RE: [PATCH bpf] bpf, sockmap: Prevent lock inversion deadlock in map delete elem

[John Fastabend <john.fastabend@gmail.com>]

Jakub Sitnicki wrote:
> syzkaller started using corpuses where a BPF tracing program deletes
> elements from a sockmap/sockhash map. Because BPF tracing programs can be
> invoked from any interrupt context, locks taken during a map_delete_elem
> operation must be hardirq-safe. Otherwise a deadlock due to lock inversion
> is possible, as reported by lockdep:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&htab->buckets[i].lock);
>                                local_irq_disable();
>                                lock(&host->lock);
>                                lock(&htab->buckets[i].lock);
>   <Interrupt>
>     lock(&host->lock);
> 
> Locks in sockmap are hardirq-unsafe by design. We expects elements to be
> deleted from sockmap/sockhash only in task (normal) context with interrupts
> enabled, or in softirq context.
> 
> Detect when map_delete_elem operation is invoked from a context which is
> _not_ hardirq-unsafe, that is interrupts are disabled, and bail out with an
> error.
> 
> Note that map updates are not affected by this issue. BPF verifier does not
> allow updating sockmap/sockhash from a BPF tracing program today.
> 
> Reported-by: xingwei lee <xrivendell7@gmail.com>
> Reported-by: yue sun <samsun1006219@gmail.com>
> Reported-by: syzbot+bc922f476bd65abbd466@syzkaller.appspotmail.com
> Reported-and-tested-by: syzbot+d4066896495db380182e@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=d4066896495db380182e
> Closes: https://syzkaller.appspot.com/bug?extid=bc922f476bd65abbd466
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Edward Adam Davis <eadavis@qq.com>
> Cc: Shung-Hsi Yu <shung-hsi.yu@suse.com>
> ---
>  net/core/sock_map.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Agree.

Acked-by: John Fastabend <john.fastabend@gmail.com>