Forwarded: [PATCH] nfsd: fix percpu_ref leak when nfsd_net_up is false

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Subject: [PATCH] nfsd: fix percpu_ref leak when nfsd_net_up is false
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

When nfsd_destroy_serv() is called without any threads being started,
nfsd_startup_net() was never invoked, so nfsd_net_up remains false.

In this case, nfsd_shutdown_net() returns early without calling
percpu_ref_exit() to free the percpu reference initialized in
nfsd_create_serv().

This causes two memory leaks per call:
  - 8 bytes of percpu memory (the reference counter)
  - 64 bytes of slab memory (the percpu_ref_data structure)

Fix this by calling percpu_ref_exit() in the early return path when
nfsd_net_up is false.

Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
Fixes: 47e988147f40 ("nfsd: add nfsd_serv_try_get and nfsd_serv_put")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/nfsd/nfssvc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b08ae85d53ef..00c6a0c96885 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -406,8 +406,10 @@ static void nfsd_shutdown_net(struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	if (!nn->nfsd_net_up)
+	if (!nn->nfsd_net_up) {
+		percpu_ref_exit(&nn->nfsd_net_ref);
 		return;
+	}
 
 	percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
 	wait_for_completion(&nn->nfsd_net_confirm_done);
-- 
2.43.0