[PATCH] NOMMU: Check VMA protections
Check the VMA protections in get_user_pages() against what's being asked.
This checks to see that we don't accidentally write on a non-writable VMA or
permit an I/O mapping VMA to be accessed (which may lack page structs).
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index 2af5083..2e140a6 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -122,19 +122,35 @@
}
/*
- * The nommu dodgy version :-)
+ * get a list of pages in an address range belonging to the specified process
+ * and indicate the VMA that covers each page
+ * - this is potentially dodgy as we may end incrementing the page count of a
+ * slab page or a secondary page from a compound page
+ * - don't permit access to VMAs that don't support it, such as I/O mappings
*/
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, int write, int force,
struct page **pages, struct vm_area_struct **vmas)
{
- int i;
struct vm_area_struct *vma;
+ unsigned long vm_flags;
+ int i;
+
+ /* calculate required read or write permissions.
+ * - if 'force' is set, we only require the "MAY" flags.
+ */
+ vm_flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
+ vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
for (i = 0; i < len; i++) {
vma = find_vma(mm, start);
- if(!vma)
- return i ? : -EFAULT;
+ if (!vma)
+ goto finish_or_fault;
+
+ /* protect what we can, including chardevs */
+ if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
+ !(vm_flags & vma->vm_flags))
+ goto finish_or_fault;
if (pages) {
pages[i] = virt_to_page(start);
@@ -145,7 +161,11 @@
vmas[i] = vma;
start += PAGE_SIZE;
}
- return(i);
+
+ return i;
+
+finish_or_fault:
+ return i ? : -EFAULT;
}
EXPORT_SYMBOL(get_user_pages);
