qcow2: Validate snapshot table offset/size (CVE-2014-0144)

This avoid unbounded memory allocation and fixes a potential buffer
overflow on 32 bit hosts.

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

block/qcow2-snapshot.c

@@ -26,31 +26,6 @@
 #include "block/block_int.h"
 #include "block/qcow2.h"
 
-typedef struct QEMU_PACKED QCowSnapshotHeader {
-    /* header is 8 byte aligned */
-    uint64_t l1_table_offset;
-
-    uint32_t l1_size;
-    uint16_t id_str_size;
-    uint16_t name_size;
-
-    uint32_t date_sec;
-    uint32_t date_nsec;
-
-    uint64_t vm_clock_nsec;
-
-    uint32_t vm_state_size;
-    uint32_t extra_data_size; /* for extension */
-    /* extra data follows */
-    /* id_str follows */
-    /* name follows  */
-} QCowSnapshotHeader;
-
-typedef struct QEMU_PACKED QCowSnapshotExtraData {
-    uint64_t vm_state_size_large;
-    uint64_t disk_size;
-} QCowSnapshotExtraData;
-
 void qcow2_free_snapshots(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
@@ -357,6 +332,10 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     uint64_t *l1_table = NULL;
     int64_t l1_table_offset;
 
+    if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
+        return -EFBIG;
+    }
+
     memset(sn, 0, sizeof(*sn));
 
     /* Generate an ID if it wasn't passed */

block/qcow2.c

@@ -623,6 +623,21 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    /* Snapshot table offset/length */
+    if (header.nb_snapshots > QCOW_MAX_SNAPSHOTS) {
+        error_setg(errp, "Too many snapshots");
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    ret = validate_table_offset(bs, header.snapshots_offset,
+                                header.nb_snapshots,
+                                sizeof(QCowSnapshotHeader));
+    if (ret < 0) {
+        error_setg(errp, "Invalid snapshot table offset");
+        goto fail;
+    }
+
     s->snapshots_offset = header.snapshots_offset;
     s->nb_snapshots = header.nb_snapshots;
 

block/qcow2.h

@@ -38,6 +38,7 @@
 #define QCOW_CRYPT_AES  1
 
 #define QCOW_MAX_CRYPT_CLUSTERS 32
+#define QCOW_MAX_SNAPSHOTS 65536
 
 /* indicate that the refcount of the referenced cluster is exactly one. */
 #define QCOW_OFLAG_COPIED     (1ULL << 63)
@@ -97,6 +98,32 @@ typedef struct QCowHeader {
     uint32_t header_length;
 } QEMU_PACKED QCowHeader;
 
+typedef struct QEMU_PACKED QCowSnapshotHeader {
+    /* header is 8 byte aligned */
+    uint64_t l1_table_offset;
+
+    uint32_t l1_size;
+    uint16_t id_str_size;
+    uint16_t name_size;
+
+    uint32_t date_sec;
+    uint32_t date_nsec;
+
+    uint64_t vm_clock_nsec;
+
+    uint32_t vm_state_size;
+    uint32_t extra_data_size; /* for extension */
+    /* extra data follows */
+    /* id_str follows */
+    /* name follows  */
+} QCowSnapshotHeader;
+
+typedef struct QEMU_PACKED QCowSnapshotExtraData {
+    uint64_t vm_state_size_large;
+    uint64_t disk_size;
+} QCowSnapshotExtraData;
+
+
 typedef struct QCowSnapshot {
     uint64_t l1_table_offset;
     uint32_t l1_size;
@@ -202,7 +229,7 @@ typedef struct BDRVQcowState {
     AES_KEY aes_decrypt_key;
     uint64_t snapshots_offset;
     int snapshots_size;
-    int nb_snapshots;
+    unsigned int nb_snapshots;
     QCowSnapshot *snapshots;
 
     int flags;

tests/qemu-iotests/080

@@ -47,6 +47,8 @@ header_size=104
 offset_backing_file_offset=8
 offset_refcount_table_offset=48
 offset_refcount_table_clusters=56
+offset_nb_snapshots=60
+offset_snapshots_offset=64
 offset_header_size=100
 offset_ext_magic=$header_size
 offset_ext_size=$((header_size + 4))
@@ -90,6 +92,31 @@ poke_file "$TEST_IMG" "$offset_refcount_table_offset" "\xff\xff\xff\xff\xff\xff\
 poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\x00\x00\x00\x7f"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Invalid snapshot table =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_nb_snapshots" "\xff\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$TEST_IMG" "$offset_nb_snapshots" "\x7f\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+poke_file "$TEST_IMG" "$offset_snapshots_offset" "\xff\xff\xff\xff\xff\xff\x00\x00"
+poke_file "$TEST_IMG" "$offset_nb_snapshots" "\x00\x00\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+poke_file "$TEST_IMG" "$offset_snapshots_offset" "\x12\x34\x56\x78\x90\xab\xcd\xef"
+poke_file "$TEST_IMG" "$offset_nb_snapshots" "\x00\x00\x00\x00"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== Hitting snapshot table size limit =="
+_make_test_img 64M
+# Put the refcount table in a more or less safe place (16 MB)
+poke_file "$TEST_IMG" "$offset_snapshots_offset" "\x00\x00\x00\x00\x01\x00\x00\x00"
+poke_file "$TEST_IMG" "$offset_nb_snapshots" "\x00\x01\x00\x00"
+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_testdir
+{ $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/080.out

@@ -30,4 +30,21 @@ 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: Invalid reference count table offset
 no file open, try 'help open'
+
+== Invalid snapshot table ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow2: Too many snapshots
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: Too many snapshots
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: Invalid snapshot table offset
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: Invalid snapshot table offset
+no file open, try 'help open'
+
+== Hitting snapshot table size limit ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-img: Could not create snapshot 'test': -27 (File too large)
+read 512/512 bytes at offset 0
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 *** done