netdev - Re: [PATCH] net: batman-adv: fix error handling

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Message-ID: <20211025174950.1bec22fb@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 25 Oct 2021 17:49:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sven Eckelmann <sven@...fation.org>, mareklindner@...mailbox.ch
Cc:     sw@...onwunderlich.de, a@...table.cc, davem@...emloft.net,
        Pavel Skripkin <paskripkin@...il.com>,
        b.a.t.m.a.n@...ts.open-mesh.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+28b0702ada0bf7381f58@...kaller.appspotmail.com
Subject: Re: [PATCH] net: batman-adv: fix error handling

On Sun, 24 Oct 2021 16:58:30 +0200 Sven Eckelmann wrote:
> On Sunday, 24 October 2021 15:13:56 CEST Pavel Skripkin wrote:
> > Syzbot reported ODEBUG warning in batadv_nc_mesh_free(). The problem was
> > in wrong error handling in batadv_mesh_init().
> > 
> > Before this patch batadv_mesh_init() was calling batadv_mesh_free() in case
> > of any batadv_*_init() calls failure. This approach may work well, when
> > there is some kind of indicator, which can tell which parts of batadv are
> > initialized; but there isn't any.
> > 
> > All written above lead to cleaning up uninitialized fields. Even if we hide
> > ODEBUG warning by initializing bat_priv->nc.work, syzbot was able to hit
> > GPF in batadv_nc_purge_paths(), because hash pointer in still NULL. [1]
> > 
> > To fix these bugs we can unwind batadv_*_init() calls one by one.
> > It is good approach for 2 reasons: 1) It fixes bugs on error handling
> > path 2) It improves the performance, since we won't call unneeded
> > batadv_*_free() functions.
> > 
> > So, this patch makes all batadv_*_init() clean up all allocated memory
> > before returning with an error to no call correspoing batadv_*_free()
> > and open-codes batadv_mesh_free() with proper order to avoid touching
> > uninitialized fields.
> > 
> > Link: https://lore.kernel.org/netdev/000000000000c87fbd05cef6bcb0@google.com/ [1]
> > Reported-and-tested-by: syzbot+28b0702ada0bf7381f58@...kaller.appspotmail.com
> > Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
> > Signed-off-by: Pavel Skripkin <paskripkin@...il.com>  
> 
> Acked-by: Sven Eckelmann <sven@...fation.org>

FWIW I'm marking this as "Awaiting upstream" in netdev patchwork,
please LMK if you prefer for it to be applied directly.