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From a2b10eec76a72aa7fe63e797181b93f69de9600e Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Tue, 25 Mar 2014 14:23:34 +0100
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Subject: [PATCH 27/49] qcow2: Don't rely on free_cluster_index in alloc_refcount_block() (CVE-2014-0147)
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <1395753835-7591-28-git-send-email-kwolf@redhat.com>
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Patchwork-id: n/a
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O-Subject: [virt-devel] [EMBARGOED RHEL-7.0 qemu-kvm PATCH 27/48] qcow2: Don't rely on free_cluster_index in alloc_refcount_block() (CVE-2014-0147)
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Bugzilla: 1079339
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RH-Acked-by: Jeff Cody <jcody@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1079339
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Upstream status: Embargoed
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free_cluster_index is only correct if update_refcount() was called from
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an allocation function, and even there it's brittle because it's used to
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protect unfinished allocations which still have a refcount of 0 - if it
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moves in the wrong place, the unfinished allocation can be corrupted.
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So not using it any more seems to be a good idea. Instead, use the
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first requested cluster to do the calculations. Return -EAGAIN if
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unfinished allocations could become invalid and let the caller restart
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its search for some free clusters.
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The context of creating a snapsnot is one situation where
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update_refcount() is called outside of a cluster allocation. For this
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case, the change fixes a buffer overflow if a cluster is referenced in
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an L2 table that cannot be represented by an existing refcount block.
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(new_table[refcount_table_index] was out of bounds)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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---
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 block/qcow2-refcount.c     |   74 ++++++++++++++++++++++---------------------
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 block/qcow2.c              |    7 ++--
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 tests/qemu-iotests/044.out |    2 +-
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 tests/qemu-iotests/080     |   11 ++++++
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 tests/qemu-iotests/080.out |    7 ++++
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 5 files changed, 61 insertions(+), 40 deletions(-)
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diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
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index 13ea5f7..54bcbd1 100644
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--- a/block/qcow2-refcount.c
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+++ b/block/qcow2-refcount.c
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@@ -193,10 +193,11 @@ static int alloc_refcount_block(BlockDriverState *bs,
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      *   they can describe them themselves.
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      *
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      * - We need to consider that at this point we are inside update_refcounts
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-     *   and doing the initial refcount increase. This means that some clusters
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-     *   have already been allocated by the caller, but their refcount isn't
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-     *   accurate yet. free_cluster_index tells us where this allocation ends
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-     *   as long as we don't overwrite it by freeing clusters.
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+     *   and potentially doing an initial refcount increase. This means that
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+     *   some clusters have already been allocated by the caller, but their
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+     *   refcount isn't accurate yet. If we allocate clusters for metadata, we
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+     *   need to return -EAGAIN to signal the caller that it needs to restart
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+     *   the search for free clusters.
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      *
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      * - alloc_clusters_noref and qcow2_free_clusters may load a different
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      *   refcount block into the cache
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@@ -281,7 +282,10 @@ static int alloc_refcount_block(BlockDriverState *bs,
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         }
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         s->refcount_table[refcount_table_index] = new_block;
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-        return 0;
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+
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+        /* The new refcount block may be where the caller intended to put its
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+         * data, so let it restart the search. */
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+        return -EAGAIN;
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     }
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     ret = qcow2_cache_put(bs, s->refcount_block_cache, (void**) refcount_block);
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@@ -304,8 +308,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
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     /* Calculate the number of refcount blocks needed so far */
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     uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT);
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-    uint64_t blocks_used = (s->free_cluster_index +
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-        refcount_block_clusters - 1) / refcount_block_clusters;
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+    uint64_t blocks_used = DIV_ROUND_UP(cluster_index, refcount_block_clusters);
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     /* And now we need at least one block more for the new metadata */
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     uint64_t table_size = next_refcount_table_size(s, blocks_used + 1);
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@@ -338,8 +341,6 @@ static int alloc_refcount_block(BlockDriverState *bs,
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     uint16_t *new_blocks = g_malloc0(blocks_clusters * s->cluster_size);
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     uint64_t *new_table = g_malloc0(table_size * sizeof(uint64_t));
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-    assert(meta_offset >= (s->free_cluster_index * s->cluster_size));
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-
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     /* Fill the new refcount table */
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     memcpy(new_table, s->refcount_table,
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         s->refcount_table_size * sizeof(uint64_t));
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@@ -402,18 +403,19 @@ static int alloc_refcount_block(BlockDriverState *bs,
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     s->refcount_table_size = table_size;
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     s->refcount_table_offset = table_offset;
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-    /* Free old table. Remember, we must not change free_cluster_index */
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-    uint64_t old_free_cluster_index = s->free_cluster_index;
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+    /* Free old table. */
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     qcow2_free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t),
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                         QCOW2_DISCARD_OTHER);
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-    s->free_cluster_index = old_free_cluster_index;
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     ret = load_refcount_block(bs, new_block, (void**) refcount_block);
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     if (ret < 0) {
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         return ret;
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     }
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-    return 0;
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+    /* If we were trying to do the initial refcount update for some cluster
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+     * allocation, we might have used the same clusters to store newly
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+     * allocated metadata. Make the caller search some new space. */
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+    return -EAGAIN;
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 fail_table:
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     g_free(new_table);
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@@ -659,12 +661,15 @@ int64_t qcow2_alloc_clusters(BlockDriverState *bs, int64_t size)
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     int ret;
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     BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC);
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-    offset = alloc_clusters_noref(bs, size);
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-    if (offset < 0) {
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-        return offset;
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-    }
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+    do {
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+        offset = alloc_clusters_noref(bs, size);
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+        if (offset < 0) {
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+            return offset;
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+        }
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+
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+        ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER);
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+    } while (ret == -EAGAIN);
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-    ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER);
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     if (ret < 0) {
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         return ret;
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     }
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@@ -677,7 +682,6 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset,
