| Message ID | 20210510043045.15238-1-lizhijian@cn.fujitsu.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Improve backing file validation | expand |
On Mon, May 10, 2021 at 12:30:45PM +0800, Li Zhijian wrote: > Image below user cases: > case 1: > ``` > $ qemu-img create -f raw source.raw 1G > $ qemu-img create -f qcow2 -F raw -b source.raw ./source.raw > qemu-img info source.raw > image: source.raw > file format: qcow2 > virtual size: 193K (197120 bytes) > disk size: 196K > cluster_size: 65536 > backing file: source.raw <<<<<< > backing file format: raw > Format specific information: > compat: 1.1 > lazy refcounts: false > refcount bits: 16 > corrupt: false > ``` > > case 2: > ``` > $ qemu-img create -f raw source.raw 1G > $ ln -sf source.raw destination.qcow2 > $ qemu-img create -f qcow2 -F raw -b source.raw ./destination.qcow2 > qemu-img info source.raw > image: source.raw > file format: qcow2 <<<<<< > virtual size: 2.0G (2147483648 bytes) > disk size: 196K > cluster_size: 65536 > backing file: source.raw > backing file format: raw > Format specific information: > compat: 1.1 > lazy refcounts: false > refcount bits: 16 > corrupt: false > ``` > Generally, we don't expect to corrupte the source.raw anyway, while > actually it does. > > Here we validate the realpath of file instead the input string. That still won't handle the case where you use hard links $ ln source.raw destination.qcow2 To properly validate the scenarios I think it is neccessary to ignore the filename sentirely. Instead attempt to open both files, and if successful, fstat() them both, and then compare the st_dev + st_ino fields. > Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com> > --- > block.c | 46 +++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 39 insertions(+), 7 deletions(-) > > diff --git a/block.c b/block.c > index 9ad725d205..523845b763 100644 > --- a/block.c > +++ b/block.c > @@ -6431,6 +6431,44 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs) > return true; > } > > +static bool validate_backing_file(const char *filename, > + const char *backing_file, Error **errp) > +{ > + bool ret = false; > + char *rf, *real_filename = g_malloc0(PATH_MAX + 1); > + char *rb, *real_backing = g_malloc0(PATH_MAX + 1); Don't do this - PATH_MAX is not required to be defined by POSIX, and when it is defined, POSIX states that it may be so large that it is inappropriate to use for allocation. > + > + rf = realpath(filename, real_filename); GLibC, macOS, FreeBSD, NetBSD and OpenBSD all implement the POSIX.1-2008 extension that allows the output buffer to be NULL, in which case realpath returns a newly allocated string of the correct size. Windows doesn't provide realpath at all, so I'm surprised this doesn't break the windows builds. > + if (!rf) { > + if (errno == ENOENT) { > + /* filename doesn't exit, ignore it */ > + rf = (char *)filename; > + } else { > + error_setg(errp, "Failed to resolve %s", filename); > + goto out; > + } > + } > + rb = realpath(backing_file, real_backing); > + if (!rb) { > + error_setg(errp, "Failed to resolve %s", backing_file); > + goto out; > + } > + if (!strcmp(rf, rb)) { > + error_setg(errp, "Error: Trying to create an image with the " > + "same filename as the backing file"); > + goto out; > + } > + if (backing_file[0] == '\0') { > + error_setg(errp, "Expected backing file name, got empty string"); > + goto out; > + } > + ret = true; > +out: > + g_free(real_filename); > + g_free(real_backing); > + return ret; > +} > + > void bdrv_img_create(const char *filename, const char *fmt, > const char *base_filename, const char *base_fmt, > char *options, uint64_t img_size, int flags, bool quiet, > @@ -6507,13 +6545,7 @@ void bdrv_img_create(const char *filename, const char *fmt, > > backing_file = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE); > if (backing_file) { > - if (!strcmp(filename, backing_file)) { > - error_setg(errp, "Error: Trying to create an image with the " > - "same filename as the backing file"); > - goto out; > - } > - if (backing_file[0] == '\0') { > - error_setg(errp, "Expected backing file name, got empty string"); > + if (!validate_backing_file(filename, backing_file, errp)) { > goto out; > } > } > -- > 2.30.2 > > > > Regards, Daniel
