[PATCH 1/3] nfsd: provide proper locking for all write_ function

[NeilBrown <neil@brown.name>]

write_foo functions are called to handle IO to files in /proc/fs/nfsd/.
They can be called at any time and so generally need locking to ensure
they don't happen at an awkward time.

Many already take nfsd_mutex and check if nfsd_serv has been set.  This
ensures they only run when the server is fully configured.

write_filehandle() does *not* need locking.  It interacts with the
export table which is set up when the netns is set up, so it is always
valid and it has its own locking.  write_filehandle() is needed before
the nfs server is started so checking nfsd_serv would be wrong.

The remaining files which do not have any locking are
write_v4_end_grace(), write_unlock_ip(), and write_unlock_fs().
None of these make sense when the nfs server is not running and there is
evidence that write_v4_end_grace() can race with ->client_tracking_op
setup/shutdown and cause problems.

This patch adds locking to these three and ensures the "unlock"
functions abort if ->nfsd_serv is not set.  It uses
    guard(mutex)(&nfsd_mutex);
so there is no need to ensure we unlock on every patch.

Reported-by: Li Lingfeng <lilingfeng3@huawei.com>
Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/nfsd/nfsctl.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 3f3e9f6c4250..0e7e89dc730b 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -221,6 +221,12 @@ static ssize_t write_unlock_ip(struct file *file, char *buf, size_t size)
 	size_t salen = sizeof(address);
 	char *fo_path;
 	struct net *net = netns(file);
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	guard(mutex)(&nfsd_mutex);
+	if (!nn->nfsd_serv)
+		/* There cannot be any files to unlock */
+		return -EINVAL;
 
 	/* sanity check */
 	if (size == 0)
@@ -259,6 +265,12 @@ static ssize_t write_unlock_fs(struct file *file, char *buf, size_t size)
 	struct path path;
 	char *fo_path;
 	int error;
+	struct nfsd_net *nn = net_generic(netns(file), nfsd_net_id);
+
+	guard(mutex)(&nfsd_mutex);
+	if (!nn->nfsd_serv)
+		/* There cannot be any files to unlock */
+		return -EINVAL;
 
 	/* sanity check */
 	if (size == 0)
@@ -1053,6 +1065,7 @@ static ssize_t write_recoverydir(struct file *file, char *buf, size_t size)
 }
 #endif
 
+
 /*
  * write_v4_end_grace - release grace period for nfsd's v4.x lock manager
  *
@@ -1077,6 +1090,7 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
 {
 	struct nfsd_net *nn = net_generic(netns(file), nfsd_net_id);
 
+	guard(mutex)(&nfsd_mutex);
 	if (size > 0) {
 		switch(buf[0]) {
 		case 'Y':
-- 
2.49.0