[PATCH stable 6.12 2/9] um: Set parent death signal for winch thread/process

[Florian Fainelli]

From: Benjamin Berg <benjamin.berg@xxxxxxxxx>

commit fdb2ecd35d327a1fc6bba69b97f85b494e1f4b6b upstream

The winch "thread" is really a separate process. Using prctl to set
PR_SET_PDEATHSIG ensures that this separate thread will be killed if the
UML kernel itself dies unexpectedly and does not perform proper cleanup.

Signed-off-by: Benjamin Berg <benjamin.berg@xxxxxxxxx>
Link: https://patch.msgid.link/20240919124511.282088-5-benjamin@xxxxxxxxxxxxxxxx
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
---
 arch/um/drivers/chan_user.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index a66e556012c4..1434114b2f34 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -10,6 +10,7 @@
 #include <signal.h>
 #include <termios.h>
 #include <sys/ioctl.h>
+#include <sys/prctl.h>
 #include "chan_user.h"
 #include <os.h>
 #include <um_malloc.h>
@@ -161,6 +162,8 @@ static __noreturn int winch_thread(void *arg)
 	int count;
 	char c = 1;
 
+	prctl(PR_SET_PDEATHSIG, SIGKILL);
+
 	pty_fd = data->pty_fd;
 	pipe_fd = data->pipe_fd;
 	count = write(pipe_fd, &c, sizeof(c));
-- 
2.34.1