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 D3C2E303A06; Fri, 31 Oct 2025 21:58:50 +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=1761947931; cv=none; b=MSAcF8BEb/zaDkFfuH/LP5nFnZI+VMRj98axAezz0/URKNfhAG5DayNjOM6VUU6Vae8oilox9f+BvFJa5P85Wg0fEXY54EF+7VT/RfcVX648s52OCKSbTexoWIdRMBUym/FBJiZuIVT3tMOVSW4dr5GFiUuPLY8xAarlHaLJe60= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761947931; c=relaxed/simple; bh=/cvZzBpFeVRkAE4Xx16DRajzLv/fquS5fXtcC3cFVUQ=; h=Date:To:From:Subject:Message-Id; b=MBRIb9brM8zYCVcrxunn5DG1bTpr5B22w86gFx7rJ/0YS1ajqZKGDArHbXvTbEa7Etf7LTUxg2fQlA6TfTUHUO/5ZQSViE6UE/3pt60WSoCJ+jKZ/rKcfxlRTUSSFEJJFlh2f+ttjicxprqylhScem40HMpp4eDVOD+npdZ2raM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=NlYYwgd9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="NlYYwgd9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 840A6C4CEE7; Fri, 31 Oct 2025 21:58:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1761947930; bh=/cvZzBpFeVRkAE4Xx16DRajzLv/fquS5fXtcC3cFVUQ=; h=Date:To:From:Subject:From; b=NlYYwgd9gCmXZ/IJ5pXlbTiLq0FFnWKi+bW6N1mJUvnKYV//4soFB6lsJe2zdXDh9 tpbLfa7ERpRDFA4KgEV6Gtjl2LW1jm64/aLGX5VXfLFAPJyw21883oPCwY28IiwauZ qjCyvh1ZaS3JmxIkAMcbHqeYghDLHaP4DY4B0H3Y= Date: Fri, 31 Oct 2025 14:58:49 -0700 To: mm-commits@vger.kernel.org,willy@infradead.org,stable@vger.kernel.org,rppt@kernel.org,lorenzo.stoakes@oracle.com,david@redhat.com,big-sleep-vuln-reports@google.com,lance.yang@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-secretmem-fix-use-after-free-race-in-fault-handler.patch added to mm-hotfixes-unstable branch Message-Id: <20251031215850.840A6C4CEE7@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/secretmem: fix use-after-free race in fault handler has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-secretmem-fix-use-after-free-race-in-fault-handler.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-secretmem-fix-use-after-free-race-in-fault-handler.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Lance Yang Subject: mm/secretmem: fix use-after-free race in fault handler Date: Fri, 31 Oct 2025 20:09:55 +0800 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 direct map before the folio is freed. Link: https://lkml.kernel.org/r/20251031120955.92116-1-lance.yang@linux.dev Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas") Signed-off-by: Lance Yang Reported-by: Google Big Sleep Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKrdQJ-ATdg@mail.gmail.com/ Acked-by: David Hildenbrand Reviewed-by: Mike Rapoport (Microsoft) Reviewed-by: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Signed-off-by: Andrew Morton --- mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/secretmem.c~mm-secretmem-fix-use-after-free-race-in-fault-handler +++ a/mm/secretmem.c @@ -82,13 +82,13 @@ retry: __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; _ Patches currently in -mm which might be from lance.yang@linux.dev are mm-secretmem-fix-use-after-free-race-in-fault-handler.patch mm-khugepaged-guard-is_zero_pfn-calls-with-pte_present.patch