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Mon, 08 May 2023 14:56:17 -0700 (PDT) MIME-Version: 1.0 References: <000000000000258e5e05fae79fc1@google.com> <20230507135844.1231056-1-lrh2000@pku.edu.cn> In-Reply-To: From: Pasha Tatashin Date: Mon, 8 May 2023 14:55:41 -0700 Message-ID: Subject: Re: usbdev_mmap causes type confusion in page_table_check To: Matthew Wilcox Cc: Ruihan Li , syzbot+fcf1a817ceb50935ce99@syzkaller.appspotmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: masus5doqennwj8kh4ynckurkxesjhbw X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 807CDC0003 X-Rspam-User: X-HE-Tag: 1683582978-656059 X-HE-Meta: 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 EF/Gni2E PAtV7sefYl8rtK1iPiSFGuu6au2xdE+fnR1q5+74usOfIl9LPQM80vZqYYOuQdIymM3ZEcsIOTr2yH5zLrOGrYOTAQUdT+GfLMe76xI/mN4d0Bj2cnp3WVGhyiRLmjTOeXdTWECom83Q5YrKkE2K7Mhw6bV4RLogrucsSVDpMxSLwE4gzVP5oD1EFFqd+nQBWLWFlyu73iouD4KRwHN6Uk+6yNJBmnT+rV4JshmBx0kGabcP81GqMM+8dlCK4vMAdA087f21M8Uq345ENTcXgYJLG2IaY1sRHyLjzIPj13hFAyqJ0xi7vFTkYq9Ozh+L6Jlxyq2nW4f+fRaHCzHwa4x+WPiMZLoEHJWH23fPcqTPiEnu+NAPG5EFJsKnIgDdeyABSMSIQwLbVXFRqUZD/et1MjQ== 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 Mon, May 8, 2023 at 2:52=E2=80=AFPM Matthew Wilcox = wrote: > > On Mon, May 08, 2023 at 02:48:59PM -0700, Pasha Tatashin wrote: > > On Mon, May 8, 2023 at 2:36=E2=80=AFPM Matthew Wilcox wrote: > > > > > > On Mon, May 08, 2023 at 05:27:10PM -0400, Pasha Tatashin wrote: > > > > > static void page_table_check_set(struct mm_struct *mm, unsigned l= ong addr, > > > > > unsigned long pfn, unsigned long= pgcnt, > > > > > bool rw) > > > > > { > > > > > // ... > > > > > anon =3D PageAnon(page); > > > > > for (i =3D 0; i < pgcnt; i++) { > > > > > // ... > > > > > if (anon) { > > > > > BUG_ON(atomic_read(&ptc->file_map_count))= ; > > > > > BUG_ON(atomic_inc_return(&ptc->anon_map_c= ount) > 1 && rw); > > > > > } else { > > > > > BUG_ON(atomic_read(&ptc->anon_map_count))= ; > > > > > BUG_ON(atomic_inc_return(&ptc->file_map_c= ount) < 0); > > > > > } > > > > > // ... > > > > > } > > > > > // ... > > > > > } > > > > > > > > > > This call to PageAnon is invalid for slab pages because slab reus= es the bits > > > > > in struct page/folio to store its internal states, and the anonym= ity bit only > > > > > exists in struct page/folio. As a result, the counters are incorr= ectly updated > > > > > and checked in page_table_check_set and page_table_check_clear, l= eading to the > > > > > bug being raised. > > > > > > > > We should change anon boolean to be: > > > > > > > > anon =3D !PageSlab(page) && PageAnon(page); > > > > > > No. Slab pages are not elegible for mapping into userspace. That's > > > > Sure, I can add BUG_ON(PageSlab(page)); to page_table_check_set. > > > > > all. There should be a BUG() for that. And I do mean BUG(), not > > > "return error to user". Something has gone horribly wrong, and it's > > > time to crash. > > > > It is just too easy to make slab available via remap_pfn_range(), but > > I do not think we want to add BUG() into the remap function, otherwise > > we will break devices such as /dev/mem. > > Slab pages can't be mmaped. Really, no matter what interface you're > using. page->_mapcount is necessarily incremented by mapping to > userspace, and slab uses that space for its own purposes (and has > for decades). It's similar for page tables and other allocations that > use PageType. Mapping random memory in /dev/mem can cause mapping slab pages in to userspace, the page->_mapcount is not incremented (and other fields are not accessed) in that case, as we are using VM_PFNMAP type VMA, which does not access "struct page". Pasha