[PATCH 6.1 374/473] um: Add winch to winch_handlers before registering winch IRQ

Greg Kroah-Hartman
2024-06-06T14:18:22Z

From: Roberto Sassu <roberto.sassu@huawei.com>

[ Upstream commit a0fbbd36c156b9f7b2276871d499c9943dfe5101 ]

Registering a winch IRQ is racy, an interrupt may occur before the winch is
added to the winch_handlers list.

If that happens, register_winch_irq() adds to that list a winch that is
scheduled to be (or has already been) freed, causing a panic later in
winch_cleanup().

Avoid the race by adding the winch to the winch_handlers list before
registering the IRQ, and rolling back if um_request_irq() fails.

Fixes: 42a359e31a0e ("uml: SIGIO support cleanup")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/um/drivers/line.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 02b0befd67632..95ad6b190d1d1 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -673,24 +673,26 @@ void register_winch_irq(int fd, int tty_fd, int pid, struct tty_port *port,
goto cleanup;
}

- *winch = ((struct winch) { .list = LIST_HEAD_INIT(winch->list),
- .fd = fd,
+ *winch = ((struct winch) { .fd = fd,
.tty_fd = tty_fd,
.pid = pid,
.port = port,
.stack = stack });

+ spin_lock(&winch_handler_lock);
+ list_add(&winch->list, &winch_handlers);
+ spin_unlock(&winch_handler_lock);
+
if (um_request_irq(WINCH_IRQ, fd, IRQ_READ, winch_interrupt,
IRQF_SHARED, "winch", winch) < 0) {
printk(KERN_ERR "register_winch_irq - failed to register "
"IRQ\n");
+ spin_lock(&winch_handler_lock);
+ list_del(&winch->list);
+ spin_unlock(&winch_handler_lock);
goto out_free;
}

- spin_lock(&winch_handler_lock);
- list_add(&winch->list, &winch_handlers);
- spin_unlock(&winch_handler_lock);
-
return;

out_free:
--
2.43.0