From 92ea163c773cb4d0d5eaf103ed80c49d6758b96f Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Sat, 13 Jun 2026 18:16:33 -0400 Subject: [PATCH] NFSD: Prevent post-shutdown use-after-free in NFSD_CMD_UNLOCK_FILESYSTEM The NFSD_CMD_UNLOCK_FILESYSTEM netlink command runs nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before nn->nfsd_serv is confirmed set, the same pre-mutex ordering the procfs unlock_filesystem path carried. Once nfsd has shut down, nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the pointer intact, so the cancel helper iterates freed slab memory as an array of struct list_head and then dereferences a bogus nfs4_client when it takes clp->async_lock. A local administrator holding CAP_SYS_ADMIN can reach this use-after-free by stopping the server and then issuing the command. Move the async COPY cancel into the nfsd_mutex section, after nn->nfsd_serv is confirmed, so every NFSv4 state-table walker on this path observes a running server. Async copies exist only while the server runs, so gating the cancel on nn->nfsd_serv loses nothing. Fixes: 327c5168eff2 ("NFSD: Add NFSD_CMD_UNLOCK_FILESYSTEM netlink command") Cc: stable@vger.kernel.org Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260613-unlock-filesystem-uaf-v1-2-462b9bec8c84@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfsctl.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c index d0486f4a47ba..fa92e31d19d6 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -2340,14 +2340,15 @@ int nfsd_nl_unlock_filesystem_doit(struct sk_buff *skb, if (error) return error; - nfsd4_cancel_copy_by_sb(net, path.dentry->d_sb); error = nlmsvc_unlock_all_by_sb(path.dentry->d_sb); mutex_lock(&nfsd_mutex); - if (nn->nfsd_serv) + if (nn->nfsd_serv) { + nfsd4_cancel_copy_by_sb(net, path.dentry->d_sb); nfsd4_revoke_states(nn, path.dentry->d_sb); - else + } else { error = -EINVAL; + } mutex_unlock(&nfsd_mutex); path_put(&path);