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Mon, 12 Feb 2024 05:28:36 -0800 (PST) Date: Mon, 12 Feb 2024 05:28:36 -0800 In-Reply-To: <3281463.44csPzL39Z@ripper> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <00000000000042c47206112f4123@google.com> Subject: Re: [syzbot] [batman?] BUG: soft lockup in sys_sendmsg From: syzbot 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 Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: VETPN3EFWICBLCOAUAQBC76YTCQISRXX X-Message-ID-Hash: VETPN3EFWICBLCOAUAQBC76YTCQISRXX X-MailFrom: 3BB3KZQkbAJsNTUF5GG9M5KKD8.BJJBG9PN9M7JIO9IO.7JH@M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-b.a.t.m.a.n.lists.open-mesh.org-0; header-match-b.a.t.m.a.n.lists.open-mesh.org-1; header-match-b.a.t.m.a.n.lists.open-mesh.org-2; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.8 Precedence: list List-Id: The list for a Better Approach To Mobile Ad-hoc Networking Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: > 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 > 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 > --- > 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 >