blk_aio_prwv() now takes a void pointer and the coroutine functions have been
modified to cast it into QEMUIOVector if needed. It does not use an union in
BlkRwCo since this leads to code - blk_aio_prwv() would have to write to the
void pointer member, but coroutines would sometimes read the QEMUIOVector
member. Paolo also suggested not using a union.
Note that a similar issue exists in blk_ioctl()/blk_ioctl_entry()/blk_prw()
where blk_prw() always creates the QEMUIOVector even if
blk_ioctl()/blk_ioctl_entry() does not need a QEMUIOVector. This will need to
be fixed separately to keep it consistent with the AIO path.
> On Nov 23, 2017, at 8:55 AM, Deepa Srinivasan <deepa.sriniva...@oracle.com>
> wrote:
>
> Starting qemu with the following arguments causes qemu to segfault:
> ... -device lsi,id=lsi0 -drive file=iscsi:<...>,format=raw,if=none,node-name=
> iscsi1 -device scsi-block,bus=lsi0.0,id=<...>,drive=iscsi1
>
> This patch fixes blk_aio_ioctl() so it does not pass stack addresses to
> blk_aio_ioctl_entry() which may be invoked after blk_aio_ioctl() returns. More
> details about the bug follow.
>
> blk_aio_ioctl() invokes blk_aio_prwv() with blk_aio_ioctl_entry as the
> coroutine parameter. blk_aio_prwv() ultimately calls aio_co_enter().
>
> When blk_aio_ioctl() is executed from within a coroutine context (e.g.
> iscsi_bh_cb()), aio_co_enter() adds the coroutine (blk_aio_ioctl_entry) to
> the current coroutine's wakeup queue. blk_aio_ioctl() then returns.
>
> When blk_aio_ioctl_entry() executes later, it accesses an invalid pointer:
> ....
> BlkRwCo *rwco = &acb->rwco;
>
> rwco->ret = blk_co_ioctl(rwco->blk, rwco->offset,
> rwco->qiov->iov[0].iov_base); <--- qiov is
> invalid here
> ...
>
> In the case when blk_aio_ioctl() is called from a non-coroutine context,
> blk_aio_ioctl_entry() executes immediately. But if bdrv_co_ioctl() calls
> qemu_coroutine_yield(), blk_aio_ioctl() will return. When the coroutine
> execution is complete, control returns to blk_aio_ioctl_entry() after the call
> to blk_co_ioctl(). There is no invalid reference after this point, but the
> function is still holding on to invalid pointers.
>
> The fix is to change blk_aio_prwv() to accept a void pointer for the IO buffer
> rather than a QEMUIOVector. blk_aio_prwv() passes this through in BlkRwCo and
> the
> coroutine function casts it to QEMUIOVector or uses the void pointer directly.
>
> Signed-off-by: Deepa Srinivasan <deepa.sriniva...@oracle.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Reviewed-by: Mark Kanda <mark.ka...@oracle.com>
> ---
> block/block-backend.c | 51 +++++++++++++++++++++++++--------------------------
> 1 file changed, 25 insertions(+), 26 deletions(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index baef8e7..2d0d9b6 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1140,7 +1140,7 @@ int coroutine_fn blk_co_pwritev(BlockBackend *blk,
> int64_t offset,
> typedef struct BlkRwCo {
> BlockBackend *blk;
> int64_t offset;
> - QEMUIOVector *qiov;
> + void *iobuf;
> int ret;
> BdrvRequestFlags flags;
> } BlkRwCo;
> @@ -1148,17 +1148,19 @@ typedef struct BlkRwCo {
> static void blk_read_entry(void *opaque)
> {
> BlkRwCo *rwco = opaque;
> + QEMUIOVector *qiov = rwco->iobuf;
>
> - rwco->ret = blk_co_preadv(rwco->blk, rwco->offset, rwco->qiov->size,
> - rwco->qiov, rwco->flags);
> + rwco->ret = blk_co_preadv(rwco->blk, rwco->offset, qiov->size,
> + qiov, rwco->flags);
> }
>
> static void blk_write_entry(void *opaque)
> {
> BlkRwCo *rwco = opaque;
> + QEMUIOVector *qiov = rwco->iobuf;
>
