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Hello,
I was looking at some ascii charts trying to interpret an untrusted string and
realized something. We have this test in audit_log_untrustedstring() in
audit.c:
if (*p == '"' || *p == ' ' || *p < 0x20 || *p > 0x7f) {
It turns out that space is hex 20. So we could have:
if (*p == '"' || *p < 0x21 || *p > 0x7f) {
and have one less compare in that loop.
-Steve
On Mon, 2005-05-16 at 16:36 -0400, Steve Grubb wrote:
I was looking at some ascii charts trying to interpret an untrusted
string and
realized something. We have this test in audit_log_untrustedstring() in
audit.c:
if (*p == '"' || *p == ' ' || *p < 0x20 || *p > 0x7f) {
It turns out that space is hex 20. So we could have:
if (*p == '"' || *p < 0x21 || *p > 0x7f) {
and have one less compare in that loop.
Look at the assembly code. If that change actually does give us one
fewer compare, then file a GCC bug.
Given that it's already upstream, we might as well leave it the way it
is. As it is, it clearly documents the fact that a space is going to
cause the string to be quoted.
--
dwmw2
On Wednesday 18 May 2005 05:49, David Woodhouse wrote:
Look at the assembly code. If that change actually does give us one
fewer compare, then file a GCC bug.
I'd never expect gcc to do that kind of optimization. I have no intention of
taking this up with gcc maintainers at this time. We have a goal of getting
this code ready soon and I don't want to wait for them. The resulting
assembler is 17% shorter.
Given that it's already upstream, we might as well leave it the
way it
is. As it is, it clearly documents the fact that a space is going to
cause the string to be quoted.
Documentation is why we have comments. Do you want me to send a patch?
-Steve
On Wed, 2005-05-18 at 08:15 -0400, Steve Grubb wrote:
I'd never expect gcc to do that kind of optimization. I have no
intention of
taking this up with gcc maintainers at this time.
I would expect it though, and it takes only a moment to "take it up with
gcc maintainers" by mentioning it on IRC. Jakub confirms that GCC
_ought_ to get it right, and asked me to file a bug:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
> Given that it's already upstream, we might as well leave it
the way it
> is. As it is, it clearly documents the fact that a space is going to
> cause the string to be quoted.
Documentation is why we have comments. Do you want me to send a patch?
No, it's OK. Since I'm reordering and merging patches anyway, it's easy
enough to change it.
--
dwmw2
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Steve Grubb