NFSD: Guard admin state-revocation walks with NFSD_NET_UP

Writing to /proc/fs/nfsd/unlock_filesystem, or sending the
NFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPORT netlink command,
walks the NFSv4 client hash tables to revoke open state and cancel
async COPY operations.  All three handlers gate that walk on
nn->nfsd_serv, but a listener added via portlist or netlink
listener_set sets nn->nfsd_serv before any nfsd thread starts.
nfsd_startup_net() has not yet allocated nn->conf_id_hashtbl, so the
walkers dereference a NULL table.  A local administrator with
CAP_SYS_ADMIN can crash the kernel this way without ever starting the
server.

nn->nfsd_serv is set when the service is created, which precedes
table allocation.  NFSD_NET_UP instead brackets the window where the
tables are live: set at the end of nfsd_startup_net() and cleared in
nfsd_shutdown_net() after they are freed, both under nfsd_mutex.
Gating the three unlock paths on NFSD_NET_UP fixes the startup-time
NULL dereference while preserving the earlier post-shutdown
use-after-free fix.

Reported-by: XIAO WU <xiaowu.417@qq.com>
Fixes: 1ac3629bf012 ("nfsd: prepare for supporting admin-revocation of state")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260621162551.2469460-1-cel@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

0 files changed, 0 insertions, 0 deletions