Re: More info for DSM w/r/t sunffb on 2.6.15-rc6

[David S. Miller]

From: Linus Torvalds <torvalds@xxxxxxxx>
Date: Sat, 24 Dec 2005 00:32:26 -0800 (PST)

> On Fri, 23 Dec 2005, David S. Miller wrote:
> > +	if (!(vma->vm_flags & VM_SHARED))
> > +		return -EINVAL;
> > +
> 
> Side note - as I explained to Nick the other week, VM_SHARED really means 
> "shared _writable_" mapping, so you're now disallowing a shared read-only 
> open too.
> 
> Which may be fine, of course. Especially if sbusfb always ends up giving a 
> writable pfn-mapping. But I wanted to check that that was what you meant 
> to do.
> 
> To test for MAP_SHARED, either do the is_cow_mapping() thing, or check 
> the VM_MAYSHARE bit.

I did mean to test for MAP_SHARED, thanks for the test.
I've made the check like this:

diff --git a/drivers/video/sbuslib.c b/drivers/video/sbuslib.c
index 646c43f..3a74a63 100644
--- a/drivers/video/sbuslib.c
+++ b/drivers/video/sbuslib.c
@@ -46,6 +46,9 @@ int sbusfb_mmap_helper(struct sbus_mmap_
 	unsigned long off;
 	int i;
                                         
+	if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
+		return -EINVAL;
+
 	size = vma->vm_end - vma->vm_start;
 	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
 		return -EINVAL;
-
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