From: syzbot <syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com>
To: sven@narfation.org
Cc: a@unstable.cc, b.a.t.m.a.n@lists.open-mesh.org,
davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
linux-kernel@vger.kernel.org, mareklindner@neomailbox.ch,
netdev@vger.kernel.org, pabeni@redhat.com, sven@narfation.org,
sw@simonwunderlich.de, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [batman?] BUG: soft lockup in sys_sendmsg
Date: Mon, 12 Feb 2024 05:28:36 -0800 [thread overview]
Message-ID: <00000000000042c47206112f4123@google.com> (raw)
In-Reply-To: <3281463.44csPzL39Z@ripper>
> On Monday, 12 February 2024 11:26:24 CET syzbot wrote:
>> syzbot found the following issue on:
>>
>> HEAD commit: 41bccc98fb79 Linux 6.8-rc2
>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14200118180000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=451a1e62b11ea4a6
>> dashboard link: https://syzkaller.appspot.com/bug?extid=a6a4b5bb3da165594cff
>> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>> userspace arch: arm64
>>
>> Unfortunately, I don't have any reproducer for this issue yet.
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/0772069e29cf/disk-41bccc98.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/659d3f0755b7/vmlinux-41bccc98.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/7780a45c3e51/Image-41bccc98.gz.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com
>>
>
> #syz test
This crash does not have a reproducer. I cannot test it.
>
> From 5984ace8f8df7cf8d6f98ded0eebe7d962028992 Mon Sep 17 00:00:00 2001
> From: Sven Eckelmann <sven@narfation.org>
> Date: Mon, 12 Feb 2024 13:10:33 +0100
> Subject: [PATCH] batman-adv: Avoid infinite loop trying to resize local TT
>
> If the MTU of one of an attached interface becomes too small to transmit
> the local translation table then it must be resized to fit inside all
> fragments (when enabled) or a single packet.
>
> But if the MTU becomes too low to transmit even the header + the VLAN
> specific part then the resizing of the local TT will never succeed. This
> can for example happen when the usable space is 110 bytes and 11 VLANs are
> on top of batman-adv. In this case, at least 116 byte would be needed.
> There will just be an endless spam of
>
> batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (110)
>
> in the log but the function will never finish. Problem here is that the
> timeout will be halved in each step and will then stagnate at 0 and
> therefore never be able to reduce the table even more.
>
> There are other scenarios possible with a similar result. The number of
> BATADV_TT_CLIENT_NOPURGE entries in the local TT can for example be too
> high to fit inside a packet. Such a scenario can therefore happen also with
> only a single VLAN + 7 non-purgable addresses - requiring at least 120
> bytes.
>
> While this should be handled proactively when:
>
> * interface with too low MTU is added
> * VLAN is added
> * non-purgeable local mac is added
> * MTU of an attached interface is reduced
> * fragmentation setting gets disabled (which most likely requires dropping
> attached interfaces)
>
> not all of these scenarios can be prevented because batman-adv is only
> consuming events without the the possibility to prevent these actions
> (non-purgable MAC address added, MTU of an attached interface is reduced).
> It is therefore necessary to also make sure that the code is able to handle
> also the situations when there were already incompatible system
> configurations present.
>
> Cc: stable@vger.kernel.org
> Fixes: a19d3d85e1b8 ("batman-adv: limit local translation table max size")
> Reported-by: syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> net/batman-adv/translation-table.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
> index b95c36765d04..2243cec18ecc 100644
> --- a/net/batman-adv/translation-table.c
> +++ b/net/batman-adv/translation-table.c
> @@ -3948,7 +3948,7 @@ void batadv_tt_local_resize_to_mtu(struct net_device *soft_iface)
>
> spin_lock_bh(&bat_priv->tt.commit_lock);
>
> - while (true) {
> + while (timeout) {
> table_size = batadv_tt_local_table_transmit_size(bat_priv);
> if (packet_size_max >= table_size)
> break;
> --
> 2.39.2
>
next prev parent reply other threads:[~2024-02-12 13:28 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-12 10:26 [syzbot] [batman?] BUG: soft lockup in sys_sendmsg syzbot
2024-02-12 10:41 ` Eric Dumazet
2024-02-12 11:23 ` Sven Eckelmann
2024-02-12 13:28 ` Sven Eckelmann
2024-02-12 13:28 ` Sven Eckelmann
2024-02-12 13:28 ` syzbot [this message]
2024-03-21 18:26 ` [syzbot] [tipc?] " syzbot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=00000000000042c47206112f4123@google.com \
--to=syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com \
--cc=a@unstable.cc \
--cc=b.a.t.m.a.n@lists.open-mesh.org \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mareklindner@neomailbox.ch \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=sven@narfation.org \
--cc=sw@simonwunderlich.de \
--cc=syzkaller-bugs@googlegroups.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.