[PATCH 03/11] vfs: Fix race condition on get_userns_fd()

[Rodrigo Campos <rodrigo@sdfg.com.ar>]

Talking with Christian Brauner about a different problem, he mentioned
that technically this race condition exists and we should fix it.

The race is that when we clone, we call a function that just returns
while at the same time we try to get the userns via /proc/pid/ns/user.
The thing is that, while the pid needs to be reaped, Christian said that
the userns file cease to exist as soon as the program finishes.

So, let's make the function never return, so we always can get the
userns. We are already sending a SIGKILL to this pid, so nothing else
remaining to not leak the process.

Signed-off-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
---
 src/vfs/utils.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git src/vfs/utils.c src/vfs/utils.c
index ea7536c1..67779e83 100644
--- src/vfs/utils.c
+++ src/vfs/utils.c
@@ -58,9 +58,10 @@ pid_t do_clone(int (*fn)(void *), void *arg, int flags)
 #endif
 }
 
-static int get_userns_fd_cb(void *data)
+__attribute__((noreturn)) static int get_userns_fd_cb(void *data)
 {
-	return 0;
+	for (;;)
+		pause();
 }
 
 int wait_for_pid(pid_t pid)
-- 
2.39.2