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 DC6C32D877E for ; Thu, 20 Nov 2025 19:24:21 +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=1763666662; cv=none; b=rcrJxuuehmDl2lxToCHmYWEPK4Ob+RQuPTR1rkay2+Ebb/b/c07TOR+W5LEwItyOLfCy6Mtxn8/8Egttz8I9tDt5IuDfUiIla3S045xMV3EohiE4b6uBnvyxhvURLkYoQPbAjai6k0qidylUKxPc7CuwT5dB5nCuYK2jb5Yp9mc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763666662; c=relaxed/simple; bh=J5voABVOFUZMyXtGl3qGXlREOkEQU/wpwaWkFywlg5I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PQCZvYSjyigLUhw6Cbz2NBctHb8shtG/heXdP4Br4xpnxir32oGJrpDZZa5yLue0MHyDaqOVs6v1pRdVzIHSMxrEErZGUI8w4QeF6uZ0kPSKP8Lm8KYgr9BebH05D0zDi8GBknesyp2B2J5yjUZwEfTcwu2gjAe6MITNGHxYjNc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Jw6QLL+2; 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="Jw6QLL+2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 316FDC4CEF1; Thu, 20 Nov 2025 19:24:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763666661; bh=J5voABVOFUZMyXtGl3qGXlREOkEQU/wpwaWkFywlg5I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Jw6QLL+2VphYdQOeb89usYH2GuSUMxW0rY7+JlE+90hEJde550hziHuR6rOLZFGQk cSM/PhZFIBC0nT3iZNhavj1sz4cqId12iG+A+qCYmXOJQms2jN12PT41SO0CWHfxdn iAjYp1sG8swkjohdeZhP9Bgj+vkfDqCYFg60HMIYIXUBkUwN9tmIguQxmwg7QbrLwz Qw6J3vkaQdsfXFxzGRpOC+6EvxIgPgsXbDY+fl7fBUy+AB7/v0LqhncGLWe8kf5tFB yXya649VK1i8JKtUGszlRHFxnAKZRXUFsI90mMd1qnHD8wPn0SyJTL46PiAdyRpD1N AFR84u9c3UbuQ== From: Mike Rapoport To: stable@vger.kernel.org Cc: Mike Rapoport , Lance Yang , Google Big Sleep , David Hildenbrand , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Andrew Morton Subject: [PATCH 6.6.y] mm/secretmem: fix use-after-free race in fault handler Date: Thu, 20 Nov 2025 21:24:15 +0200 Message-ID: <20251120192415.2345459-1-rppt@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025112021-swept-idealness-9ecb@gregkh> References: <2025112021-swept-idealness-9ecb@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lance Yang 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 (cherry picked from commit 6f86d0534fddfbd08687fa0f01479d4226bc3c3d) Signed-off-by: Mike Rapoport (Microsoft) --- mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/secretmem.c b/mm/secretmem.c index 4bedf491a8a7..f64ea1cde2f9 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -84,13 +84,13 @@ 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(page); + folio_put(folio); if (err == -EEXIST) goto retry; -- 2.50.1