block.c | 46 +++++++++++++++++++++++++++++++++++++++------- 1 file changed, 39 insertions(+), 7 deletions(-)
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(-)
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;
}
}
--
2.30.2
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
--
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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
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