From a2b10eec76a72aa7fe63e797181b93f69de9600e Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Tue, 25 Mar 2014 14:23:34 +0100

Subject: [PATCH 27/49] qcow2: Don't rely on free_cluster_index in alloc_refcount_block() (CVE-2014-0147)

RH-Author: Kevin Wolf <kwolf@redhat.com>

Message-id: <1395753835-7591-28-git-send-email-kwolf@redhat.com>

Patchwork-id: n/a

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)

Bugzilla: 1079339

RH-Acked-by: Jeff Cody <jcody@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1079339

Upstream status: Embargoed

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)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

---

 block/qcow2-refcount.c     |   74 ++++++++++++++++++++++---------------------

 block/qcow2.c              |    7 ++--

 tests/qemu-iotests/044.out |    2 +-

 tests/qemu-iotests/080     |   11 ++++++

 tests/qemu-iotests/080.out |    7 ++++

 5 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c

index 13ea5f7..54bcbd1 100644

--- a/block/qcow2-refcount.c

+++ b/block/qcow2-refcount.c

@@ -193,10 +193,11 @@ 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

@@ -281,7 +282,10 @@ 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);

@@ -304,8 +308,7 @@ 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);

@@ -338,8 +341,6 @@ 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));

@@ -402,18 +403,19 @@ 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);

@@ -659,12 +661,15 @@ 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;

     }

@@ -677,7 +682,6 @@ 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;

@@ -686,30 +690,28 @@ 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;

 }

diff --git a/block/qcow2.c b/block/qcow2.c

index a8ad9e1..87f2958 100644

--- a/block/qcow2.c

+++ b/block/qcow2.c

@@ -1580,7 +1580,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,

      */

     BlockDriverState* bs;

     QCowHeader *header;

-    uint8_t* refcount_table;

+    uint64_t* refcount_table;

     Error *local_err = NULL;

     int ret;

@@ -1630,8 +1630,9 @@ static int qcow2_create2(const char *filename, int64_t total_size,

         goto out;

     }

-    /* Write an empty refcount table */

+    /* Write a refcount table with one refcount block */

     refcount_table = g_malloc0(cluster_size);

+    refcount_table[0] = cpu_to_be64(2 * cluster_size);

     ret = bdrv_pwrite(bs, cluster_size, refcount_table, cluster_size);

     g_free(refcount_table);

@@ -1656,7 +1657,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,

         goto out;

     }

-    ret = qcow2_alloc_clusters(bs, 2 * cluster_size);

+    ret = qcow2_alloc_clusters(bs, 3 * cluster_size);

     if (ret < 0) {

         error_setg_errno(errp, -ret, "Could not allocate clusters for qcow2 "

                          "header and refcount table");

diff --git a/tests/qemu-iotests/044.out b/tests/qemu-iotests/044.out

index 5c5aa92..4789a53 100644

--- a/tests/qemu-iotests/044.out

+++ b/tests/qemu-iotests/044.out

@@ -1,6 +1,6 @@

 No errors were found on the image.

 7292415/33554432 = 21.73% allocated, 0.00% fragmented, 0.00% compressed clusters

-Image end offset: 4296448000

+Image end offset: 4296152064

 .

 ----------------------------------------------------------------------

 Ran 1 tests

diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080

index f3091a9..56f8903 100755

--- a/tests/qemu-iotests/080

+++ b/tests/qemu-iotests/080

@@ -56,6 +56,8 @@ offset_header_size=100

 offset_ext_magic=$header_size

 offset_ext_size=$((header_size + 4))

+offset_l2_table_0=$((0x40000))

+

 echo

 echo "== Huge header size =="

 _make_test_img 64M

@@ -143,6 +145,15 @@ poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x1

 poke_file "$TEST_IMG" "$offset_backing_file_size" "\xff\xff\xff\xff"

 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir

+echo

+echo "== Invalid L2 entry (huge physical offset) =="

+_make_test_img 64M

+{ $QEMU_IO -c "write 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir

+poke_file "$TEST_IMG" "$offset_l2_table_0" "\xbf\xff\xff\xff\xff\xff\x00\x00"

+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir

+poke_file "$TEST_IMG" "$offset_l2_table_0" "\x80\x00\x00\xff\xff\xff\x00\x00"

+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir

+

 # success, all done

 echo "*** done"

 rm -f $seq.full

diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out

index 8103211..303d6c3 100644

--- a/tests/qemu-iotests/080.out

+++ b/tests/qemu-iotests/080.out

@@ -63,4 +63,11 @@ no file open, try 'help open'

 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 

 qemu-io: can't open device TEST_DIR/t.qcow2: Backing file name too long

 no file open, try 'help open'

+

+== Invalid L2 entry (huge physical offset) ==

+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 

+wrote 512/512 bytes at offset 0

+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

+qemu-img: Could not create snapshot 'test': -27 (File too large)

+qemu-img: Could not create snapshot 'test': -11 (Resource temporarily unavailable)

 *** done

-- 

1.7.1