[PATCH 1/2] NFS: Pin the 'struct nfs_server' during a FREE_STATEID call

[Anna Schumaker <anna@kernel.org>]

From: Anna Schumaker <anna.schumaker@hammerspace.com>

Dan Aloni reports that he was able to hit a use-after-free bug if a
FREE_STATEID operation gets delayed for whatever reason. Fix this by
bumping the refcount of the 'struct nfs_server' object for the duration
of the FREE_STATEID so it doesn't get cleaned up from underneath us
while operations are still in flight.

Reported-by: Dan Aloni <dan.aloni@vastdata.com>
Fixes: 7c1d5fae4a87 ("NFSv4: Convert nfs41_free_stateid to use an asynchronous RPC call")
Tested-by: Dan Aloni <dan.aloni@vastdata.com>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>
---
 fs/nfs/nfs4proc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index a3415082d610..3ad5ef52a2e8 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -10364,6 +10364,7 @@ static void nfs41_free_stateid_release(void *calldata)
 	struct nfs_free_stateid_data *data = calldata;
 	struct nfs_client *clp = data->server->nfs_client;
 
+	nfs_sb_deactive(data->server->super);
 	nfs_put_client(clp);
 	kfree(calldata);
 }
@@ -10405,6 +10406,10 @@ static int nfs41_free_stateid(struct nfs_server *server,
 
 	if (!refcount_inc_not_zero(&clp->cl_count))
 		return -EIO;
+	if (!nfs_sb_active(server->super)) {
+		nfs_put_client(clp);
+		return -EIO;
+	}
 
 	nfs4_state_protect(clp, NFS_SP4_MACH_CRED_STATEID,
 		&task_setup.rpc_client, &msg);
-- 
2.55.0