From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Thu, 30 Apr 2020 19:08:26 +0000 (-0400)
Subject: NFS: Fix a race in __nfs_list_for_each_server()
X-Git-Tag: v5.7-rc4~5^2
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=9c07b75b80eeff714420fb6a4c880b284e529d0f;p=users%2Fwilly%2Flinux.git

NFS: Fix a race in __nfs_list_for_each_server()

The struct nfs_server gets put on the cl_superblocks list before
the server->super field has been initialised, in which case the
call to nfs_sb_active() will Oops. Add a check to ensure that
we skip such a list entry.

Fixes: 3c9e502b59fb ("NFS: Add a helper nfs_client_for_each_server()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 59ef3b13ccca..bdb6d0c2e755 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -185,7 +185,7 @@ static int __nfs_list_for_each_server(struct list_head *head,
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(server, head, client_link) {
-		if (!nfs_sb_active(server->super))
+		if (!(server->super && nfs_sb_active(server->super)))
 			continue;
 		rcu_read_unlock();
 		if (last)