[PATCH 5.15 085/171] nfsd: Fix nsfd startup race (again)

Greg Kroah-Hartman
2021-12-13T10:21:49Z

From: Alexander Sverdlin <alexander.sverdlin@nokia.com>

commit b10252c7ae9c9d7c90552f88b544a44ee773af64 upstream.

Commit bd5ae9288d64 ("nfsd: register pernet ops last, unregister first")
has re-opened rpc_pipefs_event() race against nfsd_net_id registration
(register_pernet_subsys()) which has been fixed by commit bb7ffbf29e76
("nfsd: fix nsfd startup race triggering BUG_ON").

Restore the order of register_pernet_subsys() vs register_cld_notifier().
Add WARN_ON() to prevent a future regression.

Crash info:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000012
CPU: 8 PID: 345 Comm: mount Not tainted 5.4.144-... #1
pc : rpc_pipefs_event+0x54/0x120 [nfsd]
lr : rpc_pipefs_event+0x48/0x120 [nfsd]
Call trace:
rpc_pipefs_event+0x54/0x120 [nfsd]
blocking_notifier_call_chain
rpc_fill_super
get_tree_keyed
rpc_fs_get_tree
vfs_get_tree
do_mount
ksys_mount
__arm64_sys_mount
el0_svc_handler
el0_svc

Fixes: bd5ae9288d64 ("nfsd: register pernet ops last, unregister first")
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/nfs4recover.c | 1 +
fs/nfsd/nfsctl.c | 14 +++++++-------
2 files changed, 8 insertions(+), 7 deletions(-)

--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -2156,6 +2156,7 @@ static struct notifier_block nfsd4_cld_b
int
register_cld_notifier(void)
{
+ WARN_ON(!nfsd_net_id);
return rpc_pipefs_notifier_register(&nfsd4_cld_block);
}

--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1521,12 +1521,9 @@ static int __init init_nfsd(void)
int retval;
printk(KERN_INFO "Installing knfsd (copyright (C) 1996 okir@monad.swb.de).\n");

- retval = register_cld_notifier();
- if (retval)
- return retval;
retval = nfsd4_init_slabs();
if (retval)
- goto out_unregister_notifier;
+ return retval;
retval = nfsd4_init_pnfs();
if (retval)
goto out_free_slabs;
@@ -1545,9 +1542,14 @@ static int __init init_nfsd(void)
goto out_free_exports;
retval = register_pernet_subsys(&nfsd_net_ops);
if (retval < 0)
+ goto out_free_filesystem;
+ retval = register_cld_notifier();
+ if (retval)
goto out_free_all;
return 0;
out_free_all:
+ unregister_pernet_subsys(&nfsd_net_ops);
+out_free_filesystem:
unregister_filesystem(&nfsd_fs_type);
out_free_exports:
remove_proc_entry("fs/nfs/exports", NULL);
@@ -1561,13 +1563,12 @@ out_free_pnfs:
nfsd4_exit_pnfs();
out_free_slabs:
nfsd4_free_slabs();
-out_unregister_notifier:
- unregister_cld_notifier();
return retval;
}

static void __exit exit_nfsd(void)
{
+ unregister_cld_notifier();
unregister_pernet_subsys(&nfsd_net_ops);
nfsd_drc_slab_free();
remove_proc_entry("fs/nfs/exports", NULL);
@@ -1577,7 +1578,6 @@ static void __exit exit_nfsd(void)
nfsd4_free_slabs();
nfsd4_exit_pnfs();
unregister_filesystem(&nfsd_fs_type);
- unregister_cld_notifier();
}

MODULE_AUTHOR("Olaf Kirch <okir@monad.swb.de>");