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 E56E22D877E for ; Thu, 20 Nov 2025 19:26:57 +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=1763666818; cv=none; b=ggVfJh9vRXt4y3S44ZIjWg62IfOQLFwb+qKKWgz5HXWb2mmNTIAtTeN+LCa7JttsYDgFk6hAIJPjgp1FH8Vnwj/5WLtVgUXG2cE/YkyS/oglr+CFh2R4eGHQuqntm+hp4YoygLLdPuE6/qUBtm2uCbAUBcWNpVYj7DTm1Ufswv4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763666818; c=relaxed/simple; bh=S7ZcNDWKVU5QgJsDywWCTgoUisVhkPC7mbpUfOLQYus=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BQ47+k60ariC4rRO44aAWWEWwSK9Va64tp7hTTu1oGPeyJxMF8ftXyasznvquyQf+gl5Y6vCPcQB9HePMtcYW/rZroDZUURaWhMG7GZ5mk+BNAfsVLphyH2O+f59hBEeo93iyqd68UYvGrE3Srg83wx6jgz31fKhJyt0PM1VpzM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gWBQ3uw1; 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="gWBQ3uw1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D03EC116C6; Thu, 20 Nov 2025 19:26:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763666817; bh=S7ZcNDWKVU5QgJsDywWCTgoUisVhkPC7mbpUfOLQYus=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gWBQ3uw1Q52ONnhHCLK2s2BeoFf5LYv7ynK4067by6fFWthES1Ni6gNpzRn6DFAmv 5HfXSj327F0FeVHRmKdHyUvblXJY5IlElShSrrBkjESJRv692BjAaIjGC4gbaaYuJl aYxGiZ9KtUfJgSWV4RKYt4o6r5Gw8z1n3m6RNoDCzEcvV5fSyFAuV46M/A+D9L/zmy pQngN2LJz/Hvgew8UzzJDJaYGIDwz08CI86S3pgMb5kloMCkG2GG1BKh+EE/SC9SLU pj4+tQBET4a9nMM3XlZWLYvLcyAWSRhRj2qKqs2415gyxGs/+fFFrD0Jm/qv1/m/wc WhPxXMMG09pEA== 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 6.12.y] mm/secretmem: fix use-after-free race in fault handler Date: Thu, 20 Nov 2025 21:26:41 +0200 Message-ID: <20251120192641.2346018-1-rppt@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025112020-buddy-bobbed-3c5d@gregkh> References: <2025112020-buddy-bobbed-3c5d@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 4662f2510ae5..aec96e4896f0 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