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Mon, 13 Jun 2022 02:57:19 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 13 Jun 2022 11:57:17 +0200 To: "Matthew Wilcox (Oracle)" Cc: Kees Cook , linux-mm@kvack.org, Uladzislau Rezki , Zorro Lang , linux-xfs@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 3/3] usercopy: Make usercopy resilient against ridiculously large copies Message-ID: References: <20220612213227.3881769-1-willy@infradead.org> <20220612213227.3881769-4-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220612213227.3881769-4-willy@infradead.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655114241; a=rsa-sha256; cv=none; b=01IhsUpR56S7wereyGgxkeq9CBE2ls9nOkOIPvVWGiOiHTR1pBCIxyhaKyFA7pl/cN991M 3TE/gDxmdTYnNTB/kSpK2FTwVhLBYoPUcHL7ky3JNMl8PpQlXEbJonFrHVrNo2rX9+F+yJ NaHSI0EwFHQmMmaK89TnSWBDzoUCVIQ= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=mSAZ9WOe; 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dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: huzj1qayee8beg31pe7ueed1sojtu7z5 X-HE-Tag: 1655114241-489717 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: > If 'n' is so large that it's negative, we might wrap around and mistakenly > think that the copy is OK when it's not. Such a copy would probably > crash, but just doing the arithmetic in a more simple way lets us detect > and refuse this case. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/usercopy.c | 19 +++++++++---------- > 1 file changed, 9 insertions(+), 10 deletions(-) > > diff --git a/mm/usercopy.c b/mm/usercopy.c > index 31deee7dd2f5..ff16083cf1c8 100644 > --- a/mm/usercopy.c > +++ b/mm/usercopy.c > @@ -162,20 +162,18 @@ static inline void check_heap_object(const void *ptr, unsigned long n, > bool to_user) > { > uintptr_t addr = (uintptr_t)ptr; > + unsigned long offset; > struct folio *folio; > > if (is_kmap_addr(ptr)) { > - unsigned long page_end = addr | (PAGE_SIZE - 1); > - > - if (addr + n - 1 > page_end) > - usercopy_abort("kmap", NULL, to_user, > - offset_in_page(ptr), n); > + offset = offset_in_page(ptr); > + if (n > PAGE_SIZE - offset) > + usercopy_abort("kmap", NULL, to_user, offset, n); > return; > } > > if (is_vmalloc_addr(ptr)) { > struct vmap_area *area = find_vmap_area(addr); > - unsigned long offset; > > if (!area) { > usercopy_abort("vmalloc", "no area", to_user, 0, n); > @@ -184,9 +182,10 @@ static inline void check_heap_object(const void *ptr, unsigned long n, > > /* XXX: We should also abort for free vmap_areas */ > > - offset = addr - area->va_start; > - if (addr + n > area->va_end) > + if (n > area->va_end - addr) { > + offset = addr - area->va_start; > usercopy_abort("vmalloc", NULL, to_user, offset, n); > + } > return; > } > > @@ -199,8 +198,8 @@ static inline void check_heap_object(const void *ptr, unsigned long n, > /* Check slab allocator for flags and size. */ > __check_heap_object(ptr, n, folio_slab(folio), to_user); > } else if (folio_test_large(folio)) { > - unsigned long offset = ptr - folio_address(folio); > - if (offset + n > folio_size(folio)) > + offset = ptr - folio_address(folio); > + if (n > folio_size(folio) - offset) > usercopy_abort("page alloc", NULL, to_user, offset, n); > } > } > -- > 2.35.1 > Looks good to me: Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki