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 AEE9620013A; Tue, 14 Jan 2025 19:39:47 +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=1736883587; cv=none; b=JUoWX/NOjHinr26U9W5G9K+E28Hmvn33sQdtJA35NYiNznqrujMNeFZC1xG0aUBDpvFIwiOBwMR5AygJb4abvXoCiZg/JZ7/Rj6AkQSRJA7X5r6qpYYk+8Rz3zQzvZk+qjE7WeIwu8nGTN8k9D46s9F66m/87Y4LNJlgbQt7yYY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736883587; c=relaxed/simple; bh=Vou3AeUsPN6ylNTnMOdHzmfBBgDC277By/KKTN655LI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=RzXG7vEjQO6RjoK2FcXHJ+SCUXXk5zu9F7+h4XXGhhkmEMb1ToLgvmYByL6z7BM65G6L5973Mk8MZP4lUje2gXVKPBcZVsXg72Su7TrNdW/ovnG9DRUcdOw1XaHBEPkF+yW5k3qRZ2yZFvPvUxn+6ypa72WO5LFxHYs3cxGxlnY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=u0HLhw7k; 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="u0HLhw7k" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C6BCC4CEDD; Tue, 14 Jan 2025 19:39:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736883587; bh=Vou3AeUsPN6ylNTnMOdHzmfBBgDC277By/KKTN655LI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=u0HLhw7kZ1AtC+X3khyC3mfgxtsBRBWN8+820HEp5gX95bl6p6VgY1ZOQkDXn9Lt7 e47i58Ev/Pl68hEHWNx1GQEsHFU7vqeqTzCqc3ry5OuEDXRa3j0G9kAikmRzxzkjhB 7W9u7JF3ZlyIEdw1HgMcn+FxSv2P2BJoULreUEarRbwDx0y1PGLTTssz1GBxdHhGou WnScgPK+WlcO78i0JcLgr95AFA0rVicD8xvKela+EIYEF0UIzxv3A85D+0wvsAPI/2 GNs3KA6wMnIlY/K6oJF11qVfeCatqSUGSLJBdFdOAO9FlOmEeK+NTwtismYLbLiVeO XfR+qxtWDo6Cg== Message-ID: Subject: Re: [PATCH] nfsd: free nfsd_file by gc after adding it to lru list From: Jeff Layton To: Li Lingfeng , chuck.lever@oracle.com, 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, 14 Jan 2025 14:39:44 -0500 In-Reply-To: <8864761c99553a7f18adc13e98b4ef6255da1d9e.camel@kernel.org> 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 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 thi= s > > nfsd_file, which will lead to a UAF when accessing this nfsd_file again= . > >=20 > > All the places where unhash is done will also perform lru_remove, so th= ere > > is no need to do lru_remove separately here. After inserting the nfsd_f= ile > > 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 LRU") > > 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 Actually, I take it back. This is problematic in another way. 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. 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. Thoughts? --=20 Jeff Layton