From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 1E0AF336EEE for ; Fri, 31 Oct 2025 10:34:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761906865; cv=none; b=ZJ+2JHId8eGvPwZsAcVKQSPZJ5C2OCFiLPwNx8lkG5Dd9/GBuUnktFlSJgPHrrBV23Gz034oRuylr3isxnPjKKYYBafI1D2xIQ9pBbN83BpWvTKlFTgChk/6HSBUZw8gDvaicXgLQ30R8a9ngRMQ4O9xawa8YqU2zdWR85fqTMI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761906865; c=relaxed/simple; bh=DgOsns4eXsSGg4ImlNipqf7EsxEa/Phy3SMjBp8pzdc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nXC+vcEVYplRin08Fkg38uB+q7np6ZvtetIQJFdaQY9IZRn7Dt9jM1mKnN7jKMW9q/kZdXKW+Bs5ghTUBijn/jVIJPpMeYeryMtNCsEuv9XfwaHe0Z0bvBbg3/85hWU3tnLBdeWg5d1qR7/GQArDY15yM9DZ4VRVSRR7JdpDhHM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Nce8sMlE; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Nce8sMlE" Message-ID: <11c80527-5dc7-440f-b09e-a9e4a8093ee2@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761906850; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=No4nG0fxP+YGa8mecuIh966uI+UlF5o7DLaj/1/zRLQ=; b=Nce8sMlEtSshax3q44vCtydt5Q6Om6F3fG6V8IsPoi85c7l1X3hQpGwgjBtYRssoRogXiu s+3HlcOvHRTJKrKoZZIuo3lkykRBBW4X4ovuqyYo/Q17KmbE72Mt65pGhiRQEkew35cDsW +lY2qDo1vQSvh+PsnUGQSWVZvW3qM4Y= Date: Fri, 31 Oct 2025 18:34:02 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm/secretmem: fix use-after-free race in fault handler To: Mike Rapoport Cc: akpm@linux-foundation.org, big-sleep-vuln-reports@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, willy@infradead.org, david@redhat.com, stable@vger.kernel.org References: <20251031091818.66843-1-lance.yang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/10/31 17:59, Mike Rapoport wrote: > On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote: >> From: Lance Yang >> >> The error path in secretmem_fault() frees a folio before restoring its >> direct map status, which is a race leading to a panic. > > Let's use the issue description from the report: Will do. I'll also add the missing Fixes: tag. > > When a page fault occurs in a secret memory file created with > `memfd_secret(2)`, the kernel will allocate a new folio for it, mark > the underlying page as not-present in the direct map, and add it to > the file mapping. > > If two tasks cause a fault in the same page concurrently, both could > end up allocating a folio and removing the page from the direct map, > but only one would succeed in adding the folio to the file > mapping. The task that failed undoes the effects of its attempt by (a) > freeing the folio again and (b) putting the page back into the direct > map. However, by doing these two operations in this order, the page > becomes available to the allocator again before it is placed back in > the direct mapping. > > If another task attempts to allocate the page between (a) and (b), and > the kernel tries to access it via the direct map, it would result in a > supervisor not-present page fault. > >> Fix the ordering to restore the map before the folio is freed. > > ... restore the direct map > > With these changes > > Reviewed-by: Mike Rapoport (Microsoft) Thanks! Lance > >> >> Cc: >> Reported-by: Google Big Sleep >> Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKrdQJ-ATdg@mail.gmail.com/ >> Signed-off-by: Lance Yang >> --- >> mm/secretmem.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/secretmem.c b/mm/secretmem.c >> index c1bd9a4b663d..37f6d1097853 100644 >> --- a/mm/secretmem.c >> +++ b/mm/secretmem.c >> @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) >> __folio_mark_uptodate(folio); >> err = filemap_add_folio(mapping, folio, offset, gfp); >> if (unlikely(err)) { >> - folio_put(folio); >> /* >> * If a split of large page was required, it >> * already happened when we marked the page invalid >> * which guarantees that this call won't fail >> */ >> set_direct_map_default_noflush(folio_page(folio, 0)); >> + folio_put(folio); >> if (err == -EEXIST) >> goto retry; >> >> -- >> 2.49.0 >> >