[PATCH] Add additional error check to mm/mincore.c

[Bruce Dubbs]

I some circumstances, mincore can succeed when it shouldn't.

Example:
  Two files are mmapped to a process and they are adjacent in memory.
If mincore is run with a requested length that is too large, the
function does not differentiate between the different file pointers
within the different vma structures and inappropriately returns success.

The attached patch, against 2.6.20.3, fixes this behavior.

This behavior was found when running the Linux Test Project's mincore01
on an IA32 system.  Test 3 "unexpectedly" succeeds.

  -- Bruce
--- mm/mincore.c.old	2007-03-24 19:55:01.000000000 -0500
+++ mm/mincore.c	2007-03-24 20:13:43.000000000 -0500
@@ -43,7 +43,8 @@
  * all the arguments, we hold the mmap semaphore: we should
  * just return the amount of info we're asked for.
  */
-static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
+static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages,
+        struct file** file_struct)
 {
 	unsigned long i, nr, pgoff;
 	struct vm_area_struct *vma = find_vma(current->mm, addr);
@@ -64,7 +65,19 @@
 	 * this is what we've traditionally done, so we'll just
 	 * continue doing it.
 	 */
-	if (!vma->vm_file)
+
+    /* 
+     * Initialize file pointer to the value in the first vma structure
+     */
+
+    if ( *file_struct == NULL && vma->vm_file )
+        *file_struct = vma->vm_file;
+
+    /*
+     * Return an error if the is no file mapped of the file is different
+     */
+ 
+	if (!vma->vm_file || vma->vm_file != *file_struct)
 		return -ENOMEM;
 
 	/*
@@ -115,6 +128,7 @@
 	long retval;
 	unsigned long pages;
 	unsigned char *tmp;
+    static struct file* file = NULL;
 
 	/* Check the start address: needs to be page-aligned.. */
  	if (start & ~PAGE_CACHE_MASK)
@@ -142,7 +156,7 @@
 		 * the temporary buffer size.
 		 */
 		down_read(&current->mm->mmap_sem);
-		retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
+		retval = do_mincore(start, tmp, min(pages, PAGE_SIZE), &file);
 		up_read(&current->mm->mmap_sem);
 
 		if (retval <= 0)