[PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

[PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

[Chengfeng Ye]

As &net->sctp.addr_wq_lock is also acquired by the timer
sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
at sctp_auto_asconf_init() seems should disable irq since it is called
from sctp_accept() under process context.

Possible deadlock scenario:
sctp_accept()
    -> sctp_sock_migrate()
    -> sctp_auto_asconf_init()
    -> spin_lock(&net->sctp.addr_wq_lock)
        <timer interrupt>
        -> sctp_addr_wq_timeout_handler()
        -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)

This flaw was found using an experimental static analysis tool we are
developing for irq-related deadlock.

The tentative patch fix the potential deadlock by spin_lock_bh().

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 net/sctp/socket.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index cda8c2874691..b2c7d17ff848 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -364,9 +364,9 @@ static void sctp_auto_asconf_init(struct sctp_sock *sp)
 	struct net *net = sock_net(&sp->inet.sk);
 
 	if (net->sctp.default_auto_asconf) {
-		spin_lock(&net->sctp.addr_wq_lock);
+		spin_lock_bh(&net->sctp.addr_wq_lock);
 		list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
-		spin_unlock(&net->sctp.addr_wq_lock);
+		spin_unlock_bh(&net->sctp.addr_wq_lock);
 		sp->do_auto_asconf = 1;
 	}
 }
-- 
2.17.1

Re: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

[Xin Long]

On Tue, Jun 27, 2023 at 8:04 AM Chengfeng Ye <dg573847474@gmail.com> wrote:
>
> As &net->sctp.addr_wq_lock is also acquired by the timer
> sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
> at sctp_auto_asconf_init() seems should disable irq since it is called
> from sctp_accept() under process context.
>
> Possible deadlock scenario:
> sctp_accept()
>     -> sctp_sock_migrate()
>     -> sctp_auto_asconf_init()
>     -> spin_lock(&net->sctp.addr_wq_lock)
>         <timer interrupt>
>         -> sctp_addr_wq_timeout_handler()
>         -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)
>
> This flaw was found using an experimental static analysis tool we are
> developing for irq-related deadlock.
>
> The tentative patch fix the potential deadlock by spin_lock_bh().
>
> Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
> ---
>  net/sctp/socket.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index cda8c2874691..b2c7d17ff848 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -364,9 +364,9 @@ static void sctp_auto_asconf_init(struct sctp_sock *sp)
>         struct net *net = sock_net(&sp->inet.sk);
>
>         if (net->sctp.default_auto_asconf) {
> -               spin_lock(&net->sctp.addr_wq_lock);
> +               spin_lock_bh(&net->sctp.addr_wq_lock);
>                 list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
> -               spin_unlock(&net->sctp.addr_wq_lock);
> +               spin_unlock_bh(&net->sctp.addr_wq_lock);
>                 sp->do_auto_asconf = 1;
>         }
>  }
> --
> 2.17.1
>
Fixes: 34e5b0118685 ("sctp: delay auto_asconf init until binding the
first addr")
Acked-by: Xin Long <lucien.xin@gmail.com>

Thanks.

Re: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

[Paolo Abeni]

On Tue, 2023-06-27 at 12:03 +0000, Chengfeng Ye wrote:
> As &net->sctp.addr_wq_lock is also acquired by the timer
> sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
> at sctp_auto_asconf_init() seems should disable irq since it is called
> from sctp_accept() under process context.
> 
> Possible deadlock scenario:
> sctp_accept()
>     -> sctp_sock_migrate()
>     -> sctp_auto_asconf_init()
>     -> spin_lock(&net->sctp.addr_wq_lock)
>         <timer interrupt>
>         -> sctp_addr_wq_timeout_handler()
>         -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)
> 
> This flaw was found using an experimental static analysis tool we are
> developing for irq-related deadlock.
> 
> The tentative patch fix the potential deadlock by spin_lock_bh().

Patch LGTM.

Please note that the above suggests a possible net-next follow-
up/cleanup, replacing the spin_lock_bh() in
sctp_addr_wq_timeout_handler() with a simple/faster spin_lock() - since
sctp_addr_wq_timeout_handler() runs with BH disabled. Anyhow net-next
is closed now, it will have to wait a bit ;)

Cheers,

Paolo

Re: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Tue, 27 Jun 2023 12:03:40 +0000 you wrote:
> As &net->sctp.addr_wq_lock is also acquired by the timer
> sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
> at sctp_auto_asconf_init() seems should disable irq since it is called
> from sctp_accept() under process context.
> 
> Possible deadlock scenario:
> sctp_accept()
>     -> sctp_sock_migrate()
>     -> sctp_auto_asconf_init()
>     -> spin_lock(&net->sctp.addr_wq_lock)
>         <timer interrupt>
>         -> sctp_addr_wq_timeout_handler()
>         -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)
> 
> [...]

Here is the summary with links:
  - sctp: fix potential deadlock on &net->sctp.addr_wq_lock
    https://git.kernel.org/netdev/net/c/6feb37b3b06e

You are awesome, thank you!
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