On 2021/5/10 16:41, Daniel P. Berrangé wrote: > On Mon, May 10, 2021 at 12:30:45PM +0800, Li Zhijian wrote: >> Image below user cases: >> case 1: >> ``` >> $ qemu-img create -f raw source.raw 1G >> $ qemu-img create -f qcow2 -F raw -b source.raw ./source.raw >> qemu-img info source.raw >> image: source.raw >> file format: qcow2 >> virtual size: 193K (197120 bytes) >> disk size: 196K >> cluster_size: 65536 >> backing file: source.raw <<<<<< >> backing file format: raw >> Format specific information: >> compat: 1.1 >> lazy refcounts: false >> refcount bits: 16 >> corrupt: false >> ``` >> >> case 2: >> ``` >> $ qemu-img create -f raw source.raw 1G >> $ ln -sf source.raw destination.qcow2 >> $ qemu-img create -f qcow2 -F raw -b source.raw ./destination.qcow2 >> qemu-img info source.raw >> image: source.raw >> file format: qcow2 <<<<<< >> virtual size: 2.0G (2147483648 bytes) >> disk size: 196K >> cluster_size: 65536 >> backing file: source.raw >> backing file format: raw >> Format specific information: >> compat: 1.1 >> lazy refcounts: false >> refcount bits: 16 >> corrupt: false >> ``` >> Generally, we don't expect to corrupte the source.raw anyway, while >> actually it does. >> >> Here we validate the realpath of file instead the input string. > That still won't handle the case where you use hard links > > $ ln source.raw destination.qcow2 > > To properly validate the scenarios I think it is neccessary > to ignore the filename sentirely. > > Instead attempt to open both files, and if successful, fstat() > them both, and then compare the st_dev + st_ino fields. Sounds great, i will update it. Thanks Zhijian
diff --git a/block.c b/block.c index 9ad725d205..523845b763 100644 --- a/block.c +++ b/block.c @@ -6431,6 +6431,44 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs) return true; } +static bool validate_backing_file(const char *filename, + const char *backing_file, Error **errp) +{ + bool ret = false; + char *rf, *real_filename = g_malloc0(PATH_MAX + 1); + char *rb, *real_backing = g_malloc0(PATH_MAX + 1); + + rf = realpath(filename, real_filename); + if (!rf) { + if (errno == ENOENT) { + /* filename doesn't exit, ignore it */ + rf = (char *)filename; + } else { + error_setg(errp, "Failed to resolve %s", filename); + goto out; + } + } + rb = realpath(backing_file, real_backing); + if (!rb) { + error_setg(errp, "Failed to resolve %s", backing_file); + goto out; + } + if (!strcmp(rf, rb)) { + error_setg(errp, "Error: Trying to create an image with the " + "same filename as the backing file"); + goto out; + } + if (backing_file[0] == '\0') { + error_setg(errp, "Expected backing file name, got empty string"); + goto out; + } + ret = true; +out: + g_free(real_filename); + g_free(real_backing); + return ret; +} + void bdrv_img_create(const char *filename, const char *fmt, const char *base_filename, const char *base_fmt, char *options, uint64_t img_size, int flags, bool quiet, @@ -6507,13 +6545,7 @@ void bdrv_img_create(const char *filename, const char *fmt, backing_file = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE); if (backing_file) { - if (!strcmp(filename, backing_file)) { - error_setg(errp, "Error: Trying to create an image with the " - "same filename as the backing file"); - goto out; - } - if (backing_file[0] == '\0') { - error_setg(errp, "Expected backing file name, got empty string"); + if (!validate_backing_file(filename, backing_file, errp)) { goto out; } }
Image below user cases: case 1: ``` $ qemu-img create -f raw source.raw 1G $ qemu-img create -f qcow2 -F raw -b source.raw ./source.raw qemu-img info source.raw image: source.raw file format: qcow2 virtual size: 193K (197120 bytes) disk size: 196K cluster_size: 65536 backing file: source.raw <<<<<< backing file format: raw Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false ``` case 2: ``` $ qemu-img create -f raw source.raw 1G $ ln -sf source.raw destination.qcow2 $ qemu-img create -f qcow2 -F raw -b source.raw ./destination.qcow2 qemu-img info source.raw image: source.raw file format: qcow2 <<<<<< virtual size: 2.0G (2147483648 bytes) disk size: 196K cluster_size: 65536 backing file: source.raw backing file format: raw Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false ``` Generally, we don't expect to corrupte the source.raw anyway, while actually it does. Here we validate the realpath of file instead the input string. Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com> --- block.c | 46 +++++++++++++++++++++++++++++++++++++++------- 1 file changed, 39 insertions(+), 7 deletions(-)