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 checking for new_offset being positive instead.
While we're at it, clean up the whole fail path. qcow2_cache_put() 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. Signed-off-by: Max Reitz <[email protected]> Suggested-by: Laszlo Ersek <[email protected]> --- block/qcow2-refcount.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 6151148..b111319 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -1440,20 +1440,22 @@ static int64_t realloc_refcount_block(BlockDriverState *bs, int reftable_index, } fail: - if (new_offset && (ret < 0)) { - qcow2_free_clusters(bs, new_offset, s->cluster_size, - QCOW2_DISCARD_ALWAYS); - } 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) { + if (new_offset > 0) { + qcow2_free_clusters(bs, new_offset, s->cluster_size, + QCOW2_DISCARD_OTHER); + } return ret; } + return new_offset; } -- 1.9.0
