[PATCH] uclinux: fix mmap() of directory for nommu case

I was playing with blackfin when i hit a neat bug ... doing an open() on a
directory and then passing that fd to mmap() would cause the kernel to hang

after poking into the code a bit more, i found that
mm/nommu.c:validate_mmap_request() checks the length and if it is 0, just
returns the address ... this is in stark contrast to mmu's
mm/mmap.c:do_mmap_pgoff() where it returns -EINVAL for 0 length requests ...
i then noticed that some other parts of the logic is out of date between the
two funcs, so perhaps that's the easy fix ?
Signed-off-by: NGreg Ungerer <gerg@uclinux.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/nommu.c

@@ -497,15 +497,17 @@ static int validate_mmap_request(struct file *file,
 	    (flags & MAP_TYPE) != MAP_SHARED)
 		return -EINVAL;
 
-	if (PAGE_ALIGN(len) == 0)
-		return addr;
-
-	if (len > TASK_SIZE)
+	if (!len)
 		return -EINVAL;
 
+	/* Careful about overflows.. */
+	len = PAGE_ALIGN(len);
+	if (!len || len > TASK_SIZE)
+		return -ENOMEM;
+
 	/* offset overflow? */
 	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
-		return -EINVAL;
+		return -EOVERFLOW;
 
 	if (file) {
 		/* validate file mapping requests */