Re: [syzbot] [batman?] BUG: soft lockup in sys_sendmsg

Eric Dumazet
2024-02-12T10:41:55Z

On Mon, Feb 12, 2024 at 11:26 AM syzbot
<syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> 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
>
> watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [syz-executor.0:28718]
> Modules linked in:
> irq event stamp: 45929391
> hardirqs last enabled at (45929390): [<ffff8000801d9dc8>] __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
> hardirqs last disabled at (45929391): [<ffff80008ad57108>] __el1_irq arch/arm64/kernel/entry-common.c:499 [inline]
> hardirqs last disabled at (45929391): [<ffff80008ad57108>] el1_interrupt+0x24/0x68 arch/arm64/kernel/entry-common.c:517
> softirqs last enabled at (2040): [<ffff80008002189c>] softirq_handle_end kernel/softirq.c:399 [inline]
> softirqs last enabled at (2040): [<ffff80008002189c>] __do_softirq+0xac8/0xce4 kernel/softirq.c:582
> softirqs last disabled at (2052): [<ffff80008aacbc40>] spin_lock_bh include/linux/spinlock.h:356 [inline]
> softirqs last disabled at (2052): [<ffff80008aacbc40>] batadv_tt_local_resize_to_mtu+0x60/0x154 net/batman-adv/translation-table.c:3949
> CPU: 1 PID: 28718 Comm: syz-executor.0 Not tainted 6.8.0-rc2-syzkaller-g41bccc98fb79 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : should_resched arch/arm64/include/asm/preempt.h:79 [inline]
> pc : __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:388
> lr : __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
> sp : ffff80009a0670b0
> x29: ffff80009a0670c0 x28: ffff70001340ce60 x27: ffff80009a0673d0
> x26: ffff00011e860290 x25: ffff0000d08a9f08 x24: 0000000000000001
> x23: 1fffe00023d4d3c1 x22: dfff800000000000 x21: ffff80008aacbf98
> x20: 0000000000000202 x19: ffff00011ea69e08 x18: ffff80009a066800
> x17: 77656e2074696620 x16: ffff80008031ffc8 x15: 0000000000000001
> x14: 1fffe0001ba5a290 x13: 0000000000000000 x12: 0000000000000003
> x11: 0000000000040000 x10: 0000000000000003 x9 : 0000000000000000
> x8 : 0000000002bcd3ae x7 : ffff80008aacbe30 x6 : 0000000000000000
> x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
> x2 : 0000000000000002 x1 : ffff80008aecd7e0 x0 : ffff80012545c000
> Call trace:
> __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
> arch_local_irq_enable arch/arm64/include/asm/irqflags.h:49 [inline]
> __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:386
> __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
> _raw_spin_unlock_bh+0x3c/0x4c kernel/locking/spinlock.c:210
> spin_unlock_bh include/linux/spinlock.h:396 [inline]
> batadv_tt_local_purge+0x264/0x2e8 net/batman-adv/translation-table.c:1356
> batadv_tt_local_resize_to_mtu+0xa0/0x154 net/batman-adv/translation-table.c:3956
> batadv_update_min_mtu+0x74/0xa4 net/batman-adv/hard-interface.c:651
> batadv_netlink_set_mesh+0x50c/0x1078 net/batman-adv/netlink.c:500
> genl_family_rcv_msg_doit net/netlink/genetlink.c:1113 [inline]
> genl_family_rcv_msg net/netlink/genetlink.c:1193 [inline]
> genl_rcv_msg+0x874/0xb6c net/netlink/genetlink.c:1208
> netlink_rcv_skb+0x214/0x3c4 net/netlink/af_netlink.c:2543
> genl_rcv+0x38/0x50 net/netlink/genetlink.c:1217
> netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
> netlink_unicast+0x65c/0x898 net/netlink/af_netlink.c:1367
> netlink_sendmsg+0x83c/0xb20 net/netlink/af_netlink.c:1908
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg net/socket.c:745 [inline]
> ____sys_sendmsg+0x56c/0x840 net/socket.c:2584
> ___sys_sendmsg net/socket.c:2638 [inline]
> __sys_sendmsg+0x26c/0x33c net/socket.c:2667
> __do_sys_sendmsg net/socket.c:2676 [inline]
> __se_sys_sendmsg net/socket.c:2674 [inline]
> __arm64_sys_sendmsg+0x80/0x94 net/socket.c:2674
> __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
> invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51
> el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136
> do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155
> el0_svc+0x54/0x158 arch/arm64/kernel/entry-common.c:678
> el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:696
> el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.8.0-rc2-syzkaller-g41bccc98fb79 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:51
> lr : default_idle_call+0xf8/0x128 kernel/sched/idle.c:103
> sp : ffff80008ebe7cd0
> x29: ffff80008ebe7cd0 x28: dfff800000000000 x27: 1ffff00011d7cfa8
> x26: ffff80008ec6d000 x25: 0000000000000000 x24: 0000000000000001
> x23: 1ffff00011d8da74 x22: ffff80008ec6d3a0 x21: 0000000000000000
> x20: ffff80008ec94e00 x19: ffff8000802cff08 x18: 1fffe000367ff796
> x17: ffff80008ec6d000 x16: ffff8000802cf7cc x15: 0000000000000001
> x14: 1fffe00036801310 x13: 0000000000000000 x12: 0000000000000003
> x11: 0000000000000001 x10: 0000000000000003 x9 : 0000000000000000
> x8 : 0000000000bf0413 x7 : ffff800080461668 x6 : 0000000000000000
> x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff80008ad5af48
> x2 : 0000000000000000 x1 : ffff80008aecd7e0 x0 : ffff80012543a000
> Call trace:
> __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
> arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:49
> cpuidle_idle_call kernel/sched/idle.c:170 [inline]
> do_idle+0x1f0/0x4e8 kernel/sched/idle.c:312
> cpu_startup_entry+0x5c/0x74 kernel/sched/idle.c:410
> rest_init+0x2dc/0x2f4 init/main.c:730
> start_kernel+0x0/0x4e8 init/main.c:827
> start_kernel+0x3e8/0x4e8 init/main.c:1072
> __primary_switched+0xb4/0xbc arch/arm64/kernel/head.S:523
>
>
> ---
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This patch [1] looks suspicious

I think batman-adv should reject too small MTU values.

[1]

commit d8e42a2b0addf238be8b3b37dcd9795a5c1be459
Author: Sven Eckelmann <sven@narfation.org>
Date: Wed Jul 19 10:01:15 2023 +0200

batman-adv: Don't increase MTU when set by user

If the user set an MTU value, it usually means that there are special
requirements for the MTU. But if an interface gots activated, the MTU was
always recalculated and then the user set value was overwritten.

The only reason why this user set value has to be overwritten, is when the
MTU has to be decreased because batman-adv is not able to transfer packets
with the user specified size.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Cc: stable@vger.kernel.org
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>