Re: 2.5.55-rmk1: user space lossage

[Andrew Morton <akpm@digeo.com>]

David Woodhouse <dwmw2@infradead.org> wrote:
>
> 
> 
> -  	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
> +-  	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
> ++ 	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))

Yup.



We cannot clear VM_MAYWRITE in there - it turns writeable MAP_PRIVATE
mappings into readonly ones.

So change it back to the 2.4 form - disallow a writeable MAP_SHARED mapping
against filesystems which do no implement ->writepage().


 filemap.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c
--- 25/mm/filemap.c~generic_file_readonly_mmap-fix	2003-01-23 01:55:41.000000000 -0800
+++ 25-akpm/mm/filemap.c	2003-01-23 02:04:05.000000000 -0800
@@ -1308,11 +1308,13 @@ int generic_file_mmap(struct file * file
 	return 0;
 }
 
+/*
+ * This is for filesystems which do not implement ->writepage.
+ */
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
 		return -EINVAL;
-	vma->vm_flags &= ~VM_MAYWRITE;
 	return generic_file_mmap(file, vma);
 }
 #else

_