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 {
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     BDRVQcowState *s = bs->opaque;
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     uint64_t cluster_index;
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-    uint64_t old_free_cluster_index;
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     uint64_t i;
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     int refcount, ret;
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@@ -686,30 +690,28 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset,
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         return 0;
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     }
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-    /* Check how many clusters there are free */
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-    cluster_index = offset >> s->cluster_bits;
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-    for(i = 0; i < nb_clusters; i++) {
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-        refcount = get_refcount(bs, cluster_index++);
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+    do {
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+        /* Check how many clusters there are free */
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+        cluster_index = offset >> s->cluster_bits;
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+        for(i = 0; i < nb_clusters; i++) {
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+            refcount = get_refcount(bs, cluster_index++);
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-        if (refcount < 0) {
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-            return refcount;
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-        } else if (refcount != 0) {
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-            break;
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+            if (refcount < 0) {
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+                return refcount;
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+            } else if (refcount != 0) {
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+                break;
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+            }
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         }
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-    }
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-    /* And then allocate them */
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-    old_free_cluster_index = s->free_cluster_index;
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-    s->free_cluster_index = cluster_index + i;
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+        /* And then allocate them */
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+        ret = update_refcount(bs, offset, i << s->cluster_bits, 1,
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+                              QCOW2_DISCARD_NEVER);
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+    } while (ret == -EAGAIN);
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-    ret = update_refcount(bs, offset, i << s->cluster_bits, 1,
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-                          QCOW2_DISCARD_NEVER);
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     if (ret < 0) {
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         return ret;
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     }
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-    s->free_cluster_index = old_free_cluster_index;
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-
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     return i;
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 }
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diff --git a/block/qcow2.c b/block/qcow2.c
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index a8ad9e1..87f2958 100644
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--- a/block/qcow2.c
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+++ b/block/qcow2.c
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@@ -1580,7 +1580,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
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      */
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     BlockDriverState* bs;
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     QCowHeader *header;
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-    uint8_t* refcount_table;
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+    uint64_t* refcount_table;
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     Error *local_err = NULL;
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     int ret;
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@@ -1630,8 +1630,9 @@ static int qcow2_create2(const char *filename, int64_t total_size,
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         goto out;
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     }
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-    /* Write an empty refcount table */
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+    /* Write a refcount table with one refcount block */
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     refcount_table = g_malloc0(cluster_size);
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+    refcount_table[0] = cpu_to_be64(2 * cluster_size);
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     ret = bdrv_pwrite(bs, cluster_size, refcount_table, cluster_size);
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     g_free(refcount_table);
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@@ -1656,7 +1657,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
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         goto out;
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     }
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-    ret = qcow2_alloc_clusters(bs, 2 * cluster_size);
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+    ret = qcow2_alloc_clusters(bs, 3 * cluster_size);
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     if (ret < 0) {
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         error_setg_errno(errp, -ret, "Could not allocate clusters for qcow2 "
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                          "header and refcount table");
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diff --git a/tests/qemu-iotests/044.out b/tests/qemu-iotests/044.out
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index 5c5aa92..4789a53 100644
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--- a/tests/qemu-iotests/044.out
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+++ b/tests/qemu-iotests/044.out
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@@ -1,6 +1,6 @@
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 No errors were found on the image.
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 7292415/33554432 = 21.73% allocated, 0.00% fragmented, 0.00% compressed clusters
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-Image end offset: 4296448000
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+Image end offset: 4296152064
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 .
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 ----------------------------------------------------------------------
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 Ran 1 tests
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diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
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index f3091a9..56f8903 100755
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--- a/tests/qemu-iotests/080
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+++ b/tests/qemu-iotests/080
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@@ -56,6 +56,8 @@ offset_header_size=100
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 offset_ext_magic=$header_size
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 offset_ext_size=$((header_size + 4))
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+offset_l2_table_0=$((0x40000))
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+
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 echo
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 echo "== Huge header size =="
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 _make_test_img 64M
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@@ -143,6 +145,15 @@ poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x1
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 poke_file "$TEST_IMG" "$offset_backing_file_size" "\xff\xff\xff\xff"
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 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
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+echo
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+echo "== Invalid L2 entry (huge physical offset) =="
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+_make_test_img 64M
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+{ $QEMU_IO -c "write 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
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+poke_file "$TEST_IMG" "$offset_l2_table_0" "\xbf\xff\xff\xff\xff\xff\x00\x00"
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+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
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+poke_file "$TEST_IMG" "$offset_l2_table_0" "\x80\x00\x00\xff\xff\xff\x00\x00"
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+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
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+
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 # success, all done
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 echo "*** done"
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 rm -f $seq.full
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diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
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index 8103211..303d6c3 100644
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--- a/tests/qemu-iotests/080.out
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+++ b/tests/qemu-iotests/080.out
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@@ -63,4 +63,11 @@ no file open, try 'help open'
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 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
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 qemu-io: can't open device TEST_DIR/t.qcow2: Backing file name too long
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 no file open, try 'help open'
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+
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+== Invalid L2 entry (huge physical offset) ==
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+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
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+wrote 512/512 bytes at offset 0
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+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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+qemu-img: Could not create snapshot 'test': -27 (File too large)
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+qemu-img: Could not create snapshot 'test': -11 (Resource temporarily unavailable)
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 *** done
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-- 
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1.7.1
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