Am 17.03.2014 um 23:04 hat Max Reitz geschrieben:
> If qcow2_alloc_clusters() fails, new_offset and ret will both be
> negative after the fail label, thus passing the first if condition and
> subsequently resulting in a call of qcow2_free_clusters() with an
> invalid (negative) offset parameter. Fix this by introducing a new label
> "fail_free_cluster" which is only invoked if new_offset is indeed
> pointing to a newly allocated cluster that should be cleaned up by
> freeing it.
>
> While we're at it, clean up the whole fail path. qcow2_cache_put()
> should (and actually can) never fail, hence the return value can safely
> be ignored (aside from asserting that it indeed did not fail).
>
> Furthermore, there is no reason to give QCOW2_DISCARD_ALWAYS to
> qcow2_free_clusters(), a mere QCOW2_DISCARD_OTHER will suffice.
>
> Ultimately, rename the "fail" label to "done", as it is invoked both on
> failure and success.
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> Suggested-by: Laszlo Ersek <ler...@redhat.com>
> ---
> block/qcow2-refcount.c | 34 ++++++++++++++++++----------------
> 1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 3f2ed08..4a2df5f 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -1399,14 +1399,14 @@ static int64_t
> realloc_refcount_block(BlockDriverState *bs, int reftable_index,
> fprintf(stderr, "Could not allocate new cluster: %s\n",
> strerror(-new_offset));
> ret = new_offset;
> - goto fail;
> + goto done;
> }
>
> /* fetch current refcount block content */
> ret = qcow2_cache_get(bs, s->refcount_block_cache, offset,
> &refcount_block);
> if (ret < 0) {
> fprintf(stderr, "Could not fetch refcount block: %s\n",
> strerror(-ret));
> - goto fail;
> + goto fail_free_cluster;
> }
>
> /* new block has not yet been entered into refcount table, therefore it
> is
> @@ -1417,8 +1417,7 @@ static int64_t realloc_refcount_block(BlockDriverState
> *bs, int reftable_index,
> "check failed: %s\n", strerror(-ret));
> /* the image will be marked corrupt, so don't even attempt on freeing
> * the cluster */
> - new_offset = 0;
> - goto fail;
> + goto done;
> }
>
> /* write to new block */
> @@ -1426,7 +1425,7 @@ static int64_t realloc_refcount_block(BlockDriverState
> *bs, int reftable_index,
> s->cluster_sectors);
> if (ret < 0) {
> fprintf(stderr, "Could not write refcount block: %s\n",
> strerror(-ret));
> - goto fail;
> + goto fail_free_cluster;
> }
>
> /* update refcount table */
> @@ -1436,24 +1435,27 @@ static int64_t
> realloc_refcount_block(BlockDriverState *bs, int reftable_index,
> if (ret < 0) {
> fprintf(stderr, "Could not update refcount table: %s\n",
> strerror(-ret));
> - goto fail;
> + goto fail_free_cluster;
> }
>
> -fail:
> - if (new_offset && (ret < 0)) {
> - qcow2_free_clusters(bs, new_offset, s->cluster_size,
> - QCOW2_DISCARD_ALWAYS);
> - }
> + goto done;
I generally prefer an explicit ret = 0 in such places, so that we don't
have to rely on the next person adding new code before the goto to
understand the dependency here.
But it's correct code, so I won't block it because of this.
Kevin
