From e6b636779b51c97e67694be740ee972c52460c59 Mon Sep 17 00:00:00 2001 From: "Daniel P. Berrange" Date: Tue, 19 Mar 2013 11:20:20 +0000 Subject: [PATCH] Add -f FMT / --format FMT arg to qemu-nbd 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 [Use errx, not err. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Anthony Liguori --- qemu-nbd.c | 20 ++++++++++++++++++-- qemu-nbd.texi | 2 ++ 2 files changed, 20 insertions(+), 2 deletions(-) diff --git a/qemu-nbd.c b/qemu-nbd.c index ca722ed425..9c31d45706 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -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]); } diff --git a/qemu-nbd.texi b/qemu-nbd.texi index 5f3f3e3276..6055ec693b 100644 --- a/qemu-nbd.texi +++ b/qemu-nbd.texi @@ -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 -- 2.39.2