[PATCH 01/19] nfs/localio: fix nfsd_file ref leak on nfs_local_doio() init failure

[Jeff Layton <jlayton@kernel.org>]

Two early return paths in nfs_local_doio() fail to release the localio
(nfsd_file) reference passed in by the caller:

- When hdr->args.count is zero, the function returns 0 without calling
  nfs_local_file_put().

- When nfs_local_iocb_init() fails (e.g. -ENOMEM from allocation or
  -EOPNOTSUPP if the file lacks read_iter/write_iter), the function
  returns the error without releasing localio or completing the hdr
  lifecycle.

A leaked nfsd_file pins the associated net namespace reference,
blocking network namespace teardown, and holds a reference on the
exported filesystem, preventing unmount.

Fix the zero-count path by adding the missing nfs_local_file_put()
call. Fix the iocb init failure path by jumping to a new cleanup label
that releases localio, sets hdr->task.tk_status, and calls
nfs_local_hdr_release() -- matching the existing error handling pattern
for the post-iocb error path.

Fixes: e77c464c31b3 ("nfs/nfsd: add "local io" support")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfs/localio.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index e55c5977fcc3..63cf6e2cc745 100644
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -970,12 +970,16 @@ int nfs_local_doio(struct nfs_client *clp, struct nfsd_file *localio,
 	struct nfs_local_kiocb *iocb;
 	int status = 0;
 
-	if (!hdr->args.count)
+	if (!hdr->args.count) {
+		nfs_local_file_put(localio);
 		return 0;
+	}
 
 	iocb = nfs_local_iocb_init(hdr, localio);
-	if (IS_ERR(iocb))
-		return PTR_ERR(iocb);
+	if (IS_ERR(iocb)) {
+		status = PTR_ERR(iocb);
+		goto out_put_localio;
+	}
 
 	switch (hdr->rw_mode) {
 	case FMODE_READ:
@@ -996,6 +1000,12 @@ int nfs_local_doio(struct nfs_client *clp, struct nfsd_file *localio,
 		nfs_local_hdr_release(hdr, call_ops);
 	}
 	return status;
+
+out_put_localio:
+	nfs_local_file_put(localio);
+	hdr->task.tk_status = status;
+	nfs_local_hdr_release(hdr, call_ops);
+	return status;
 }
 
 static void

-- 
2.54.0