6.12-stable review patch. If anyone has any objections, please let me know.
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From: Sven Stegemann sven@stegemann.de
[ Upstream commit 52565a935213cd6a8662ddb8efe5b4219343a25d ]
syzbot found a race condition when kcm_unattach(psock) and kcm_release(kcm) are executed at the same time.
kcm_unattach() is missing a check of the flag kcm->tx_stopped before calling queue_work().
If the kcm has a reserved psock, kcm_unattach() might get executed between cancel_work_sync() and unreserve_psock() in kcm_release(), requeuing kcm->tx_work right before kcm gets freed in kcm_done().
Remove kcm->tx_stopped and replace it by the less error-prone disable_work_sync().
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Reported-by: syzbot+e62c9db591c30e174662@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=e62c9db591c30e174662 Reported-by: syzbot+d199b52665b6c3069b94@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d199b52665b6c3069b94 Reported-by: syzbot+be6b1fdfeae512726b4e@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=be6b1fdfeae512726b4e Signed-off-by: Sven Stegemann sven@stegemann.de Link: https://patch.msgid.link/20250812191810.27777-1-sven@stegemann.de Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/kcm.h | 1 - net/kcm/kcmsock.c | 10 ++-------- 2 files changed, 2 insertions(+), 9 deletions(-)
diff --git a/include/net/kcm.h b/include/net/kcm.h index 441e993be634..d9c35e71ecea 100644 --- a/include/net/kcm.h +++ b/include/net/kcm.h @@ -71,7 +71,6 @@ struct kcm_sock { struct list_head wait_psock_list; struct sk_buff *seq_skb; struct mutex tx_mutex; - u32 tx_stopped : 1;
/* Don't use bit fields here, these are set under different locks */ bool tx_wait; diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index d4118c796290..1d37b26ea2ef 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -429,7 +429,7 @@ static void psock_write_space(struct sock *sk)
/* Check if the socket is reserved so someone is waiting for sending. */ kcm = psock->tx_kcm; - if (kcm && !unlikely(kcm->tx_stopped)) + if (kcm) queue_work(kcm_wq, &kcm->tx_work);
spin_unlock_bh(&mux->lock); @@ -1696,12 +1696,6 @@ static int kcm_release(struct socket *sock) */ __skb_queue_purge(&sk->sk_write_queue);
- /* Set tx_stopped. This is checked when psock is bound to a kcm and we - * get a writespace callback. This prevents further work being queued - * from the callback (unbinding the psock occurs after canceling work. - */ - kcm->tx_stopped = 1; - release_sock(sk);
spin_lock_bh(&mux->lock); @@ -1717,7 +1711,7 @@ static int kcm_release(struct socket *sock) /* Cancel work. After this point there should be no outside references * to the kcm socket. */ - cancel_work_sync(&kcm->tx_work); + disable_work_sync(&kcm->tx_work);
lock_sock(sk); psock = kcm->tx_psock;