AFS: Stop readlink() on AFS crashing due to NULL 'file' ptr

kAFS crashes when asked to read a symbolic link because page_getlink()
passes a NULL file pointer to read_mapping_page(), but afs_readpage()
expects a file pointer from which to extract a key.

Modify afs_readpage() to request the appropriate key from the calling
process's keyrings if a file struct is not supplied with one attached.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 0149dab..681c2a7 100644 (file)
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -134,9 +134,16 @@ static int afs_readpage(struct file *file, struct page *page)
 
        inode = page->mapping->host;
 
-       ASSERT(file != NULL);
-       key = file->private_data;
-       ASSERT(key != NULL);
+       if (file) {
+               key = file->private_data;
+               ASSERT(key != NULL);
+       } else {
+               key = afs_request_key(AFS_FS_S(inode->i_sb)->volume->cell);
+               if (IS_ERR(key)) {
+                       ret = PTR_ERR(key);
+                       goto error_nokey;
+               }
+       }
 
        _enter("{%x},{%lu},{%lu}", key_serial(key), inode->i_ino, page->index);
 
@@ -207,12 +214,17 @@ static int afs_readpage(struct file *file, struct page *page)
                unlock_page(page);
        }
 
+       if (!file)
+               key_put(key);
        _leave(" = 0");
        return 0;
 
 error:
        SetPageError(page);
        unlock_page(page);
+       if (!file)
+               key_put(key);
+error_nokey:
        _leave(" = %d", ret);
        return ret;
 }