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/qmp/qerror.h"
  17 #include "qemu/main-loop.h"
  18
  19 struct RndRandom
  20 {
  21     RngBackend parent;
  22
  23     int fd;
  24     char *filename;
  25 };
  26
  27 /**
  28  * A simple and incomplete backend to request entropy from /dev/random.
  29  *
  30  * This backend exposes an additional "filename" property that can be used to
  31  * set the filename to use to open the backend.
  32  */
  33
  34 static void entropy_available(void *opaque)
  35 {
  36     RndRandom *s = RNG_RANDOM(opaque);
  37
  38     while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
  39         RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
  40         ssize_t len;
  41
  42         len = read(s->fd, req->data, req->size);
  43         if (len < 0 && errno == EAGAIN) {
  44             return;
  45         }
  46         g_assert(len != -1);
  47
  48         req->receive_entropy(req->opaque, req->data, len);
  49
  50         rng_backend_finalize_request(&s->parent, req);
  51     }
  52
  53     /* We've drained all requests, the fd handler can be reset. */
  54     qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
  55 }
  56
  57 static void rng_random_request_entropy(RngBackend *b, RngRequest *req)
  58 {
  59     RndRandom *s = RNG_RANDOM(b);
  60
  61     if (QSIMPLEQ_EMPTY(&s->parent.requests)) {
  62         /* If there are no pending requests yet, we need to
  63          * install our fd handler. */
  64         qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
  65     }
  66 }
  67
  68 static void rng_random_opened(RngBackend *b, Error **errp)
  69 {
  70     RndRandom *s = RNG_RANDOM(b);
  71
  72     if (s->filename == NULL) {
  73         error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
  74                    "filename", "a valid filename");
  75     } else {
  76         s->fd = qemu_open(s->filename, O_RDONLY | O_NONBLOCK);
  77         if (s->fd == -1) {
  78             error_setg_file_open(errp, errno, s->filename);
  79         }
  80     }
  81 }
  82
  83 static char *rng_random_get_filename(Object *obj, Error **errp)
  84 {
  85     RndRandom *s = RNG_RANDOM(obj);
  86
  87     return g_strdup(s->filename);
  88 }
  89
  90 static void rng_random_set_filename(Object *obj, const char *filename,
  91                                  Error **errp)
  92 {
  93     RngBackend *b = RNG_BACKEND(obj);
  94     RndRandom *s = RNG_RANDOM(obj);
  95
  96     if (b->opened) {
  97         error_setg(errp, QERR_PERMISSION_DENIED);
  98         return;
  99     }
 100
 101     g_free(s->filename);
 102     s->filename = g_strdup(filename);
 103 }
 104
 105 static void rng_random_init(Object *obj)
 106 {
 107     RndRandom *s = RNG_RANDOM(obj);
 108
 109     object_property_add_str(obj, "filename",
 110                             rng_random_get_filename,
 111                             rng_random_set_filename,
 112                             NULL);
 113
 114     s->filename = g_strdup("/dev/random");
 115     s->fd = -1;
 116 }
 117
 118 static void rng_random_finalize(Object *obj)
 119 {
 120     RndRandom *s = RNG_RANDOM(obj);
 121
 122     if (s->fd != -1) {
 123         qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
 124         qemu_close(s->fd);
 125     }
 126
 127     g_free(s->filename);
 128 }
 129
 130 static void rng_random_class_init(ObjectClass *klass, void *data)
 131 {
 132     RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
 133
 134     rbc->request_entropy = rng_random_request_entropy;
 135     rbc->opened = rng_random_opened;
 136 }
 137
 138 static const TypeInfo rng_random_info = {
 139     .name = TYPE_RNG_RANDOM,
 140     .parent = TYPE_RNG_BACKEND,
 141     .instance_size = sizeof(RndRandom),
 142     .class_init = rng_random_class_init,
 143     .instance_init = rng_random_init,
 144     .instance_finalize = rng_random_finalize,
 145 };
 146
 147 static void register_types(void)
 148 {
 149     type_register_static(&rng_random_info);
 150 }
 151
 152 type_init(register_types);