_RANDOM(obj);
 122
 123     if (s->fd != -1) {
 124         qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
 125         qemu_close(s->fd);
 126     }
 127
 128     g_free(s->filename);
 129 }
 130
 131 static void rng_random_class_init(ObjectClass *klass, void *data)
 132 {
 133     RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
 134
 135     rbc->request_entropy = rng_random_request_entropy;
 136     rbc->opened = rng_random_opened;
 137 }
 138
 139 static const TypeInfo rng_random_info = {
 140     .name = TYPE_RNG_RANDOM,
 141     .parent = TYPE_RNG_BACKEND,
 142     .instance_size = sizeof(RngRandom),
 143     .class_init = rng_random_class_init,
 144     .instance_init = rng_random_init,
 145     .instance_finalize = rng_random_finalize,
 146 };
 147
 148 static void register_types(void)
 149 {
 150     type_register_static(&rng_random_info);
 151 }
 152
 153 type_init(register_types);