On 03/17/14 23:04, Max Reitz wrote: > 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; > + > +fail_free_cluster: > + qcow2_free_clusters(bs, new_offset, s->cluster_size, > QCOW2_DISCARD_OTHER); > + > +done: > if (refcount_block) { > - if (ret < 0) { > - qcow2_cache_put(bs, s->refcount_block_cache, &refcount_block); > - } else { > - ret = qcow2_cache_put(bs, s->refcount_block_cache, > &refcount_block); > - } > + /* This should never fail, as it would only do so if the given > refcount > + * block cannot be found in the cache. As this is impossible as long > as > + * there are no bugs, assert the success. */ > + int tmp = qcow2_cache_put(bs, s->refcount_block_cache, > &refcount_block); > + assert(tmp == 0); > } > + > if (ret < 0) { > return ret; > } > + > return new_offset; > } > >
I liked the other version better. Especially crossing the trajectories of the gotos (where "new_offset" used to be zeroed) makes me want to avert my eyes. However, I've obsessed enough; the code seems correct. Reviewed-by: Laszlo Ersek <ler...@redhat.com> Thanks! Laszlo