Commit c060332c authored by Deepa Srinivasan's avatar Deepa Srinivasan Committed by Stefan Hajnoczi
Browse files

block: Fix qemu crash when using scsi-block 



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: default avatarDeepa Srinivasan <deepa.srinivasan@oracle.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: default avatarMark Kanda <mark.kanda@oracle.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 0ab4537f

block/block-backend.c

+25 −26
Original line number Diff line number Diff line
@@ -1150,7 +1150,7 @@ 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;
@@ -1158,17 +1158,19 @@ 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,
@@ -1188,7 +1190,7 @@ 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,

    };
@@ -1296,7 +1298,7 @@ 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)

{
@@ -1308,7 +1310,7 @@ 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,

    };
@@ -1331,10 +1333,11 @@ 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);

}
@@ -1342,10 +1345,11 @@ 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);

}
@@ -1474,8 +1478,10 @@ 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)
@@ -1488,24 +1494,15 @@ 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)
@@ -1949,7 +1946,9 @@ 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)