[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>

1 files changed, 25 insertions, 5 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 2af50831183f..2e140a6ae22e 100644
--- 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);