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NFS: fix delegation_hash_table leak when nfs4_server_common_setup() fails

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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 <server>:/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: f5b3108e6a ("NFS: use a hash table for delegation lookup")
Cc: stable@vger.kernel.org
Signed-off-by: Nate Prodromou <nate@prodromou.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Nate Prodromou 2026-07-14 18:58:46 +00:00 committed by Trond Myklebust
parent 92a885576f
commit 2092f5b38f
1 changed files with 12 additions and 5 deletions
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17
fs/nfs/nfs4client.c
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@ -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;
}
/*