From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 2CD664C6D for ; Fri, 31 Oct 2025 10:35:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761906909; cv=none; b=P1t8NNkhQur2EJ5QdQweARP2CtsuEtX9PdunFGkqxmUbkuNPWRSkS45poKmRAQ9T8AwMKTamgL7z/SGu3l1VJ7WwzQSapwkAC/M2PK7cFKFRysDBcMMCkAmEcgDcjTMPEHF2mmuAcO4KS82tSM0jnMyRTUM6TQtZl4osNzjyPUg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761906909; c=relaxed/simple; bh=UQLJEn0L5U5fEjbo73zPZFZsVwvrPvxRKeocPtqgLW8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bGPgg2Sfuxfg86JjXJQAa+zt7T0TC0hI3sAr00mmJJo00IOrVrDNg64zQ2yc849pIPgsI5u025EU7WgZ01Nb0C1p5SmQ2cQDhYqRzzOeksO/T18Vfi4YYLuwQkGjUcbOKUwWddvBMAUnIFx0HQCP3w6o3olXClzwWSSslxRT+TE= 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=puzyI4VS; arc=none smtp.client-ip=91.218.175.189 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="puzyI4VS" Message-ID: <5adc0331-d699-402f-a798-acbf76e124db@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761906903; 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=15d5jagqZuWVPOYKHa4FJ77KmZ/Kk6K2xbbjYubxhkU=; b=puzyI4VSEcGnkKbWUyQwU8Fr2Cmzx93J3JXvaM/b5q6xIf6hFk4D9XEQIXtewTZydWzo3h N7MZfd9y7CNsoHOwLv1jNmWQyvU1MkeMbx+/edLqwHblPKh1suHNw5L5WZsFOSgk+13cso XTQeEKURcNDUydqbFINmNPex8s5BQEM= Date: Fri, 31 Oct 2025 18:34:58 +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 Content-Language: en-US To: Lorenzo Stoakes Cc: akpm@linux-foundation.org, big-sleep-vuln-reports@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, david@redhat.com, stable@vger.kernel.org, Mike Rapoport References: <20251031091818.66843-1-lance.yang@linux.dev> <02caf80d-ccde-49d4-99dd-0ea3763a0593@lucifer.local> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <02caf80d-ccde-49d4-99dd-0ea3763a0593@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/10/31 18:24, Lorenzo Stoakes wrote: > Small thing, sorry to be a pain buuuut could we please not send patches > in-reply to another mail, it makes it harder for people to see :) > > On Fri, Oct 31, 2025 at 11:59:16AM +0200, 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: >> >> 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) > > Agree with David, Mike this looks 'obviously correct' thanks for addressing > it. > > But also as per Mike, please update message accordingly and send v2 > not-in-reply-to-anything :P Sure. V2 is on the way ;) > > With that said: > > Reviewed-by: Lorenzo Stoakes 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 >>> >> >> -- >> Sincerely yours, >> Mike.