From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 F26DE1AF0A6; Tue, 21 Jan 2025 20:50:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737492657; cv=none; b=rPsVsTwgH5PQAGkV+2pX5FkMJNX2xnK7RN0ZA1Eu6rttac7Ut4/hO2YgaPyRltnABPENdrFgwXCGuiL+XRqsewwziR19qfhY8C/CAO1/xn7JF4Ve0A/995wBzAoCLsaWFyeajR0gHlzC2Mdm8W/yuQQIYVGn6v5Z+Y+lV9q881I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737492657; c=relaxed/simple; bh=L4QsSvUNTuj/BD8oDyelC4osbKQ4lwJhci9EGZVvoDQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=tcq4GPl3cVoPEoUZ7nTC7W+lIbgtTIcRt3cX1uoAIXhhRZxXcJrquvzUU+Obzv1eYP8IuCAIhUql8KuttAG5TzVJLaLPU7ia7hRZdR+RHJo/W18ABSUYXCsJiSEZcvkYTBksPqwhWMX8s7KLcBThwGrZmj57Bm6XIxNbZj01E8I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ut/up3/q; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ut/up3/q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A629C4CEDF; Tue, 21 Jan 2025 20:50:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737492656; bh=L4QsSvUNTuj/BD8oDyelC4osbKQ4lwJhci9EGZVvoDQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ut/up3/qCL5+kpEcZu+6sJacaOho45ONUGysrLO7ExFJi3N3heGvo3bAp8wY5iSzh ngOdHngWnWDfutwjZeSE/D0Fbu5RHmJm9fYMQRvqzv3+6eXav1k39tyV0yFFZSVp9C Q+VcKfGOK9S1L8pd3IrbOSDb4YdSVKWZCNxN5Uag7N5SJHVfEiPiUnXTN6O2f21Am0 oTNdsjQV+mpuvZEXtvPhRIhQyaVCKV2dEob/fTzMNLYKcJmm2o66SFN7F2VQyoLvdy gJhEhzBdiswEVbrex3q/I0iFlTvwGY0Ycstqn6/4zKAClPPO60pW+eJXgMuZWCGhqY 2jTkuiUvdZxGQ== Message-ID: <6fb21e60487273864136b4912951b5a4fb5b3ae0.camel@kernel.org> Subject: Re: [PATCH] nfsd: free nfsd_file by gc after adding it to lru list From: Jeff Layton To: Chuck Lever , Li Lingfeng , neilb@suse.de, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai1@huaweicloud.com, houtao1@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, lilingfeng@huaweicloud.com Date: Tue, 21 Jan 2025 15:50:53 -0500 In-Reply-To: References: <20250113025957.1253214-1-lilingfeng3@huawei.com> <8864761c99553a7f18adc13e98b4ef6255da1d9e.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-01-15 at 10:03 -0500, Chuck Lever wrote: > On 1/14/25 2:39 PM, Jeff Layton wrote: > > On Tue, 2025-01-14 at 14:27 -0500, Jeff Layton wrote: > > > On Mon, 2025-01-13 at 10:59 +0800, Li Lingfeng wrote: > > > > In nfsd_file_put, after inserting the nfsd_file into the nfsd_file_= lru > > > > list, gc may be triggered in another thread and immediately release= this > > > > nfsd_file, which will lead to a UAF when accessing this nfsd_file a= gain. > > > >=20 > > > > All the places where unhash is done will also perform lru_remove, s= o there > > > > is no need to do lru_remove separately here. After inserting the nf= sd_file > > > > into the nfsd_file_lru list, it can be released by relying on gc. > > > >=20 > > > > Fixes: 4a0e73e635e3 ("NFSD: Leave open files out of the filecache L= RU") > > > > Signed-off-by: Li Lingfeng > > > > --- > > > > fs/nfsd/filecache.c | 12 ++---------- > > > > 1 file changed, 2 insertions(+), 10 deletions(-) > > > >=20 > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > > > index a1cdba42c4fa..37b65cb1579a 100644 > > > > --- a/fs/nfsd/filecache.c > > > > +++ b/fs/nfsd/filecache.c > > > > @@ -372,18 +372,10 @@ nfsd_file_put(struct nfsd_file *nf) > > > > /* Try to add it to the LRU. If that fails, decrement. */ > > > > if (nfsd_file_lru_add(nf)) { > > > > /* If it's still hashed, we're done */ > > > > - if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > > > > + if (list_lru_count(&nfsd_file_lru)) > > > > nfsd_file_schedule_laundrette(); > > > > - return; > > > > - } > > > > =20 > > > > - /* > > > > - * We're racing with unhashing, so try to remove it from > > > > - * the LRU. If removal fails, then someone else already > > > > - * has our reference. > > > > - */ > > > > - if (!nfsd_file_lru_remove(nf)) > > > > - return; > > > > + return; > > > > } > > > > } > > > > if (refcount_dec_and_test(&nf->nf_ref)) > > >=20 > > > I think this looks OK. Filecache bugs are particularly nasty though, = so > > > let's run this through a nice long testing cycle. > > >=20 > > > Reviewed-by: Jeff Layton > >=20 > > Actually, I take it back. This is problematic in another way. > >=20 > > In this case, we're racing with another task that is unhashing the > > object, but we've put it on the LRU ourselves. What guarantee do we > > have that the unhashing and removal from the LRU didn't occur before > > this task called nfsd_file_lru_add()? That's why we attempt to remove > > it here -- we can't rely on the task that unhashed it to do so at that > > point. > >=20 > > What might be best is to take and hold the rcu_read_lock() before doing > > the nfsd_file_lru_add, and just release it after we do these racy > > checks. That should make it safe to access the object. > >=20 > > Thoughts? >=20 > Holding the RCU read lock will keep the dereferences safe since > nfsd_file objects are freed only after an RCU grace period. But will the > logic in nfsd_file_put() work properly on totally dead nfsd_file > objects? I don't see a specific failure mode there, but I'm not very > imaginative. >=20 > Overall, I think RCU would help. >=20 >=20 To be clear, I think we need to drop e57420be100ab from your nfsd- testing branch. The race I identified above is quite likely to occur and could lead to leaks. If Li Lingfeng doesn't propose a patch, I'll spin one up tomorrow. I think the RCU approach is safe. Thanks, --=20 Jeff Layton