From aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Fri, 12 Jun 2026 15:14:10 -0400 Subject: [PATCH] NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in fh_verify of directories") details the assumption that justified adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is invalid (in the case of NFS reexport). When NFSD exports an NFS filesystem it is very possible for nfsd_mode_check() to encounter a @dentry that doesn't have i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()). So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir return on that branch must stay. It guards the subsequent lookup_one_unlocked() -> __lookup_slow() path, which calls inode->i_op->lookup() with no NULL check, so returning nfserr_notdir is what keeps a client LOOKUP into such a @dentry from dereferencing a NULL method pointer. Fixes: e75b23f9e323 ("nfsd: check d_can_lookup in fh_verify of directories") Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer Link: https://patch.msgid.link/20260612191410.50177-1-snitzer@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfsfh.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c index b36915401758..ab53de1c280d 100644 --- a/fs/nfsd/nfsfh.c +++ b/fs/nfsd/nfsfh.c @@ -70,10 +70,8 @@ nfsd_mode_check(struct dentry *dentry, umode_t requested) if (requested == 0) /* the caller doesn't care */ return nfs_ok; if (mode == requested) { - if (mode == S_IFDIR && !d_can_lookup(dentry)) { - WARN_ON_ONCE(1); + if (mode == S_IFDIR && !d_can_lookup(dentry)) return nfserr_notdir; - } return nfs_ok; } if (mode == S_IFLNK) {