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Subject[127/262] um: fix ubd cow size
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Weinberger <richard@nod.at>

commit 8535639810e578960233ad39def3ac2157b0c3ec upstream.

ubd_file_size() cannot use ubd_dev->cow.file because at this time
ubd_dev->cow.file is not initialized.
Therefore, ubd_file_size() will always report a wrong disk size when
COW files are used.
Reading from /dev/ubd* would crash the kernel.

We have to read the correct disk size from the COW file's backing
file.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/um/drivers/ubd_kern.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)

--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -513,8 +513,37 @@ __uml_exitcall(kill_io_thread);
static inline int ubd_file_size(struct ubd *ubd_dev, __u64 *size_out)
{
char *file;
+ int fd;
+ int err;

- file = ubd_dev->cow.file ? ubd_dev->cow.file : ubd_dev->file;
+ __u32 version;
+ __u32 align;
+ char *backing_file;
+ time_t mtime;
+ unsigned long long size;
+ int sector_size;
+ int bitmap_offset;
+
+ if (ubd_dev->file && ubd_dev->cow.file) {
+ file = ubd_dev->cow.file;
+
+ goto out;
+ }
+
+ fd = os_open_file(ubd_dev->file, global_openflags, 0);
+ if (fd < 0)
+ return fd;
+
+ err = read_cow_header(file_reader, &fd, &version, &backing_file, \
+ &mtime, &size, &sector_size, &align, &bitmap_offset);
+ os_close_file(fd);
+
+ if(err == -EINVAL)
+ file = ubd_dev->file;
+ else
+ file = backing_file;
+
+out:
return os_file_size(file, size_out);
}




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