block: Fix error path segfault in bdrv_open()

Using an invalid option for a block device that is opened with
BDRV_O_PROTOCOL led to drv = NULL, and when trying to include the driver
name in the error message, qemu dereferenced it:

    $ x86_64-softmmu/qemu-system-x86_64 -drive file=/tmp/test.qcow2,file.foo=bar
    Segmentation fault (core dumped)

With this patch applied, the expected error message is printed:

    $ x86_64-softmmu/qemu-system-x86_64 -drive file=/tmp/test.qcow2,file.foo=bar
    qemu-system-x86_64: -drive file=/tmp/test.qcow2,file.foo=bar: could
    not open disk image /tmp/test.qcow2: Block protocol 'file' doesn't
    support the option 'foo'
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NBenoit Canet <benoit@irqsave.net>

block.c

@@ -1234,6 +1234,7 @@ int bdrv_open(BlockDriverState **pbs, const char *filename,
         ret = bdrv_file_open(bs, filename, &options, flags & ~BDRV_O_PROTOCOL,
                              &local_err);
         if (!ret) {
+            drv = bs->drv;
             goto done;
         } else if (bs->drv) {
             goto close_and_fail;

tests/qemu-iotests/051

@@ -77,6 +77,15 @@ run_qemu -drive file="$TEST_IMG",format=qcow2,unknown_opt=on
 run_qemu -drive file="$TEST_IMG",format=qcow2,unknown_opt=1234
 run_qemu -drive file="$TEST_IMG",format=qcow2,unknown_opt=foo
 
+echo
+echo === Unknown protocol option ===
+echo
+
+run_qemu -drive file="$TEST_IMG",format=qcow2,file.unknown_opt=
+run_qemu -drive file="$TEST_IMG",format=qcow2,file.unknown_opt=on
+run_qemu -drive file="$TEST_IMG",format=qcow2,file.unknown_opt=1234
+run_qemu -drive file="$TEST_IMG",format=qcow2,file.unknown_opt=foo
+
 echo
 echo === Invalid format ===
 echo

tests/qemu-iotests/051.out

@@ -17,6 +17,21 @@ Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,unknown_opt=foo
 QEMU_PROG: -drive file=TEST_DIR/t.qcow2,format=qcow2,unknown_opt=foo: could not open disk image TEST_DIR/t.qcow2: Block format 'qcow2' used by device 'ide0-hd0' doesn't support the option 'unknown_opt'
 
 
+=== Unknown protocol option ===
+
+Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=: could not open disk image TEST_DIR/t.qcow2: Block protocol 'file' doesn't support the option 'unknown_opt'
+
+Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=on
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=on: could not open disk image TEST_DIR/t.qcow2: Block protocol 'file' doesn't support the option 'unknown_opt'
+
+Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=1234
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=1234: could not open disk image TEST_DIR/t.qcow2: Block protocol 'file' doesn't support the option 'unknown_opt'
+
+Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=foo
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,format=qcow2,file.unknown_opt=foo: could not open disk image TEST_DIR/t.qcow2: Block protocol 'file' doesn't support the option 'unknown_opt'
+
+
 === Invalid format ===
 
 Testing: -drive file=TEST_DIR/t.qcow2,format=foo