From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: Re: [PATCH v16 08/16] fs, arm64: untag user pointers in copy_mount_options Date: Fri, 7 Jun 2019 21:02:25 -0700 Message-ID: <201906072101.58C919E@keescook> References: <51f44a12c4e81c9edea8dcd268f820f5d1fad87c.1559580831.git.andreyknvl@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <51f44a12c4e81c9edea8dcd268f820f5d1fad87c.1559580831.git.andreyknvl@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Andrey Konovalov Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Catalin Marinas , Vincenzo Frascino , Will Deacon , Mark Rutland , Andrew Morton , Greg Kroah-Hartman , Yishai Hadas , Felix Kuehling , Alexander Deucher , Christian Koenig , Mauro Carvalho Chehab , Jens Wiklander List-Id: linux-rdma@vger.kernel.org On Mon, Jun 03, 2019 at 06:55:10PM +0200, Andrey Konovalov wrote: > This patch is a part of a series that extends arm64 kernel ABI to allow to > pass tagged user pointers (with the top byte set to something else other > than 0x00) as syscall arguments. > > In copy_mount_options a user address is being subtracted from TASK_SIZE. > If the address is lower than TASK_SIZE, the size is calculated to not > allow the exact_copy_from_user() call to cross TASK_SIZE boundary. > However if the address is tagged, then the size will be calculated > incorrectly. > > Untag the address before subtracting. > > Reviewed-by: Catalin Marinas > Signed-off-by: Andrey Konovalov One thing I just noticed in the commit titles... "arm64" is in the prefix, but these are arch-indep areas. Should the ", arm64" be left out? I would expect, instead: fs/namespace: untag user pointers in copy_mount_options Reviewed-by: Kees Cook -Kees > --- > fs/namespace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index b26778bdc236..2e85712a19ed 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2993,7 +2993,7 @@ void *copy_mount_options(const void __user * data) > * the remainder of the page. > */ > /* copy_from_user cannot cross TASK_SIZE ! */ > - size = TASK_SIZE - (unsigned long)data; > + size = TASK_SIZE - (unsigned long)untagged_addr(data); > if (size > PAGE_SIZE) > size = PAGE_SIZE; > > -- > 2.22.0.rc1.311.g5d7573a151-goog > -- Kees Cook