qcow2: Fix header extension size check

After reading the extension header, offset is incremented, but not checked against end_offset any more. This way an integer overflow could happen when checking whether the extension end is within the allowed range, effectively disabling the check. This patch adds the missing check and a test case for it. Cc: qemu-stable@nongnu.org Reported-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-id: 1416935562-7760-2-git-send-email-kwolf@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
amazonsx · Dec 10, 2014 · 2ebafc8 · 2ebafc8
1 parent 3dc7ca3
commit 2ebafc8
Show file tree

Hide file tree

Showing 3 changed files with 5 additions and 1 deletion.
diff --git a/block/qcow2.c b/block/qcow2.c
@@ -117,7 +117,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
 #ifdef DEBUG_EXT
         printf("ext.magic = 0x%x\n", ext.magic);
 #endif
-        if (ext.len > end_offset - offset) {
+        if (offset > end_offset || ext.len > end_offset - offset) {
             error_setg(errp, "Header extension too large");
             return -EINVAL;
         }

diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
@@ -78,6 +78,8 @@ poke_file "$TEST_IMG" "$offset_backing_file_offset" "\xff\xff\xff\xff\xff\xff\xf
 poke_file "$TEST_IMG" "$offset_ext_magic" "\x12\x34\x56\x78"
 poke_file "$TEST_IMG" "$offset_ext_size" "\x7f\xff\xff\xff"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x00\x$(printf %x $offset_ext_size)"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 

diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
@@ -13,6 +13,8 @@ qemu-io: can't open device TEST_DIR/t.qcow2: Invalid backing file offset
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow2: Header extension too large
 no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: Header extension too large
+no file open, try 'help open'
 
 == Huge refcount table size ==
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864