[PATCH 5.4 253/411] um: chan_user: Fix winch_tramp() return value

Greg Kroah-Hartman
2022-06-13T11:34:57Z

From: Johannes Berg <johannes.berg@intel.com>

commit 57ae0b67b747031bc41fb44643aa5344ab58607e upstream.

The previous fix here was only partially correct, it did
result in returning a proper error value in case of error,
but it also clobbered the pid that we need to return from
this function (not just zero for success).

As a result, it returned 0 here, but later this is treated
as a pid and used to kill the process, but since it's now
0 we kill(0, SIGKILL), which makes UML kill itself rather
than just the helper thread.

Fix that and make it more obvious by using a separate
variable for the pid.

Fixes: ccf1236ecac4 ("um: fix error return code in winch_tramp()")
Reported-and-tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/um/drivers/chan_user.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -220,7 +220,7 @@ static int winch_tramp(int fd, struct tt
unsigned long *stack_out)
{
struct winch_data data;
- int fds[2], n, err;
+ int fds[2], n, err, pid;
char c;

err = os_pipe(fds, 1, 1);
@@ -238,8 +238,9 @@ static int winch_tramp(int fd, struct tt
* problem with /dev/net/tun, which if held open by this
* thread, prevents the TUN/TAP device from being reused.
*/
- err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
- if (err < 0) {
+ pid = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
+ if (pid < 0) {
+ err = pid;
printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
-err);
goto out_close;
@@ -263,7 +264,7 @@ static int winch_tramp(int fd, struct tt
goto out_close;
}

- return err;
+ return pid;

out_close:
close(fds[1]);