> - rwco->ret = blk_co_pwritev(rwco->blk, rwco->offset, rwco->qiov->size,
> - rwco->qiov, rwco->flags);
> + rwco->ret = blk_co_pwritev(rwco->blk, rwco->offset, qiov->size,
> + qiov, rwco->flags);
> }
>
> static int blk_prw(BlockBackend *blk, int64_t offset, uint8_t *buf,
> @@ -1178,7 +1180,7 @@ static int blk_prw(BlockBackend *blk, int64_t offset,
> uint8_t *buf,
> rwco = (BlkRwCo) {
> .blk = blk,
> .offset = offset,
> - .qiov = &qiov,
> + .iobuf = &qiov,
> .flags = flags,
> .ret = NOT_DONE,
> };
> @@ -1275,7 +1277,7 @@ static void blk_aio_complete_bh(void *opaque)
> }
>
> static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
> - QEMUIOVector *qiov, CoroutineEntry co_entry,
> + void *iobuf, CoroutineEntry co_entry,
> BdrvRequestFlags flags,
> BlockCompletionFunc *cb, void *opaque)
> {
> @@ -1287,7 +1289,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk,
> int64_t offset, int bytes,
> acb->rwco = (BlkRwCo) {
> .blk = blk,
> .offset = offset,
> - .qiov = qiov,
> + .iobuf = iobuf,
> .flags = flags,
> .ret = NOT_DONE,
> };
> @@ -1310,10 +1312,11 @@ static void blk_aio_read_entry(void *opaque)
> {
> BlkAioEmAIOCB *acb = opaque;
> BlkRwCo *rwco = &acb->rwco;
> + QEMUIOVector *qiov = rwco->iobuf;
>
> - assert(rwco->qiov->size == acb->bytes);
> + assert(qiov->size == acb->bytes);
> rwco->ret = blk_co_preadv(rwco->blk, rwco->offset, acb->bytes,
> - rwco->qiov, rwco->flags);
> + qiov, rwco->flags);
> blk_aio_complete(acb);
> }
>
> @@ -1321,10 +1324,11 @@ static void blk_aio_write_entry(void *opaque)
> {
> BlkAioEmAIOCB *acb = opaque;
> BlkRwCo *rwco = &acb->rwco;
> + QEMUIOVector *qiov = rwco->iobuf;
>
> - assert(!rwco->qiov || rwco->qiov->size == acb->bytes);
> + assert(!qiov || qiov->size == acb->bytes);
> rwco->ret = blk_co_pwritev(rwco->blk, rwco->offset, acb->bytes,
> - rwco->qiov, rwco->flags);
> + qiov, rwco->flags);
> blk_aio_complete(acb);
> }
>
> @@ -1453,8 +1457,10 @@ int blk_co_ioctl(BlockBackend *blk, unsigned long int
> req, void *buf)
> static void blk_ioctl_entry(void *opaque)
> {
> BlkRwCo *rwco = opaque;
> + QEMUIOVector *qiov = rwco->iobuf;
> +
> rwco->ret = blk_co_ioctl(rwco->blk, rwco->offset,
> - rwco->qiov->iov[0].iov_base);
> + qiov->iov[0].iov_base);
> }
>
> int blk_ioctl(BlockBackend *blk, unsigned long int req, void *buf)
> @@ -1467,24 +1473,15 @@ static void blk_aio_ioctl_entry(void *opaque)
> BlkAioEmAIOCB *acb = opaque;
> BlkRwCo *rwco = &acb->rwco;
>
> - rwco->ret = blk_co_ioctl(rwco->blk, rwco->offset,
> - rwco->qiov->iov[0].iov_base);
> + rwco->ret = blk_co_ioctl(rwco->blk, rwco->offset, rwco->iobuf);
> +
> blk_aio_complete(acb);
> }
>
> BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, void *buf,
> BlockCompletionFunc *cb, void *opaque)
> {
> - QEMUIOVector qiov;
> - struct iovec iov;
> -
> - iov = (struct iovec) {
> - .iov_base = buf,
> - .iov_len = 0,
> - };
> - qemu_iovec_init_external(&qiov, &iov, 1);
> -
> - return blk_aio_prwv(blk, req, 0, &qiov, blk_aio_ioctl_entry, 0, cb,
> opaque);
> + return blk_aio_prwv(blk, req, 0, buf, blk_aio_ioctl_entry, 0, cb,
> opaque);
> }
>
> int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int bytes)
> @@ -1900,7 +1897,9 @@ int blk_truncate(BlockBackend *blk, int64_t offset,
> PreallocMode prealloc,
> static void blk_pdiscard_entry(void *opaque)
> {
> BlkRwCo *rwco = opaque;
> - rwco->ret = blk_co_pdiscard(rwco->blk, rwco->offset, rwco->qiov->size);
> + QEMUIOVector *qiov = rwco->iobuf;
> +
> + rwco->ret = blk_co_pdiscard(rwco->blk, rwco->offset, qiov->size);
> }
>
> int blk_pdiscard(BlockBackend *blk, int64_t offset, int bytes)
> --
> 2.7.4
>
>
