block/cloop: validate block_size header field (CVE-2014-0144)

Avoid unbounded s->uncompressed_block memory allocation by checking that
the block_size header field has a reasonable value.  Also enforce the
assumption that the value is a non-zero multiple of 512.

These constraints conform to cloop 2.639's code so we accept existing
image files.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/cloop.c

@@ -26,6 +26,9 @@
 #include "qemu/module.h"
 #include <zlib.h>
 
+/* Maximum compressed block size */
+#define MAX_BLOCK_SIZE (64 * 1024 * 1024)
+
 typedef struct BDRVCloopState {
     CoMutex lock;
     uint32_t block_size;
@@ -68,6 +71,26 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
         return ret;
     }
     s->block_size = be32_to_cpu(s->block_size);
+    if (s->block_size % 512) {
+        error_setg(errp, "block_size %u must be a multiple of 512",
+                   s->block_size);
+        return -EINVAL;
+    }
+    if (s->block_size == 0) {
+        error_setg(errp, "block_size cannot be zero");
+        return -EINVAL;
+    }
+
+    /* cloop's create_compressed_fs.c warns about block sizes beyond 256 KB but
+     * we can accept more.  Prevent ridiculous values like 4 GB - 1 since we
+     * need a buffer this big.
+     */
+    if (s->block_size > MAX_BLOCK_SIZE) {
+        error_setg(errp, "block_size %u must be %u MB or less",
+                   s->block_size,
+                   MAX_BLOCK_SIZE / (1024 * 1024));
+        return -EINVAL;
+    }
 
     ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);
     if (ret < 0) {

tests/qemu-iotests/075

@@ -42,11 +42,31 @@ _supported_fmt cloop
 _supported_proto generic
 _supported_os Linux
 
+block_size_offset=128
+
 echo
 echo "== check that the first sector can be read =="
 _use_sample_img simple-pattern.cloop.bz2
 $QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== block_size must be a multiple of 512 =="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$block_size_offset" "\x00\x00\x02\x01"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== block_size cannot be zero =="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$block_size_offset" "\x00\x00\x00\x00"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== huge block_size ==="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$block_size_offset" "\xff\xff\xfe\x00"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/075.out

@@ -3,4 +3,16 @@ QA output created by 075
 == check that the first sector can be read ==
 read 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== block_size must be a multiple of 512 ==
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: block_size 513 must be a multiple of 512
+no file open, try 'help open'
+
+== block_size cannot be zero ==
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: block_size cannot be zero
+no file open, try 'help open'
+
+== huge block_size ===
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: block_size 4294966784 must be 64 MB or less
+no file open, try 'help open'
 *** done