lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 1 Jun 2007 16:00:30 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Christoph Lameter <clameter@....com> cc: Andrew Morton <akpm@...ux-foundation.org>, Jeremy Fitzhardinge <jeremy@...p.org>, Srinivasa Ds <srinivasa@...ibm.com>, linux-kernel@...r.kernel.org, Srivatsa Vaddagiri <vatsa@...ibm.com>, Dinakar Guniguntala <dino@...ibm.com>, pj@....com, simon.derr@...l.net, clameter@...ulhu.engr.sgi.com, rientjes@...gle.com Subject: Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning On Fri, 1 Jun 2007, Christoph Lameter wrote: > > Right it could catch a lot of other bugs as well. I'd actually prefer "malloc(0)" to _not_ return NULL, but some known (non-NULL) bogus pointer. Why? Because it's quite sane to have simple logic like ptr = malloc(size); if (!ptr) return -ENOMEM; and writing it as if (size && !ptr) return -ENOMEM; is just annoying. Also, NULL is _special_. There are absolutely tons of code in the kernel (and elsewhere) that just does something *different* from NULL pointers, and that totally breaks the whole notion of "you can allocate a zero-sized allocation, you just must not dereference it". If people special-case NULL as something else, they won't even go through the normal code-path. So for *both* of the above reasons, it's actually stupid to return NULL for a zero-sized allocation. It would be much better to return another pointer that will trap on access. A good candidate might be to return #define BADPTR ((void *)16) which is a portable-enough (where "portable-enough" is "against strict ANSI C rules, but works in practice on all architectures") way to return something that will cause the same page fault behaviour as NULL, but will _not_ trigger the "NULL is special" code. (Of course, you then need to teach "kfree()" to accept it as another pointer to be ignored, that's fine). I bet you'd find *more* problems that way than by returning NULL, and you'd also avoid the whole problem with "if (!ptr) return -ENOMEM". Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists