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

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Message-ID: <CA+ny2swxXoMheYQV=gf=P2bYhTzt0J3RhtOZz0++rem=jcq7dA@mail.gmail.com>
Date: Fri, 14 Feb 2025 15:21:50 +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 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?