From 30c2df3005c99819e117402dc492db4a2a696c2f Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Tue, 2 Jun 2026 12:23:18 -0400 Subject: [PATCH] nfsd: fix refcount leak in nfsd_file_lru_add on insertion failure nfsd_file_lru_add() unconditionally increments nf_ref before attempting to insert the nfsd_file into the LRU via list_lru_add_obj(). If the insertion fails (the item is already linked), the incremented reference is never released, permanently inflating the refcount. The LRU shrinker callback (nfsd_file_lru_cb) uses refcount_dec_if_one() to reclaim entries, which requires nf_ref == 1. An inflated refcount therefore blocks eviction of the affected file cache entry for the lifetime of the nfsd instance. While this failure path is currently unreachable -- the sole caller in nfsd_file_do_acquire() operates on freshly-allocated objects that cannot already be on the LRU -- it represents a latent bug that would become exploitable if a future change adds another call site or alters the PENDING protocol. Fix this by: - Adding a compensating refcount_dec() on the failure path. Bare refcount_dec (rather than nfsd_file_put) is correct here because the caller in nfsd_file_do_acquire still holds its own construction reference, so the count goes from 2 back to 1 without risk of reaching zero. - Changing WARN_ON(1) to WARN_ON_ONCE(1) to prevent log flooding if this path is ever hit repeatedly. - Returning early on failure to skip the unnecessary call to nfsd_file_schedule_laundrette(), since no entry was added to the LRU. Fixes: 56221b42d717 ("nfsd: filecache: don't repeatedly add/remove files on the lru list") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260602-nfsd-testing-v2-6-e4ea62e3cd5c@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/filecache.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index 7f100c41022a..19beb4d482be 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -327,8 +327,11 @@ static void nfsd_file_lru_add(struct nfsd_file *nf) refcount_inc(&nf->nf_ref); if (list_lru_add_obj(&nfsd_file_lru, &nf->nf_lru)) trace_nfsd_file_lru_add(nf); - else - WARN_ON(1); + else { + refcount_dec(&nf->nf_ref); + WARN_ON_ONCE(1); + return; + } nfsd_file_schedule_laundrette(); }