From 2092f5b38f88be306140c77aeeeb43fc1adacacc Mon Sep 17 00:00:00 2001 From: Nate Prodromou Date: Tue, 14 Jul 2026 18:58:46 +0000 Subject: [PATCH] NFS: fix delegation_hash_table leak when nfs4_server_common_setup() fails nfs4_server_common_setup() allocates server->delegation_hash_table first, but server->destroy - the only path that frees the table via nfs4_destroy_server() - is not assigned until the very end of the function. If any intermediate step fails (the is_ds_only_client() check, nfs4_init_session(), nfs4_get_rootfh(), or nfs_probe_server()), the function returns with server->destroy still NULL, so the caller's nfs_free_server() skips the destroy callback and the hash table is leaked (4 KiB per attempt with the default delegation watermark). This is trivially reachable from userspace: every failed NFSv4 mount leaks one allocation. A client that persistently retries a mount that cannot succeed leaks kernel memory without bound. Observed in production where a Longhorn backup poller retried mount.nfs4 against an NFSv3-only server roughly 10 times per second, leaking ~3.4 GiB of unreclaimable slab (kmalloc-rnd-13-4k) per day; the node accumulated 12 GiB of leaked slab before the source was identified via the kmem:kmalloc tracepoint (call_site=nfs4_delegation_hash_alloc). Reproducer: # server exports NFSv3 only (or export path absent for v4) while :; do mount -t nfs4 :/missing /mnt; done # watch SUnreclaim in /proc/meminfo grow 4 KiB per iteration Free the table on the error paths between the allocation and the assignment of server->destroy. Fixes: f5b3108e6a14 ("NFS: use a hash table for delegation lookup") Cc: stable@vger.kernel.org Signed-off-by: Nate Prodromou Reviewed-by: Christoph Hellwig Signed-off-by: Trond Myklebust --- fs/nfs/nfs4client.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c index d06bfe317890..b661f446ea49 100644 --- a/fs/nfs/nfs4client.c +++ b/fs/nfs/nfs4client.c @@ -917,20 +917,22 @@ static int nfs4_server_common_setup(struct nfs_server *server, return error; /* data servers support only a subset of NFSv4.1 */ - if (is_ds_only_client(server->nfs_client)) - return -EPROTONOSUPPORT; + if (is_ds_only_client(server->nfs_client)) { + error = -EPROTONOSUPPORT; + goto out_free_delegation_hash; + } /* We must ensure the session is initialised first */ error = nfs4_init_session(server->nfs_client); if (error < 0) - return error; + goto out_free_delegation_hash; nfs_server_set_init_caps(server); /* Probe the root fh to retrieve its FSID and filehandle */ error = nfs4_get_rootfh(server, mntfh, auth_probe); if (error < 0) - return error; + goto out_free_delegation_hash; dprintk("Server FSID: %llx:%llx\n", (unsigned long long) server->fsid.major, @@ -939,7 +941,7 @@ static int nfs4_server_common_setup(struct nfs_server *server, error = nfs_probe_server(server, mntfh); if (error < 0) - return error; + goto out_free_delegation_hash; nfs4_session_limit_rwsize(server); nfs4_session_limit_xasize(server); @@ -951,6 +953,11 @@ static int nfs4_server_common_setup(struct nfs_server *server, server->mount_time = jiffies; server->destroy = nfs4_destroy_server; return 0; + +out_free_delegation_hash: + kfree(server->delegation_hash_table); + server->delegation_hash_table = NULL; + return error; } /*