From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46498) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1adDOn-0002lX-T5 for qemu-devel@nongnu.org; Tue, 08 Mar 2016 03:53:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1adDOm-0006MN-TF for qemu-devel@nongnu.org; Tue, 08 Mar 2016 03:53:49 -0500 Date: Tue, 8 Mar 2016 16:53:37 +0800 From: Fam Zheng Message-ID: <20160308085337.GA26071@ad.usersys.redhat.com> References: <1457420446-25276-1-git-send-email-peterx@redhat.com> <1457420446-25276-3-git-send-email-peterx@redhat.com> <87twkhe6bm.fsf@blackfin.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87twkhe6bm.fsf@blackfin.pond.sub.org> Subject: Re: [Qemu-devel] [PATCH 2/8] block: fix unbounded stack for dump_qdict List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: Kevin Wolf , pbonzini@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, Peter Xu On Tue, 03/08 09:12, Markus Armbruster wrote: > Peter Xu writes: > > > Suggested-by: Paolo Bonzini > > CC: Markus Armbruster > > CC: Kevin Wolf > > CC: qemu-block@nongnu.org > > Signed-off-by: Peter Xu > > --- > > block/qapi.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/block/qapi.c b/block/qapi.c > > index db2d3fb..687e577 100644 > > --- a/block/qapi.c > > +++ b/block/qapi.c > > @@ -638,9 +638,12 @@ static void dump_qdict(fprintf_function func_fprintf, void *f, int indentation, > > QType type = qobject_type(entry->value); > > bool composite = (type == QTYPE_QDICT || type == QTYPE_QLIST); > > const char *format = composite ? "%*s%s:\n" : "%*s%s: "; > > Unrelated to your patch: ugh! > > Printf formats should be literals whenever possible, to make it easy for > the compiler to warn you when you screw up. It's trivially possible > here! Instead of > > func_fprintf(f, format, indentation * 4, "", key); > > do > > func_fprintf(f, "%*s%s:%c", indentation * 4, "", key, > composite ? '\n', ' ');; > > > - char key[strlen(entry->key) + 1]; > > +#define __KEY_LEN (256) > > + char key[__KEY_LEN]; > > int i; > > > > + assert(strlen(entry->key) + 1 <= __KEY_LEN); > > +#undef __KEY_LEN > > /* replace dashes with spaces in key (variable) names */ > > for (i = 0; entry->key[i]; i++) { > > key[i] = entry->key[i] == '-' ? ' ' : entry->key[i]; > > I'm afraid this isn't a good idea. It relies on the non-local argument > that nobody will ever put a key longer than 255 into a qdict that gets > dumped. That may even be the case, but you need to *prove* it, not just > assert it. The weakest acceptable proof might be assertions in every > place that put keys into a dict that might get dumped. I suspect that's > practical and maintainable only if there's a single place that does it. > > If this was a good idea, I'd recommend to avoid the awkward macro: Also I think the double underscore identifiers are considered reserved in C, no? > > char key[256]; > int i; > > assert(strlen(entry->key) + 1 <= ARRAY_SIZE(key)); > <...> Fam