[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 2af50831183fe6cab2769c3ee9119720c8a64d5c..2e140a6ae22e2f20522df9291f290d89c3c13250 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -122,19 +122,35 @@ unsigned int kobjsize(const void *objp)
 }
 
 /*
- * 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 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                        vmas[i] = vma;
                start += PAGE_SIZE;
        }
-       return(i);
+
+       return i;
+
+finish_or_fault:
+       return i ? : -EFAULT;
 }
 
 EXPORT_SYMBOL(get_user_pages);