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

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Message-ID: <2526100.mKikVBQdmv@sven-l14>
Date:   Sun, 24 Oct 2021 16:58:30 +0200
From:   Sven Eckelmann <sven@...fation.org>
To:     mareklindner@...mailbox.ch, sw@...onwunderlich.de, a@...table.cc,
        davem@...emloft.net, kuba@...nel.org,
        Pavel Skripkin <paskripkin@...il.com>
Cc:     b.a.t.m.a.n@...ts.open-mesh.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pavel Skripkin <paskripkin@...il.com>,
        syzbot+28b0702ada0bf7381f58@...kaller.appspotmail.com
Subject: Re: [PATCH] net: batman-adv: fix error handling

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>


Kind regards,
	Sven
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