fuse: fix fuse_retrieve

Fix two bugs in fuse_retrieve():

 - retrieving more than one page would yield repeated instances of the
   first page

 - if more than FUSE_MAX_PAGES_PER_REQ pages were requested than the
   request page array would overflow

fuse_retrieve() was added in 2.6.36 and these bugs had been there since the
beginning.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@vger.kernel.org

fs/fuse/dev.c

@@ -1512,7 +1512,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	else if (outarg->offset + num > file_size)
 		num = file_size - outarg->offset;
 
-	while (num) {
+	while (num && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
 		struct page *page;
 		unsigned int this_num;
 
@@ -1526,6 +1526,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 
 		num -= this_num;
 		total_len += this_num;
+		index++;
 	}
 	req->misc.retrieve_in.offset = outarg->offset;
 	req->misc.retrieve_in.size = total_len;