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 069FA1DDC38; Fri, 12 Jun 2026 06:48:00 +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=1781246881; cv=none; b=S/hoKo1R6BAq9QAEtP9bzxcoQ9KZqIqVGaoD1cQgFni09+BrjYuVBHCDi7YtAf8ym6BTyxXYO+cyOQgBUuWRUnP+IhyNZ3qXXj/QvAFTlodBR31UOmqb7l014Y4e6NaKBQWCXXdeuOI1BQ8rEMjr7z8Zl/C7tiFGJdxIyYivXYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781246881; c=relaxed/simple; bh=FF+cw+CNSSNDRA9Was9F2hF2dvZAVfbX7TDinDXXC5k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=koA0o0TktzMIAS4uRZVVQJ8eWBYDmsQM8TsZqmSoGe58O5bR/xucAPEUd5gYF4aJcPeCnFr6q0+xFntsL7KyzvjIW9gC36VxMBqGsZyMIP9tkv0TeuF+/AKuwzleCDqll5YO43L/hSHnC2P/8hYAaMR5UzjgR+6X++gRLVLtbV0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZYA1nWDv; 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="ZYA1nWDv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 797EA1F000E9; Fri, 12 Jun 2026 06:47:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781246880; bh=PYKn3nqZTI2tONzA/mOunAmSCw2g+cgo26Rk9W8RKAY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZYA1nWDv5Kwx1F24wjee8yzwFfyzxfMG+g8cWzvDB3bEUM+EMfkYHp6ABVQ9fRMRd T5YaKhfOZpYQjxQU55MBSKLYilBqhXMvNrhHHGQz0r5o04LvFzqj1rNcrziQdVjqP5 mgtT8FWQIY1P31vj/uykTfWkQu0gBpfZw99wjX6jGNrUV2PDEYvnBtoqU3CySIrALy c0uK5vi5VyyvoR4M61Fey8iKtYLRqwIN9V4ezzbThVuHfPlSWKV9B5KcQUd5VfJtEf LhU0zo6Whc6grmxDSJ4nryzfJ1hJZmrVx0NeoenuHrCQEF05auuoCz8/cxxtl4d03M Q5Rw7oS+Las7Q== Message-ID: <884cf1df-2256-4eb9-a2cb-67377a3bd8f6@kernel.org> Date: Fri, 12 Jun 2026 08:47:55 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup_test: fix race with PIN_LONGTERM_TEST ioctls To: John Hubbard , Yunhui Cui , akpm@linux-foundation.org, jgg@ziepe.ca, peterx@redhat.com, yang.lee@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org References: <20260608025043.88087-1-cuiyunhui@bytedance.com> <932e1fa0-dd9e-47d2-9133-d3b2f78dcd97@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/12/26 06:20, John Hubbard wrote: > On 6/7/26 7:50 PM, Yunhui Cui wrote: >> The PIN_LONGTERM_TEST helpers keep their state in global variables that >> are protected by pin_longterm_test_mutex when accessed from ioctl(). >> However, gup_test_release() calls pin_longterm_test_stop() without >> holding that mutex. >> >> This can race with PIN_LONGTERM_TEST_STOP and let two callers operate on >> the same pages array concurrently, corrupting the test state and possibly >> freeing it twice: > > Let's add here that there are *no* such callers in the kernel, today. > >> >> CPU 0 CPU 1 >> ----- ----- >> ioctl(PIN_LONGTERM_TEST_STOP) >> mutex_lock(&pin_longterm_test_mutex) >> pin_longterm_test_stop() >> if (pin_longterm_test_pages) >> kvfree(pin_longterm_test_pages) >> >> close() >> gup_test_release() >> pin_longterm_test_stop() >> if (pin_longterm_test_pages) >> kvfree(pin_longterm_test_pages) >> >> pin_longterm_test_pages = NULL >> mutex_unlock(&pin_longterm_test_mutex) >> >> Protect the release path with the same mutex so that stop and release >> cannot run pin_longterm_test_stop() concurrently. >> >> Fixes: c77369b437f9 ("mm/gup_test: start/stop/read functionality for PIN LONGTERM test") >> Cc: stable@vger.kernel.org > > umm, no, to "Cc: stable". This is the sort of thing that gives AI > a bad name. Specifically: > > * Nothing in tree can possibly hit this race condition. > > * This fix is purely static code analysis hygiene: correcting > a theoretical problem that does not actually provide any > sort of vulnerability fix in the kernel. > Yes, all rather useless churn that consumes our capacity. -- Cheers, David