From b106ad9185f35fc4ad669555ad0e79e276083bd7 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Fri, 28 Mar 2014 18:06:31 +0100 Subject: qcow2: Don't rely on free_cluster_index in alloc_refcount_block() (CVE-2014-0147) free_cluster_index is only correct if update_refcount() was called from an allocation function, and even there it's brittle because it's used to protect unfinished allocations which still have a refcount of 0 - if it moves in the wrong place, the unfinished allocation can be corrupted. So not using it any more seems to be a good idea. Instead, use the first requested cluster to do the calculations. Return -EAGAIN if unfinished allocations could become invalid and let the caller restart its search for some free clusters. The context of creating a snapsnot is one situation where update_refcount() is called outside of a cluster allocation. For this case, the change fixes a buffer overflow if a cluster is referenced in an L2 table that cannot be represented by an existing refcount block. (new_table[refcount_table_index] was out of bounds) [Bump the qemu-iotests 026 refblock_alloc.write leak count from 10 to 11. --Stefan] Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz Signed-off-by: Stefan Hajnoczi --- block/qcow2-refcount.c | 72 ++++++++++++++++++++++++++------------------------ 1 file changed, 37 insertions(+), 35 deletions(-) (limited to 'block/qcow2-refcount.c') diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index e3c7ecd..220b322 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -194,10 +194,11 @@ static int alloc_refcount_block(BlockDriverState *bs, * they can describe them themselves. * * - We need to consider that at this point we are inside update_refcounts - * and doing the initial refcount increase. This means that some clusters - * have already been allocated by the caller, but their refcount isn't - * accurate yet. free_cluster_index tells us where this allocation ends - * as long as we don't overwrite it by freeing clusters. + * and potentially doing an initial refcount increase. This means that + * some clusters have already been allocated by the caller, but their + * refcount isn't accurate yet. If we allocate clusters for metadata, we + * need to return -EAGAIN to signal the caller that it needs to restart + * the search for free clusters. * * - alloc_clusters_noref and qcow2_free_clusters may load a different * refcount block into the cache @@ -282,7 +283,10 @@ static int alloc_refcount_block(BlockDriverState *bs, } s->refcount_table[refcount_table_index] = new_block; - return 0; + + /* The new refcount block may be where the caller intended to put its + * data, so let it restart the search. */ + return -EAGAIN; } ret = qcow2_cache_put(bs, s->refcount_block_cache, (void**) refcount_block); @@ -305,8 +309,7 @@ static int alloc_refcount_block(BlockDriverState *bs, /* Calculate the number of refcount blocks needed so far */ uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT); - uint64_t blocks_used = (s->free_cluster_index + - refcount_block_clusters - 1) / refcount_block_clusters; + uint64_t blocks_used = DIV_ROUND_UP(cluster_index, refcount_block_clusters); /* And now we need at least one block more for the new metadata */ uint64_t table_size = next_refcount_table_size(s, blocks_used + 1); @@ -339,8 +342,6 @@ static int alloc_refcount_block(BlockDriverState *bs, uint16_t *new_blocks = g_malloc0(blocks_clusters * s->cluster_size); uint64_t *new_table = g_malloc0(table_size * sizeof(uint64_t)); - assert(meta_offset >= (s->free_cluster_index * s->cluster_size)); - /* Fill the new refcount table */ memcpy(new_table, s->refcount_table, s->refcount_table_size * sizeof(uint64_t)); @@ -403,18 +404,19 @@ static int alloc_refcount_block(BlockDriverState *bs, s->refcount_table_size = table_size; s->refcount_table_offset = table_offset; - /* Free old table. Remember, we must not change free_cluster_index */ - uint64_t old_free_cluster_index = s->free_cluster_index; + /* Free old table. */ qcow2_free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t), QCOW2_DISCARD_OTHER); - s->free_cluster_index = old_free_cluster_index; ret = load_refcount_block(bs, new_block, (void**) refcount_block); if (ret < 0) { return ret; } - return 0; + /* If we were trying to do the initial refcount update for some cluster + * allocation, we might have used the same clusters to store newly + * allocated metadata. Make the caller search some new space. */ + return -EAGAIN; fail_table: g_free(new_table); @@ -660,12 +662,15 @@ int64_t qcow2_alloc_clusters(BlockDriverState *bs, int64_t size) int ret; BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC); - offset = alloc_clusters_noref(bs, size); - if (offset < 0) { - return offset; - } + do { + offset = alloc_clusters_noref(bs, size); + if (offset < 0) { + return offset; + } + + ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER); + } while (ret == -EAGAIN); - ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER); if (ret < 0) { return ret; } @@ -678,7 +683,6 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset, { BDRVQcowState *s = bs->opaque; uint64_t cluster_index; - uint64_t old_free_cluster_index; uint64_t i; int refcount, ret; @@ -687,30 +691,28 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset, return 0; } - /* Check how many clusters there are free */ - cluster_index = offset >> s->cluster_bits; - for(i = 0; i < nb_clusters; i++) { - refcount = get_refcount(bs, cluster_index++); + do { + /* Check how many clusters there are free */ + cluster_index = offset >> s->cluster_bits; + for(i = 0; i < nb_clusters; i++) { + refcount = get_refcount(bs, cluster_index++); - if (refcount < 0) { - return refcount; - } else if (refcount != 0) { - break; + if (refcount < 0) { + return refcount; + } else if (refcount != 0) { + break; + } } - } - /* And then allocate them */ - old_free_cluster_index = s->free_cluster_index; - s->free_cluster_index = cluster_index + i; + /* And then allocate them */ + ret = update_refcount(bs, offset, i << s->cluster_bits, 1, + QCOW2_DISCARD_NEVER); + } while (ret == -EAGAIN); - ret = update_refcount(bs, offset, i << s->cluster_bits, 1, - QCOW2_DISCARD_NEVER); if (ret < 0) { return ret; } - s->free_cluster_index = old_free_cluster_index; - return i; } -- cgit v1.1