Re: [PATCH net] net: add softirq safety to netdev_rename_lock

[Kuniyuki Iwashima <kuniyu@amazon.com>]

Date: Thu, 20 Jun 2024 13:31:19 +0000
From: Eric Dumazet <edumazet@google.com>
> syzbot reported a lockdep violation involving bridge driver [1]
> 
> Make sure netdev_rename_lock is softirq safe to fix this issue.
> 
> [1]
> WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
> 6.10.0-rc2-syzkaller-00249-gbe27b8965297 #0 Not tainted
>    -----------------------------------------------------
> syz-executor.2/9449 [HC0[0]:SC0[2]:HE0:SE0] is trying to acquire:
>  ffffffff8f5de668 (netdev_rename_lock.seqcount){+.+.}-{0:0}, at: rtnl_fill_ifinfo+0x38e/0x2270 net/core/rtnetlink.c:1839
> 
> and this task is already holding:
>  ffff888060c64cb8 (&br->lock){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
>  ffff888060c64cb8 (&br->lock){+.-.}-{2:2}, at: br_port_slave_changelink+0x3d/0x150 net/bridge/br_netlink.c:1212
> which would create a new lock dependency:
>  (&br->lock){+.-.}-{2:2} -> (netdev_rename_lock.seqcount){+.+.}-{0:0}
> 
> but this new dependency connects a SOFTIRQ-irq-safe lock:
>  (&br->lock){+.-.}-{2:2}
[...]
> Fixes: 0840556e5a3a ("net: Protect dev->name by seqlock.")
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thanks!