From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-145.mta1.migadu.com [95.215.58.145]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E487F3783BE for ; Sun, 18 Oct 2026 06:16:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.145 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792304202; cv=none; b=bobOMtRd+tbzD+yJJjxv7tWwVde4Mm3bxsLdCSSWgcZrhKlyF9XHXRohm0M+VqS8bpug7fhy98sC9hNVW+RiQz0VkkRTbwjTJg77SajFnhC440ax4WGM3CVVFJ3b914TzaH1hT0tgOk4+9S3mgvWsNOJqKyC6wN76z2V3xkSyvs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792304202; c=relaxed/simple; bh=B7Gw/wiYK21i/cMa7GU1UmN3hJqv1WC6YvEMSTJM0Ps=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YerY5AX1hRgMnCt83cOYtzMmHeGNBwsarGju9OlCOoyYsSt/ZWp2aZEzaVkrjWZvEz4j9t0aq2WaAmcbWx19DkykmCMQdOxwRw8/TOJs3fNKXglroCk96i6XJ7TU6/ZJIOaP1vXQHw99mN/qlBwSn7Qisfy3aY9CIlk4m/Lik6s= 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=svOFuxEq; arc=none smtp.client-ip=95.215.58.145 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="svOFuxEq" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=B7Gw/wiYK21i/cMa7GU1UmN3hJqv1WC6YvEMSTJM0Ps=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1792304197; v=1; x=1792908997; b=svOFuxEqWf6TmVMdnsN1mZk98lR9tnesVti+KOrfgctxjpv8rBn12cxqNLDbHUyl+Rttw4Uy YA4lWw/9Qjlf9VWwziulrNT54f2eRyGnVA5cK41UhvKt5+6gNMuOUrAYCEmwdCUj8EoAzdj5nSU kH4lQrOX8B0Qk2jckfVlZGRU= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 8a974899a536c980; Sun, 18 Oct 2026 06:16:37 +0000 X-Mizu-Trace-ID: 8a974899a536c980 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, muchun.song@linux.dev, osalvador@suse.de, linmiaohe@huawei.com, nao.horiguchi@gmail.com, agl@us.ibm.com, mel@csn.ul.ie, riel@surriel.com, peterx@redhat.com, kas@kernel.org, rppt@kernel.org, josef@toxicpanda.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 02/10] mm/hugetlb: fix use-after-free of a new anon folio Date: Sun, 18 Oct 2026 14:16:32 +0800 Message-ID: <20261018061632.14622-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261015-urgent_fixes-v1-2-42796911043b@kernel.org> References: <20261015-urgent_fixes-v1-2-42796911043b@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Thu, Oct 15, 2026 at 06:07:08PM +0200, David Hildenbrand (Arm) wrote: >From: Josef Bacik > >For a fault in a private mapping with nothing in the page cache, >hugetlb_no_page() allocates a folio, locks it and maps it. The folio has >one reference, which belongs to the page table entry from then on. After >dropping the page table lock the function still sets the migratable flag >of the folio and unlocks it. > >Whoever zaps the entry in between frees the folio. The fault holds the >fault mutex and the lock of the vma. MADV_DONTNEED and the first unmap of >a hole punch, hugetlb_vmdelete_list(), do not take the fault mutex, and a >private vma only has a lock if it owns a reservation map: not with >MAP_NORESERVE, and not in the child after fork(). > >Then the flag is set in, and folio_unlock() is called on, a folio that is >free or has a new owner. A surplus page goes back to the page allocator >while it is locked: > > BUG: Bad page state in process init pfn:108e00 > flags: 0x200000000000059(locked|uptodate|dirty|head|node=0|zone=2) > page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > >A page of the pool can be given to the next user, of any file, who locks >it and loses the lock to the late folio_unlock(): > > kernel BUG at mm/filemap.c:1532! > hugetlb_no_page+0x111b/0x23e0 > hugetlb_fault+0x3a9/0x14a0 > >An unprivileged process is enough: threads that write to a MAP_PRIVATE | >MAP_NORESERVE hugetlb mapping, threads that call MADV_DONTNEED on it, and >one that takes the freed pages for another file. > >Until commit 3a47c54f09c4 ("hugetlbfs: revert use i_mmap_rwsem for more >pmd sharing synchronization") the fault held i_mmap_rwsem for reading, >which everybody who zaps takes for writing. The lock that commit >bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") gave >to private vmas closed the window again, but only for those with a >reservation map. > >Be done with the folio before the page table lock is dropped, as >hugetlb_wp() is with its copy. The function already unlocks page cache >folios under that lock. > >Original fix generated by an LLM and sent in private by Josef. > >Fixes: 3a47c54f09c4 ("hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization") >Cc: stable@vger.kernel.org >Signed-off-by: Josef Bacik >Reviewed-by: Lorenzo Stoakes (ARM) >[ david: simplify+move comment ] >Signed-off-by: David Hildenbrand (Arm) >--- Nice work! Nothing jumped out at me, so: Reviewed-by: Lance Yang