netdev - Re: [PATCH] netfilter: ebtables: compat: fix a memory leak bug

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Message-ID: <CAAa=b7cwJ-2wPNtH_j6saHiUWRj7zSwzZ8sGPWfgG9AyxWrOPg@mail.gmail.com>
Date:   Mon, 22 Jul 2019 07:53:59 -0500
From:   Wenwen Wang <wenwen@...uga.edu>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:NETFILTER" <netfilter-devel@...r.kernel.org>,
        "open list:NETFILTER" <coreteam@...filter.org>,
        "moderated list:ETHERNET BRIDGE" <bridge@...ts.linux-foundation.org>,
        "open list:ETHERNET BRIDGE" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Wenwen Wang <wenwen@...uga.edu>
Subject: Re: [PATCH] netfilter: ebtables: compat: fix a memory leak bug

On Mon, Jul 22, 2019 at 7:34 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
>
> Nice catch.  The code that exists is confusing due to newinfo->entries
> being overwritten and then freed in the existing code path as you state
> in your commit log.
>
> * Wenwen Wang <wang6495@....edu> [190720 08:23]:
> > From: Wenwen Wang <wenwen@...uga.edu>
> >
> > In compat_do_replace(), a temporary buffer is allocated through vmalloc()
> > to hold entries copied from the user space. The buffer address is firstly
> > saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then
> > the entries in this temporary buffer is copied to the internal kernel
> > structure through compat_copy_entries(). If this copy process fails,
> > compat_do_replace() should be terminated. However, the allocated temporary
> > buffer is not freed on this path, leading to a memory leak.
> >
> > To fix the bug, free the buffer before returning from compat_do_replace().
> >
> > Signed-off-by: Wenwen Wang <wenwen@...uga.edu>
> > ---
> >  net/bridge/netfilter/ebtables.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> > index 963dfdc..fd84b48e 100644
> > --- a/net/bridge/netfilter/ebtables.c
> > +++ b/net/bridge/netfilter/ebtables.c
> > @@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user *user,
> >       state.buf_kern_len = size64;
> >
> >       ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state);
> > -     if (WARN_ON(ret < 0))
> > +     if (WARN_ON(ret < 0)) {
> > +             vfree(entries_tmp);
> >               goto out_unlock;
> > +     }
>
>
> Would it be worth adding a new goto label above out_unlock and free this
> entries_tmp?  It could then be used in previous failure path as well.

Yes, that would make the code much clearer and easier to understand.

Thanks!
Wenwen