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libvhost-user: fix crash when rings aren't ready 

Calling libvhost-user functions like vu_queue_get_avail_bytes() when the
queue doesn't yet have addresses will result in the crashes like the
following:

Program received signal SIGSEGV, Segmentation fault.
0x000055c414112ce4 in vring_avail_idx (vq=0x55c41582fd68, vq=0x55c41582fd68)
    at /home/dgilbert/git/qemu/contrib/libvhost-user/libvhost-user.c:940
940            vq->shadow_avail_idx = vq->vring.avail->idx;
(gdb) p vq
$1 = (VuVirtq *) 0x55c41582fd68
(gdb) p vq->vring
$2 = {num = 0, desc = 0x0, avail = 0x0, used = 0x0, log_guest_addr = 0, flags = 0}

    at /home/dgilbert/git/qemu/contrib/libvhost-user/libvhost-user.c:940
No locals.
    at /home/dgilbert/git/qemu/contrib/libvhost-user/libvhost-user.c:960
        num_heads = <optimized out>
    out_bytes=out_bytes@entry=0x7fffd035d7c4, max_in_bytes=max_in_bytes@entry=0,
    max_out_bytes=max_out_bytes@entry=0) at /home/dgilbert/git/qemu/contrib/libvhost-user/libvhost-user.c:1034

Add a pre-condition checks on vring.avail before accessing it.

Fix documentation and return type of vu_queue_empty() while at it.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
master
Marc-André Lureau 2017-05-03 20:54:12 +04:00 committed by Michael S. Tsirkin
parent 60cd11024f
commit 640601c7cb
2 changed files with 23 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
contrib/libvhost-user/libvhost-user.c
View File

@ -1031,6 +1031,11 @@ vu_queue_get_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned int *in_bytes,
idx = vq->last_avail_idx;
total_bufs = in_total = out_total = 0;
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
goto done;
}
while ((rc = virtqueue_num_heads(dev, vq, idx)) > 0) {
unsigned int max, num_bufs, indirect = 0;
struct vring_desc *desc;
@ -1121,11 +1126,16 @@ vu_queue_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned int in_bytes,
/* Fetch avail_idx from VQ memory only when we really need to know if
* guest has added some buffers. */
int
bool
vu_queue_empty(VuDev *dev, VuVirtq *vq)
{
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
return true;
}
if (vq->shadow_avail_idx != vq->last_avail_idx) {
return 0;
return false;
}
return vring_avail_idx(vq) == vq->last_avail_idx;
@ -1174,7 +1184,8 @@ vring_notify(VuDev *dev, VuVirtq *vq)
void
vu_queue_notify(VuDev *dev, VuVirtq *vq)
{
if (unlikely(dev->broken)) {
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
return;
}
@ -1291,7 +1302,8 @@ vu_queue_pop(VuDev *dev, VuVirtq *vq, size_t sz)
struct vring_desc *desc;
int rc;
if (unlikely(dev->broken)) {
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
return NULL;
}
@ -1445,7 +1457,8 @@ vu_queue_fill(VuDev *dev, VuVirtq *vq,
{
struct vring_used_elem uelem;
if (unlikely(dev->broken)) {
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
return;
}
@ -1474,7 +1487,8 @@ vu_queue_flush(VuDev *dev, VuVirtq *vq, unsigned int count)
{
uint16_t old, new;
if (unlikely(dev->broken)) {
if (unlikely(dev->broken) ||
unlikely(!vq->vring.avail)) {
return;
}

6
contrib/libvhost-user/libvhost-user.h
View File

@ -327,13 +327,13 @@ void vu_queue_set_notification(VuDev *dev, VuVirtq *vq, int enable);
bool vu_queue_enabled(VuDev *dev, VuVirtq *vq);
/**
* vu_queue_enabled:
* vu_queue_empty:
* @dev: a VuDev context
* @vq: a VuVirtq queue
*
* Returns: whether the queue is empty.
* Returns: true if the queue is empty or not ready.
*/
int vu_queue_empty(VuDev *dev, VuVirtq *vq);
bool vu_queue_empty(VuDev *dev, VuVirtq *vq);
/**
* vu_queue_notify: