ivshmem: Check ivshmem_read() size argument

The third argument to the fd_read() callback implemented by
ivshmem_read() is the number of bytes, not a flags field.  Fix this and
check we received enough bytes before accessing the buffer pointer.

Cc: Cam Macdonell <cam@cs.ualberta.ca>
Reported-by: Sebastian Krahmer <krahmer@suse.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
[AF: Handle partial reads via FIFO]
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-stable@nongnu.org
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

(cherry picked from commit a2e9011b41)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/misc/ivshmem.c

@@ -24,6 +24,7 @@
 #include "migration/migration.h"
 #include "qapi/qmp/qerror.h"
 #include "qemu/event_notifier.h"
+#include "qemu/fifo8.h"
 #include "sysemu/char.h"
 
 #include <sys/mman.h>
@@ -73,6 +74,7 @@ typedef struct IVShmemState {
 
     CharDriverState **eventfd_chr;
     CharDriverState *server_chr;
+    Fifo8 incoming_fifo;
     MemoryRegion ivshmem_mmio;
 
     /* We might need to register the BAR before we actually have the memory.
@@ -420,14 +422,35 @@ static void increase_dynamic_storage(IVShmemState *s, int new_min_size) {
     }
 }
 
-static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
+static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
 {
     IVShmemState *s = opaque;
     int incoming_fd, tmp_fd;
     int guest_max_eventfd;
     long incoming_posn;
 
-    memcpy(&incoming_posn, buf, sizeof(long));
+    if (fifo8_is_empty(&s->incoming_fifo) && size == sizeof(incoming_posn)) {
+        memcpy(&incoming_posn, buf, size);
+    } else {
+        const uint8_t *p;
+        uint32_t num;
+
+        IVSHMEM_DPRINTF("short read of %d bytes\n", size);
+        num = MAX(size, sizeof(long) - fifo8_num_used(&s->incoming_fifo));
+        fifo8_push_all(&s->incoming_fifo, buf, num);
+        if (fifo8_num_used(&s->incoming_fifo) < sizeof(incoming_posn)) {
+            return;
+        }
+        size -= num;
+        buf += num;
+        p = fifo8_pop_buf(&s->incoming_fifo, sizeof(incoming_posn), &num);
+        g_assert(num == sizeof(incoming_posn));
+        memcpy(&incoming_posn, p, sizeof(incoming_posn));
+        if (size > 0) {
+            fifo8_push_all(&s->incoming_fifo, buf, size);
+        }
+    }
+
     /* pick off s->server_chr->msgfd and store it, posn should accompany msg */
     tmp_fd = qemu_chr_fe_get_msgfd(s->server_chr);
     IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
@@ -659,6 +682,8 @@ static int pci_ivshmem_init(PCIDevice *dev)
         s->ivshmem_size = ivshmem_get_size(s);
     }
 
+    fifo8_create(&s->incoming_fifo, sizeof(long));
+
     register_savevm(DEVICE(dev), "ivshmem", 0, 0, ivshmem_save, ivshmem_load,
                                                                         dev);
 
@@ -795,6 +820,7 @@ static void pci_ivshmem_uninit(PCIDevice *dev)
     memory_region_destroy(&s->ivshmem);
     memory_region_destroy(&s->bar);
     unregister_savevm(DEVICE(dev), "ivshmem", s);
+    fifo8_destroy(&s->incoming_fifo);
 }
 
 static Property ivshmem_properties[] = {