From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 942F8386423 for ; Thu, 9 Jul 2026 18:36:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783622168; cv=none; b=XZ48w8CBYCNtCM9u4MwaXVNUrCNUuTSevzIE4CHhULKGfiIs4dXID4YdjyMCUQ01vax0hBtIHCQf9ykxmaQjRPCBZedB2TU5f7hBd3aoK2gZ9CZwitP02ioZ/FHv6KxpKkKau5KHGxcFY2dkwy+PVg0Y1Fuzr2U2x2DE88cEKPk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783622168; c=relaxed/simple; bh=FVIAm01CfdlJ5jEL2vn6ahjGKE9D/xBfDzX3uQDUiFs=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=p5qP5AyyxP3LT7a+qDY9xK9H4dthTiZWXfOvjPasF9sKk2BYYe5Fpi2P1tk04pSpoAb0v/Q/5G46qE9F2Zna3wrEa/v9/nGP0xlKtpYXEfVhQo+yCVtWvSso16AcIPVgr7HXknuqgv5sDGAQ2fkCjtYUQUIB5+q87gjIJ9m36bk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Cinx6VM6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Cinx6VM6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B325C1F000E9; Thu, 9 Jul 2026 18:36:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783622167; bh=sf9gzQR3NmtrmyPDke/SBJteM0/7YSk5V3SdxfGRArM=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=Cinx6VM67SrkyfF0lQoQZRrqKQgdWBISHDlJ/6/WDPQX+6LYBziY2F20suDswcbGH x5fiCa3sKO/ngh3oWIONk9QsAHvgewwSpJqDtxQkXI3ejll4Bu+VI1xM4NemlIDAP9 dDPQZsi+JqqiGI3pW1FtG3uJYEnAMfZYhfWplW6wZ9jzJoRn6kcRu74MzrG0OCUzz8 vzn4044g5cM52umg64y7j2G5NmzQnC8xldE+1d3b5pyPCCVjlkCBABc9ccOoewnTuY z5Ve1si9Aw/5RhmUizKx7x+kLbZ5ogxiDZMnbvt46f7VROYv225yo00LAQVpSpXNzT /hTCeffIU264w== Message-ID: <075f2d2acaff6607f507ae1e2a47d1d6bd880dd2.camel@kernel.org> Subject: Re: [PATCH v4 7/9] NFSD: Prevent client use-after-free during blocked-lock reaping From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org Date: Thu, 09 Jul 2026 14:36:04 -0400 In-Reply-To: <20260709-cel-v4-7-1d519d9be0cb@kernel.org> References: <20260709-cel-v4-0-1d519d9be0cb@kernel.org> <20260709-cel-v4-7-1d519d9be0cb@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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only remaining reference a blocked lock on > nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but > no reference keeping the client alive. When the per-net laundromat > reaps such a lock, freeing the nbl drops the owner reference > held through flc_owner, and the final nfs4_put_stateowner() > takes the client's cl_lock. Because the laundromat detaches the > nbl first, __destroy_client() no longer finds it, so a concurrent > force_expire_client() can free the client before nfs4_put_stateowner() > runs, dereferencing cl_lock in freed memory. >=20 > Pin the client with cl_rpc_users before dropping > nn->blocked_locks_lock, and skip clients already expiring, whose > blocked locks __destroy_client() frees while holding an owner > reference. Take nn->client_lock outside nn->blocked_locks_lock. > Every other site holds nn->blocked_locks_lock as a leaf, acquiring > no further lock, so placing nn->client_lock outside it cannot form > a lock-order cycle. >=20 > Fixes: 7919d0a27f1e ("nfsd: add a LRU list for blocked locks") > Signed-off-by: Chuck Lever > --- > fs/nfsd/nfs4state.c | 23 ++++++++++++++++++++--- > 1 file changed, 20 insertions(+), 3 deletions(-) >=20 > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index 142ba7d80539..4acd02f1642c 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -357,6 +357,16 @@ free_blocked_lock(struct nfsd4_blocked_lock *nbl) > kref_put(&nbl->nbl_kref, free_nbl); > } > =20 > +/* A blocked lock's flc_owner is its nfs4_lockowner. */ > +static struct nfs4_client * > +nbl_client(struct nfsd4_blocked_lock *nbl) > +{ > + struct nfs4_lockowner *lo; > + > + lo =3D (struct nfs4_lockowner *)nbl->nbl_lock.c.flc_owner; > + return lo->lo_owner.so_client; > +} > + > static void > remove_blocked_locks(struct nfs4_lockowner *lo) > { > @@ -7591,22 +7601,29 @@ nfs4_laundromat(struct nfsd_net *nn) > * indefinitely once the lock does become free. > */ > BUG_ON(!list_empty(&reaplist)); > + spin_lock(&nn->client_lock); > spin_lock(&nn->blocked_locks_lock); > - while (!list_empty(&nn->blocked_locks_lru)) { > - nbl =3D list_first_entry(&nn->blocked_locks_lru, > - struct nfsd4_blocked_lock, nbl_lru); > + list_for_each_safe(pos, next, &nn->blocked_locks_lru) { > + nbl =3D list_entry(pos, struct nfsd4_blocked_lock, nbl_lru); > if (!state_expired(<, nbl->nbl_time)) > break; > + clp =3D nbl_client(nbl); > + if (is_client_expired(clp)) > + continue; > + atomic_inc(&clp->cl_rpc_users); > list_move(&nbl->nbl_lru, &reaplist); > list_del_init(&nbl->nbl_list); > } > spin_unlock(&nn->blocked_locks_lock); > + spin_unlock(&nn->client_lock); > =20 > while (!list_empty(&reaplist)) { > nbl =3D list_first_entry(&reaplist, > struct nfsd4_blocked_lock, nbl_lru); > + clp =3D nbl_client(nbl); > list_del_init(&nbl->nbl_lru); > free_blocked_lock(nbl); > + put_client_no_renew(clp); > } > #ifdef CONFIG_NFSD_V4_2_INTER_SSC > /* service the server-to-server copy delayed unmount list */ Reviewed-by: Jeff Layton