netdev - Re: [PATCH net] net/sched: cls_api: fix error handling causing NULL dereference

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Message-ID: <CA+ny2sz8+UFZtYFLEDo+VQrN3iEwSu_gG1+mKTWm4wL7PK+uTw@mail.gmail.com>
Date: Fri, 14 Feb 2025 15:38:24 +0100
From: Pierre Riteau <pierre@...ckhpc.com>
To: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net] net/sched: cls_api: fix error handling causing NULL dereference

On Fri, 14 Feb 2025 at 15:21, Pierre Riteau <pierre@...ckhpc.com> wrote:
>
> On Fri, 14 Feb 2025 at 13:46, Michal Swiatkowski
> <michal.swiatkowski@...ux.intel.com> wrote:
> >
> > On Thu, Feb 13, 2025 at 11:36:10PM +0100, Pierre Riteau wrote:
> > > tcf_exts_miss_cookie_base_alloc() calls xa_alloc_cyclic() which can
> > > return 1 if the allocation succeeded after wrapping. This was treated as
> > > an error, with value 1 returned to caller tcf_exts_init_ex() which sets
> > > exts->actions to NULL and returns 1 to caller fl_change().
> > >
> > > fl_change() treats err == 1 as success, calling tcf_exts_validate_ex()
> > > which calls tcf_action_init() with exts->actions as argument, where it
> > > is dereferenced.
> > >
> > > Example trace:
> > >
> > > BUG: kernel NULL pointer dereference, address: 0000000000000000
> > > CPU: 114 PID: 16151 Comm: handler114 Kdump: loaded Not tainted 5.14.0-503.16.1.el9_5.x86_64 #1
> > > RIP: 0010:tcf_action_init+0x1f8/0x2c0
> > > Call Trace:
> > >  tcf_action_init+0x1f8/0x2c0
> > >  tcf_exts_validate_ex+0x175/0x190
> > >  fl_change+0x537/0x1120 [cls_flower]
> > >
> > > Fixes: 80cd22c35c90 ("net/sched: cls_api: Support hardware miss to tc action")
> > > Signed-off-by: Pierre Riteau <pierre@...ckhpc.com>
> > > ---
> > >  net/sched/cls_api.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> > > index 8e47e5355be6..4f648af8cfaa 100644
> > > --- a/net/sched/cls_api.c
> > > +++ b/net/sched/cls_api.c
> > > @@ -97,7 +97,7 @@ tcf_exts_miss_cookie_base_alloc(struct tcf_exts *exts, struct tcf_proto *tp,
> > >
> > >       err = xa_alloc_cyclic(&tcf_exts_miss_cookies_xa, &n->miss_cookie_base,
> > >                             n, xa_limit_32b, &next, GFP_KERNEL);
> > > -     if (err)
> > > +     if (err < 0)
> > >               goto err_xa_alloc;
> > >
> > >       exts->miss_cookie_node = n;
> >
> > Thanks for fixing.
> > Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> >
> > The same thing is done in devlink_rel_alloc() (net/devlink/core.c). I am
> > not sure if it can lead to NULL pointer dereference as here.
> >
> > Thanks,
> > Michal
>
> Thanks for the review. I also checked other occurrences under net/ and
> wanted to investigate this one. It looks like it could produce a
> similar result.
>
> In devlink_rel_alloc(), if xa_alloc_cyclic() returns 1, we execute
> kfree(rel); return ERR_PTR(err);
> In caller devlink_rel_nested_in_add(), we would assign the value 1 to
> rel, check IS_ERR(rel) - which should be false? - and dereference rel
> at: rel->devlink_index = devlink->index;
>
> Should I update the patch to cover both issues?

Nevermind, I see you already posted a patch in the meantime. Thanks.