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Re: [Qemu-devel] [PATCH v4 02/10] raw: Check byte range uniformly
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v4 02/10] raw: Check byte range uniformly |
Date: |
Mon, 14 May 2018 09:57:45 +0800 |
User-agent: |
Mutt/1.9.2 (2017-12-15) |
On Fri, 05/11 08:59, Eric Blake wrote:
> On 05/11/2018 07:08 AM, Fam Zheng wrote:
> > We don't verify the request range against s->size in the I/O callbacks
> > except for raw_co_pwritev. This is wrong (especially for
> > raw_co_pwrite_zeroes and raw_co_pdiscard), so fix them.
>
> Did you bother identifying how long the bug has been present (but read
> below, because I'm not sure there was even a bug)?
>
> CC: address@hidden
>
> >
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> > block/raw-format.c | 63
> > ++++++++++++++++++++++++++++++++----------------------
> > 1 file changed, 38 insertions(+), 25 deletions(-)
> >
> > diff --git a/block/raw-format.c b/block/raw-format.c
> > index a378547c99..803083f1a1 100644
> > --- a/block/raw-format.c
> > +++ b/block/raw-format.c
> > @@ -167,16 +167,36 @@ static void raw_reopen_abort(BDRVReopenState *state)
> > state->opaque = NULL;
> > }
> > +/* Check and adjust the offset, against 'offset' and 'size' options. */
> > +static inline int raw_adjust_offset(BlockDriverState *bs, uint64_t *offset,
> > + uint64_t bytes)
> > +{
> > + BDRVRawState *s = bs->opaque;
> > +
> > + if (s->has_size && (*offset > s->size || bytes > (s->size - *offset)))
> > {
> > + /* There's not enough space for the data. Don't write anything and
> > just
> > + * fail to prevent leaking out of the size specified in options. */
> > + return -ENOSPC;
> > + }
>
> Can this even trigger? The block layer should already be clamping requests
> according to the device's reported size, and we already report a smaller
> size according to s->size and s->offset. This could probably be an
> assertion instead.
There is the "write_beyond_eof" semantics in block layer, so the requested range
can escape the allowed here.
>
> > +
> > + if (*offset > UINT64_MAX - s->offset) {
> > + return -EINVAL;
>
> Should this be against INT64_MAX instead? After all, we really do use off_t
> (a 63-bit quantity, since it is signed), rather than uint64_t, as our
> maximum (theoretical) image size. But again, can it even trigger, or can it
> be an assertion?
>
> > + }
> > + *offset += s->offset;
> > +
> > + return 0;
> > +}
> > +
> > static int coroutine_fn raw_co_preadv(BlockDriverState *bs, uint64_t
> > offset,
> > uint64_t bytes, QEMUIOVector *qiov,
> > int flags)
> > {
> > - BDRVRawState *s = bs->opaque;
> > + int ret;
> > - if (offset > UINT64_MAX - s->offset) {
> > - return -EINVAL;
> > + ret = raw_adjust_offset(bs, &offset, bytes);
>
> If I'm right and we can assert instead of failing, then raw_adjust_offset()
> doesn't return failure. If I'm wrong, then there is now a code path where
> we can return ENOSPC on a read, which is unusual and probably wrong.
Yeah, EINVAL is the right value I think.
>
> > + if (ret) {
> > + return ret;
> > }
> > - offset += s->offset;
> > BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
> > return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
> > @@ -186,23 +206,11 @@ static int coroutine_fn
> > raw_co_pwritev(BlockDriverState *bs, uint64_t offset,
> > uint64_t bytes, QEMUIOVector *qiov,
> > int flags)
> > {
> > - BDRVRawState *s = bs->opaque;
> > void *buf = NULL;
> > BlockDriver *drv;
> > QEMUIOVector local_qiov;
> > int ret;
> > - if (s->has_size && (offset > s->size || bytes > (s->size - offset))) {
> > - /* There's not enough space for the data. Don't write anything and
> > just
> > - * fail to prevent leaking out of the size specified in options. */
> > - return -ENOSPC;
> > - }
> > -
> > - if (offset > UINT64_MAX - s->offset) {
> > - ret = -EINVAL;
> > - goto fail;
> > - }
>
> Okay, so you're just doing code refactoring; perhaps we could have done
> assertions here.
>
> > -
> > if (bs->probed && offset < BLOCK_PROBE_BUF_SIZE && bytes) {
> > /* Handling partial writes would be a pain - so we just
> > * require that guests have 512-byte request alignment if
> > @@ -237,7 +245,10 @@ static int coroutine_fn
> > raw_co_pwritev(BlockDriverState *bs, uint64_t offset,
> > qiov = &local_qiov;
> > }
> > - offset += s->offset;
> > + ret = raw_adjust_offset(bs, &offset, bytes);
> > + if (ret) {
> > + goto fail;
> > + }
> > BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
> > ret = bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
> > @@ -267,22 +278,24 @@ static int coroutine_fn
> > raw_co_pwrite_zeroes(BlockDriverState *bs,
> > int64_t offset, int bytes,
> > BdrvRequestFlags flags)
> > {
> > - BDRVRawState *s = bs->opaque;
> > - if (offset > UINT64_MAX - s->offset) {
> > - return -EINVAL;
> > + int ret;
> > +
> > + ret = raw_adjust_offset(bs, (uint64_t *)&offset, bytes);
> > + if (ret) {
> > + return ret;
> > }
> > - offset += s->offset;
>
> If I'm right and raw_adjust_offset() can't fail, then this didn't add any
> protection. If I'm wrong and it is possible to get the block layer to send
> a request beyond our advertised size, then this is indeed a bug fix worthy
> of being on the stable branch.
>
> > return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
> > }
> > static int coroutine_fn raw_co_pdiscard(BlockDriverState *bs,
> > int64_t offset, int bytes)
> > {
> > - BDRVRawState *s = bs->opaque;
> > - if (offset > UINT64_MAX - s->offset) {
> > - return -EINVAL;
> > + int ret;
> > +
> > + ret = raw_adjust_offset(bs, (uint64_t *)&offset, bytes);
> > + if (ret) {
> > + return ret;
> > }
> > - offset += s->offset;
> > return bdrv_co_pdiscard(bs->file->bs, offset, bytes);
> > }
> >
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc. +1-919-301-3266
> Virtualization: qemu.org | libvirt.org
Fam
- [Qemu-devel] [PATCH v4 00/10] qemu-img convert with copy offloading, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 01/10] block: Introduce API for copy offloading, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 02/10] raw: Check byte range uniformly, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 04/10] qcow2: Implement copy offloading, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 03/10] raw: Implement copy offloading, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 05/10] file-posix: Implement bdrv_co_copy_range, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 06/10] iscsi: Query and save device designator when opening, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 07/10] iscsi: Create and use iscsi_co_wait_for_task, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 08/10] iscsi: Implement copy offloading, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 09/10] block-backend: Add blk_co_copy_range, Fam Zheng, 2018/05/11
- [Qemu-devel] [PATCH v4 10/10] qemu-img: Convert with copy offloading, Fam Zheng, 2018/05/11