From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 22 Dec 2015 22:30:16 +0000 From: Al Viro Message-ID: <20151222223016.GC20997@ZenIV.linux.org.uk> References: <1450817041-21236-1-git-send-email-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: QUOTED-PRINTABLE In-Reply-To: <1450817041-21236-1-git-send-email-mic@digikod.net> Sender: linux-kernel-owner@vger.kernel.org Subject: Re: [PATCH] um: Fix pointer cast To: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= Cc: linux-kernel@vger.kernel.org, Jeff Dike , Richard Weinberger , Linus Torvalds , user-mode-linux-devel@lists.sourceforge.net List-ID: On Tue, Dec 22, 2015 at 09:44:01PM +0100, Micka=EBl Sala=FCn wrote: > Fix a pointer cast typo introduced in v4.4-rc5 especially visible for > the i386 subarchitecture where it results in a kernel crash. Why the hell bother casting it at all? _Any_ pointer will quietly conv= ert to void *, no typecasts needed. The second argument of copy_from_user is const void __user *; sc is struct sigcontext __user *sc, so &sb->oldmask is either __u32 __user * or __u64 __user *, for 32bit and 64bit builds resp. Either is assignment-compatible with const void __user *. Basically, cast is telling the typechecking logics "sod off, I know bet= ter". And here it's not needed at all. Moreover, the bug you are fixing here= is precisely that this code did *not* know better - if not for that cast, compiler would've immediately pointed to the problem. > - if (copy_from_user(&set.sig[0], (void *)sc->oldmask, sizeof(set.sig= [0])) || > + if (copy_from_user(&set.sig[0], (void *)&sc->oldmask, sizeof(set.si= g[0])) || Please, remove the cast completely. Simply pass it &sc->oldmask and be done with that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/