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Add -f FMT / --format FMT arg to qemu-nbd

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Currently the qemu-nbd program will auto-detect the format of
any disk it is given. This behaviour is known to be insecure.
For example, if qemu-nbd initially exposes a 'raw' file to an
unprivileged app, and that app runs

   'qemu-img create -f qcow2 -o backing_file=/etc/shadow /dev/nbd0'

then the next time the app is started, the qemu-nbd will now
detect it as a 'qcow2' file and expose /etc/shadow to the
unprivileged app.

The only way to avoid this is to explicitly tell qemu-nbd what
disk format to use on the command line, completely disabling
auto-detection. This patch adds a '-f' / '--format' arg for
this purpose, mirroring what is already available via qemu-img
and qemu commands.

  qemu-nbd --format raw -p 9000 evil.img

will now always use raw, regardless of what format 'evil.img'
looks like it contains

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
[Use errx, not err. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Daniel P. Berrange 2013-03-19 11:20:20 +00:00 committed by Anthony Liguori
parent 0ca5aa4f4c
commit e6b636779b
2 changed files with 20 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
qemu-nbd.c
View File

@ -306,6 +306,7 @@ static void nbd_accept(void *opaque)
int main(int argc, char **argv)
{
BlockDriverState *bs;
BlockDriver *drv;
off_t dev_offset = 0;
uint32_t nbdflags = 0;
bool disconnect = false;
@ -313,7 +314,7 @@ int main(int argc, char **argv)
char *device = NULL;
int port = NBD_DEFAULT_PORT;
off_t fd_size;
const char *sopt = "hVb:o:p:rsnP:c:dvk:e:t";
const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:t";
struct option lopt[] = {
{ "help", 0, NULL, 'h' },
{ "version", 0, NULL, 'V' },
@ -333,6 +334,7 @@ int main(int argc, char **argv)
#endif
{ "discard", 1, NULL, QEMU_NBD_OPT_DISCARD },
{ "shared", 1, NULL, 'e' },
{ "format", 1, NULL, 'f' },
{ "persistent", 0, NULL, 't' },
{ "verbose", 0, NULL, 'v' },
{ NULL, 0, NULL, 0 }
@ -351,6 +353,7 @@ int main(int argc, char **argv)
bool seen_aio = false;
#endif
pthread_t client_thread;
const char *fmt = NULL;
/* The client thread uses SIGTERM to interrupt the server. A signal
* handler ensures that "qemu-nbd -v -c" exits with a nice status code.
@ -454,6 +457,9 @@ int main(int argc, char **argv)
errx(EXIT_FAILURE, "Shared device number must be greater than 0\n");
}
break;
case 'f':
fmt = optarg;
break;
case 't':
persistent = 1;
break;
@ -555,9 +561,19 @@ int main(int argc, char **argv)
bdrv_init();
atexit(bdrv_close_all);
if (fmt) {
drv = bdrv_find_format(fmt);
if (!drv) {
errx(EXIT_FAILURE, "Unknown file format '%s'", fmt);
}
} else {
drv = NULL;
}
bs = bdrv_new("hda");
srcpath = argv[optind];
if ((ret = bdrv_open(bs, srcpath, NULL, flags, NULL)) < 0) {
ret = bdrv_open(bs, srcpath, NULL, flags, drv);
if (ret < 0) {
errno = -ret;
err(EXIT_FAILURE, "Failed to bdrv_open '%s'", argv[optind]);
}

2
qemu-nbd.texi
View File

@ -45,6 +45,8 @@ Export QEMU disk image using NBD protocol.
disconnect the specified device
@item -e, --shared=@var{num}
device can be shared by @var{num} clients (default @samp{1})
@item -f, --format=@var{fmt}
force block driver for format @var{fmt} instead of auto-detecting
@item -t, --persistent
don't exit on the last connection
@item -v, --verbose