From 951cf3bc525e30c290318f50b14ef83b9dff13b7 Mon Sep 17 00:00:00 2001
From: Chuck Lever <chuck.lever@oracle.com>
Date: Tue, 11 Mar 2025 08:51:19 +0900
Subject: [PATCH] NFSD: Prevent NULL dereference in nfsd4_process_cb_update()

BugLink: https://bugs.launchpad.net/bugs/2101915

[ Upstream commit 1e02c641c3a43c88cecc08402000418e15578d38 ]

@ses is initialized to NULL. If __nfsd4_find_backchannel() finds no
available backchannel session, setup_callback_client() will try to
dereference @ses and segfault.

Fixes: dcbeaa68dbbd ("nfsd4: allow backchannel recovery")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
CVE-2024-53217
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
 fs/nfsd/nfs4callback.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 30aa241038eb..c8d654c50f6e 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -1450,6 +1450,8 @@ static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
 		ses = c->cn_session;
 	}
 	spin_unlock(&clp->cl_lock);
+	if (!c)
+		return;
 
 	err = setup_callback_client(clp, &conn, ses);
 	if (err) {