[PATCH 6.4 089/129] NFS: Fix a use after free in nfs_direct_join_group()

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6.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

commit be2fd1560eb57b7298aa3c258ddcca0d53ecdea3 upstream.

Be more careful when tearing down the subrequests of an O_DIRECT write
as part of a retransmission.

Reported-by: Chris Mason <clm@xxxxxx>
Fixes: ed5d588fe47f ("NFS: Try to join page groups before an O_DIRECT retransmission")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/nfs/direct.c |   26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -472,20 +472,26 @@ out:
 	return result;
 }
 
-static void
-nfs_direct_join_group(struct list_head *list, struct inode *inode)
+static void nfs_direct_join_group(struct list_head *list, struct inode *inode)
 {
-	struct nfs_page *req, *next;
+	struct nfs_page *req, *subreq;
 
 	list_for_each_entry(req, list, wb_list) {
-		if (req->wb_head != req || req->wb_this_page == req)
+		if (req->wb_head != req)
 			continue;
-		for (next = req->wb_this_page;
-				next != req->wb_head;
-				next = next->wb_this_page) {
-			nfs_list_remove_request(next);
-			nfs_release_request(next);
-		}
+		subreq = req->wb_this_page;
+		if (subreq == req)
+			continue;
+		do {
+			/*
+			 * Remove subrequests from this list before freeing
+			 * them in the call to nfs_join_page_group().
+			 */
+			if (!list_empty(&subreq->wb_list)) {
+				nfs_list_remove_request(subreq);
+				nfs_release_request(subreq);
+			}
+		} while ((subreq = subreq->wb_this_page) != req);
 		nfs_join_page_group(req, inode);
 	}
 }





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