From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Date: Tue, 31 Aug 2021 17:01:58 +0100 Subject: [Cluster-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl() In-Reply-To: References: <20210827164926.1726765-6-agruenba@redhat.com> Message-ID: List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, Aug 31, 2021 at 03:28:57PM +0000, Al Viro wrote: > On Tue, Aug 31, 2021 at 02:54:50PM +0100, Catalin Marinas wrote: > > > An arm64-specific workaround would be for pagefault_disable() to disable > > tag checking. It's a pretty big hammer, weakening the out of bounds > > access detection of MTE. My preference would be a fix in the btrfs code. > > > > A btrfs option would be for copy_to_sk() to return an indication of > > where the fault occurred and get fault_in_pages_writeable() to check > > that location, even if the copying would restart from an earlier offset > > (this requires open-coding copy_to_user_nofault()). An attempt below, > > untested and does not cover read_extent_buffer_to_user_nofault(): > > Umm... There's another copy_to_user_nofault() call in the same function > (same story, AFAICS). Yeah, I was too lazy to do it all and I don't have a setup to test the patch quickly either. BTW, my hack is missing an access_ok() check. I wonder whether copy_{to,from}_user_nofault() could actually return the number of bytes left to copy, just like their non-nofault counterparts. These are only used in a few places, so fairly easy to change. If we go for a btrfs fix along the lines of my diff, it saves us from duplicating the copy_to_user_nofault() code. -- Catalin