fs: afs: Fix a possible null-pointer dereference in afs_put_read()

In afs_read_dir(), there is an if statement on line 255 to check whether
req->pages is NULL:
	if (!req->pages)
		goto error;

If req->pages is NULL, afs_put_read() on line 337 is executed.
In afs_put_read(), req->pages[i] is used on line 195.
Thus, a possible null-pointer dereference may occur in this case.

To fix this possible bug, an if statement is added in afs_put_read() to
check req->pages.

This bug is found by a static analysis tool STCheck written by us.

Fixes: f3ddee8dc4e2 ("afs: Fix directory handling")
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 56b6957..dd3c55c 100644 (file)
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -191,11 +191,13 @@ void afs_put_read(struct afs_read *req)
        int i;
 
        if (refcount_dec_and_test(&req->usage)) {
-               for (i = 0; i < req->nr_pages; i++)
-                       if (req->pages[i])
-                               put_page(req->pages[i]);
-               if (req->pages != req->array)
-                       kfree(req->pages);
+               if (req->pages) {
+                       for (i = 0; i < req->nr_pages; i++)
+                               if (req->pages[i])
+                                       put_page(req->pages[i]);
+                       if (req->pages != req->array)
+                               kfree(req->pages);
+               }
                kfree(req);
        }
 }