From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754135AbbCBXDs (ORCPT ); Mon, 2 Mar 2015 18:03:48 -0500 Received: from mail-la0-f41.google.com ([209.85.215.41]:45961 "EHLO mail-la0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbbCBXDp convert rfc822-to-8bit (ORCPT ); Mon, 2 Mar 2015 18:03:45 -0500 From: Rasmus Villemoes To: Andy Shevchenko Cc: Andrew Morton , Trond Myklebust , "J. Bruce Fields" , "David S. Miller" , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Organization: D03 References: <1422525801-26560-1-git-send-email-linux@rasmusvillemoes.dk> <1423525491-12613-1-git-send-email-linux@rasmusvillemoes.dk> <1423525491-12613-4-git-send-email-linux@rasmusvillemoes.dk> <1423571552.31903.468.camel@linux.intel.com> <87386dj4x0.fsf@rasmusvillemoes.dk> <1423578150.31903.480.camel@linux.intel.com> <87oaoo59n2.fsf@rasmusvillemoes.dk> <1424695820.14897.10.camel@linux.intel.com> <87k2z86xvs.fsf@rasmusvillemoes.dk> <1425299846.14897.124.camel@linux.intel.com> X-Hashcash: 1:20:150302:linux-nfs@vger.kernel.org::e/BLM8Ms8/LwDDrz:0000000000000000000000000000000000000NVQ X-Hashcash: 1:20:150302:trond.myklebust@primarydata.com::pqvDXhZSmciuem7/:00000000000000000000000000000009cV X-Hashcash: 1:20:150302:akpm@linux-foundation.org::5bGPgDF3kq+2MGBN:0000000000000000000000000000000000000ibe X-Hashcash: 1:20:150302:linux-kernel@vger.kernel.org::Wm7hoDHOHng6TPHf:00000000000000000000000000000000032qC X-Hashcash: 1:20:150302:andriy.shevchenko@linux.intel.com::ekDKmOS649M+QtK1:00000000000000000000000000003n47 X-Hashcash: 1:20:150302:netdev@vger.kernel.org::UxEWuEuUsMKURmN1:0000000000000000000000000000000000000004KaG X-Hashcash: 1:20:150302:bfields@fieldses.org::9819D6IL5eXKQvzO:000000000000000000000000000000000000000006TSz X-Hashcash: 1:20:150302:davem@davemloft.net::Eb2m3xX+j5Nq/q9Z:0000000000000000000000000000000000000000008Wrw Date: Tue, 03 Mar 2015 00:03:40 +0100 In-Reply-To: <1425299846.14897.124.camel@linux.intel.com> (Andy Shevchenko's message of "Mon, 02 Mar 2015 14:37:26 +0200") Message-ID: <87a8zvovcj.fsf@rasmusvillemoes.dk> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 02 2015, Andy Shevchenko wrote: > On Mon, 2015-02-23 at 23:55 +0100, Rasmus Villemoes wrote: >> On Mon, Feb 23 2015, Andy Shevchenko wrote: > >> > What about to make it a separate function *and* call from inside of >> > test_string_escape? Would it work for you? >> >> See my earlier point about "quite a lot of state to pass". But if this >> >> static __init void >> test_string_escape_overflow(const char *in, int p, char *out_real, int out_size, >> unsigned int flags, const char *esc, int q_test, >> const char *name) >> { >> int q_real; >> >> memset(out_real, 'Z', out_size); >> q_real = string_escape_mem(in, p, out_real, 0, flags, esc); >> if (q_real != q_test) >> pr_warn("Test '%s' failed: flags = %u, osz = 0, expected %d, got %d\n", >> name, flags, q_test, q_real); >> if (memchr_inv(out_real, 'Z', out_size)) >> pr_warn("Test '%s' failed: osz = 0 but string_escape_mem wrote to the buffer\n", >> name); >> } >> >> is what you want, sure, have it your way. > > Something like above, though might be few variables can be defined > inside it, such as out_real, out_size. Or maybe not at all: We could pass NULL, 0, which is what has to work anyway for the kasprintf case - failure will then be detected through an oops, but I think that should be ok. That would also remove the memset and memchr_inv calls above. I don't like the idea of just defining a small stack buffer (say buf[16]) and passing that (still with a size of 0): It's better to either detect writes directly (by passing a large enough buffer with known contents), or indirectly through an oops, as opposed to having to figure it out from random stack corruption. And kmalloc'ing+error handling+kfree'ing a buffer inside the overflow check would just be plain silly, when we have a large enough buffer already. >> I need to fix fs/proc/array.c in 3/3 as well, to make the kernel >> compile+boot and make the series bisectable. Before I send v4 please let >> me know what you think about this (the minimal fix I could come up with): >> >> diff --git a/fs/proc/array.c b/fs/proc/array.c >> index 1295a00ca316..20f2d50e2dba 100644 >> --- a/fs/proc/array.c >> +++ b/fs/proc/array.c >> @@ -99,10 +99,9 @@ static inline void task_name(struct seq_file *m, struct task_struct *p) >> buf = m->buf + m->count; >> >> /* Ignore error for now */ >> - string_escape_str(tcomm, &buf, m->size - m->count, >> - ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\"); >> + m->count += string_escape_str(tcomm, buf, m->size - m->count, >> + ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\"); > > Just a nitpick: what if we keep buf arithmetics in place, i.e. > buf += string_escape_str(); > m->count = … Yes, that will make the patch even smaller, just touching that single line. Done. > Also shouldn't we check if seq_overflow is set before even trying to > escape? Otherwise it will return something which is bigger that 0 and > advance m->count too far. I don't think we need to care. AFAICT, task_name is only used for /proc/*/status, and it is the first thing to fill anything into the seq_file, so overflow is impossible. [Testing for pre-existing overflow also wouldn't be enough; one should check whether there's actually room for ~32 bytes.] As I said, I do think that longer-term one shouldn't have to poke around in the seq_file internals, but for now I'd like to make the patch minimal. >> Another option is to do everything with a single seq_printf call, >> something like >> >> seq_printf(m, "Name:\t%*pEcs\n, (int)strlen(tcomm), tcomm) >> >> That will escape more than just \ and \n, but that would IMO be an >> improvement. But of course this is out of scope for this series.] > > It should be %pT and reconsider policy how we print task name in > different cases (vsprintf.c::comm_name()). Well, %pT is a completely new addition to vsprintf.c. Also, I don't think that would be a very good match - not every user of %pT might want escaping, so at the very least this would require implementing some extra flags for %pT. But if task_name would be the only user of those flags, I think the escaping logic is better kept there. Anyway, this is outside this series' scope. Rasmus