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imf30.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf30.hostedemail.com: domain of daniel@makrotopia.org designates 185.142.180.71 as permitted sender) smtp.mailfrom=daniel@makrotopia.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1676383253; a=rsa-sha256; cv=none; b=C2J7p1VwYSgulN40T9AyDRPZLg4jvT6Apdiy9cm2ElC12E6zAU58N33whuPhyu1Z60zGH4 ahjoMP59zTE6jbBaxELb30VInemET66zpF3nx8KKZNLEx9xuoHYZ6QLNwaCTP4OxcmyRhm KrFMBKxEXqTJduMTGJwcZrXU12HhIZI= Received: from local by fudo.makrotopia.org with esmtpsa (TLS1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.96) (envelope-from ) id 1pRvqg-0004pq-28; Tue, 14 Feb 2023 14:59:58 +0100 Date: Tue, 14 Feb 2023 13:59:49 +0000 From: Daniel Golle To: Greg Kroah-Hartman Cc: David Howells , Jens Axboe , Al Viro , Christoph Hellwig , Matthew Wilcox , Jan Kara , Jeff Layton , David Hildenbrand , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Guenter Roeck , Christoph Hellwig , John Hubbard , Miklos Szeredi , Hugh Dickins , Jan Harkes , Arnd Bergmann , coda@cs.cmu.edu, codalist@coda.cs.cmu.edu, linux-unionfs@vger.kernel.org Subject: Re: [PATCH v3 5/5] shmem, overlayfs, coda, tty, proc, kernfs, random: Fix splice-read Message-ID: References: <20230214083710.2547248-1-dhowells@redhat.com> <20230214083710.2547248-6-dhowells@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 66DCB80022 X-Stat-Signature: nikcm43gm3j4jyjzb54ytyape9iyyodz X-HE-Tag: 1676383252-63227 X-HE-Meta: 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 L23pxcXF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 14, 2023 at 09:54:08AM +0100, Greg Kroah-Hartman wrote: > On Tue, Feb 14, 2023 at 08:37:10AM +0000, David Howells wrote: > > The new filemap_splice_read() has an implicit expectation via > > filemap_get_pages() that ->read_folio() exists if ->readahead() doesn't > > fully populate the pagecache of the file it is reading from[1], potentially > > leading to a jump to NULL if this doesn't exist. > > > > A filesystem or driver shouldn't suffer from this if: > > > > - It doesn't set ->splice_read() > > - It implements ->read_folio() > > - It implements its own ->splice_read() > > > > Note that some filesystems set generic_file_splice_read() and > > generic_file_read_iter() but don't set ->read_folio(). g_f_read_iter() > > will fall back to filemap_read_iter() which looks like it should suffer > > from the same issue. > > > > Certain drivers, can just use direct_splice_read() rather than > > generic_file_splice_read() as that creates an output buffer and then just > > calls their ->read_iter() function: > > > > - random & urandom > > - tty > > - kernfs > > - proc > > - proc_namespace > > > > Stacked filesystems just need to pass the operation down a layer: > > > > - coda > > - overlayfs > > > > And finally, there's shmem (used in tmpfs, ramfs, rootfs). This needs its > > own splice-read implementation, based on filemap_splice_read(), but able to > > paste in zero_page when there's a page missing. > > > > Fixes: d9722a475711 ("splice: Do splice read from a buffered file without using ITER_PIPE") > > Signed-off-by: David Howells > > cc: Daniel Golle > > cc: Guenter Roeck > > cc: Christoph Hellwig > > cc: Jens Axboe > > cc: Al Viro > > cc: John Hubbard > > cc: David Hildenbrand > > cc: Matthew Wilcox > > cc: Miklos Szeredi > > cc: Hugh Dickins > > cc: Jan Harkes > > cc: Arnd Bergmann > > cc: Greg Kroah-Hartman > > cc: coda@cs.cmu.edu > > cc: codalist@coda.cs.cmu.edu > > cc: linux-unionfs@vger.kernel.org > > cc: linux-block@vger.kernel.org > > cc: linux-fsdevel@vger.kernel.org > > cc: linux-mm@kvack.org > > Link: https://lore.kernel.org/r/Y+pdHFFTk1TTEBsO@makrotopia.org/ [1] > > --- > > Acked-by: Greg Kroah-Hartman Confirming that the above indeed fixes the NULL pointer bug. Tested-by: Daniel Golle