| 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
| ||
|
Message-ID: <CAABTaaBZfcoHTHKAEKtYv5no_52LpjCGpJg-6g+_=Wo9ftGi5g@mail.gmail.com>
Date: Tue, 14 Oct 2025 09:42:33 -0300
From: Ricardo Robaina <rrobaina@...hat.com>
To: Paul Moore <paul@...l-moore.com>
Cc: audit@...r.kernel.org, linux-kernel@...r.kernel.org, eparis@...hat.com
Subject: Re: [PATCH v1] audit: merge loops in __audit_inode_child()
On Mon, Oct 13, 2025 at 4:17 PM Paul Moore <paul@...l-moore.com> wrote:
>
> On Sep 4, 2025 Ricardo Robaina <rrobaina@...hat.com> wrote:
> >
> > Whenever there's audit context, __audit_inode_child() gets called
> > numerous times, which can lead to high latency in scenarios that
> > create too many sysfs/debugfs entries at once, for instance, upon
> > device_add_disk() invocation.
> >
> > # uname -r
> > 6.17.0-rc3+
> >
> > # auditctl -a always,exit -F path=/tmp -k foo
> > # time insmod loop max_loop=1000
> > real 0m42.753s
> > user 0m0.000s
> > sys 0m42.494s
> >
> > # perf record -a insmod loop max_loop=1000
> > # perf report --stdio |grep __audit_inode_child
> > 37.95% insmod [kernel.kallsyms] [k] __audit_inode_child
> >
> > __audit_inode_child() searches for both the parent and the child
> > in two different loops that iterate over the same list. This
> > process can be optimized by merging these into a single loop,
> > without changing the function behavior or affecting the code's
> > readability.
> >
> > This patch merges the two loops that walk through the list
> > context->names_list into a single loop. This optimization resulted
> > in around 54% performance enhancement for the benchmark.
> >
> > # uname -r
> > 6.17.0-rc3+-enhanced
> >
> > # auditctl -a always,exit -F path=/tmp -k foo
> > # time insmod loop max_loop=1000
> > real 0m19.388s
> > user 0m0.000s
> > sys 0m19.149s
> >
> > Signed-off-by: Ricardo Robaina <rrobaina@...hat.com>
> > ---
> > kernel/auditsc.c | 40 ++++++++++++++++++----------------------
> > 1 file changed, 18 insertions(+), 22 deletions(-)
>
> Thanks Ricardo, that's a nice improvement! I saw a few additional things
> that could help simplify the code and possibly speed things up a bit
> more, see my comments below.
>
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index eb98cd6fe91f..7abfb68687fb 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -2437,44 +2437,40 @@ void __audit_inode_child(struct inode *parent,
> > if (inode)
> > handle_one(inode);
> >
> > - /* look for a parent entry first */
> > list_for_each_entry(n, &context->names_list, list) {
> > - if (!n->name ||
> > - (n->type != AUDIT_TYPE_PARENT &&
> > - n->type != AUDIT_TYPE_UNKNOWN))
> > + /* can only match entries that have a name */
> > + if (!n->name)
> > continue;
> >
> > - if (n->ino == parent->i_ino && n->dev == parent->i_sb->s_dev &&
> > - !audit_compare_dname_path(dname,
> > - n->name->name, n->name_len)) {
> > + /* look for a parent entry first */
> > + if (!found_parent &&
> > + (n->type == AUDIT_TYPE_PARENT || n->type == AUDIT_TYPE_UNKNOWN) &&
> > + (n->ino == parent->i_ino && n->dev == parent->i_sb->s_dev &&
> > + !audit_compare_dname_path(dname, n->name->name, n->name_len))) {
> > if (n->type == AUDIT_TYPE_UNKNOWN)
> > n->type = AUDIT_TYPE_PARENT;
>
> We probably don't need to check 'n->type' first, as we want it to always
> be set to AUDIT_TYPE_PARENT regardless of it's current value.
>
> > found_parent = n;
>
> We can probably 'continue' here since a match can't be both a parent and
> a child at the same time.
>
> Similarly, if we add move the 'if (found_parent && found_child)' check
> up to here we don't need to run it on every pass through the loop, just
> when we find a match.
>
> Taking the two comment above into account, I would imagine something like
> this would good:
>
> found_parent = n;
> if (found_child)
> break;
> continue;
>
> > - break;
> > }
> > - }
> >
> > - cond_resched();
> > -
> > - /* is there a matching child entry? */
> > - list_for_each_entry(n, &context->names_list, list) {
> > - /* can only match entries that have a name */
> > - if (!n->name ||
> > - (n->type != type && n->type != AUDIT_TYPE_UNKNOWN))
> > - continue;
> > -
> > - if (!strcmp(dname->name, n->name->name) ||
> > - !audit_compare_dname_path(dname, n->name->name,
> > + /* is there a matching child entry? */
> > + if (!found_child &&
> > + (n->type == type || n->type == AUDIT_TYPE_UNKNOWN) &&
> > + (!strcmp(dname->name, n->name->name) ||
> > + !audit_compare_dname_path(dname, n->name->name,
> > found_parent ?
> > found_parent->name_len :
> > - AUDIT_NAME_FULL)) {
> > + AUDIT_NAME_FULL))) {
> > if (n->type == AUDIT_TYPE_UNKNOWN)
> > n->type = type;
> > found_child = n;
>
> Similar to the parent case above, let's check to see if both a parent and
> a child have been found. We can probably skip the 'continue' here are we
> are at the end of the loop.
>
> found_child = n;
> if (found_parent)
> break;
>
> > - break;
> > }
> > +
> > + if (found_parent && found_child)
> > + break;
> > }
> >
> > + cond_resched();
>
> The 'cond_resched()' call was located between the two loops to help avoid
> a soft lockup caused by running through both loops; since we are now
> condensing that into one loop we can probably drop the 'cond_resched()'
> call ... which is definitely a good thing as it was a bit of a hack, a
> necessary hack, but still a hack :)
>
> > if (!found_parent) {
> > /* create a new, "anonymous" parent record */
> > n = audit_alloc_name(context, AUDIT_TYPE_PARENT);
> > --
> > 2.51.0
>
> --
> paul-moore.com
>
Thank you for reviewing this one, Paul! And thanks a lot for your
suggestions, I'll work on a v2 addressing those shortly.
Powered by blists - more mailing lists