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NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check

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The header for commit e75b23f9e3 ("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: e75b23f9e3 ("nfsd: check d_can_lookup in fh_verify of directories")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Link: https://patch.msgid.link/20260612191410.50177-1-snitzer@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Mike Snitzer
2026-06-12 15:14:10 -04:00
committed by Chuck Lever
parent 1507357a00
commit aa0cf48a44
1 changed files with 1 additions and 3 deletions
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4
fs/nfsd/nfsfh.c
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@@ -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) {