From: Tycho Andersen <tandersen@xxxxxxxxxxx> We can get EBADF from __pidfd_fget() if a task is currently exiting, which might be confusing. Let's check PF_EXITING, and just report ESRCH if so. I chose PF_EXITING, because it is set in exit_signals(), which is called before exit_files(). Since ->exit_status is mostly set after exit_files() in exit_notify(), using that still leaves a window open for the race. Signed-off-by: Tycho Andersen <tandersen@xxxxxxxxxxx> --- kernel/pid.c | 2 +- .../selftests/pidfd/pidfd_getfd_test.c | 31 ++++++++++++++++++- 2 files changed, 31 insertions(+), 2 deletions(-) diff --git a/kernel/pid.c b/kernel/pid.c index de0bf2f8d18b..db8731f0ee45 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -688,7 +688,7 @@ static int pidfd_getfd(struct pid *pid, int fd) int ret; task = get_pid_task(pid, PIDTYPE_PID); - if (!task) + if (!task || task->flags & PF_EXITING) return -ESRCH; file = __pidfd_fget(task, fd); diff --git a/tools/testing/selftests/pidfd/pidfd_getfd_test.c b/tools/testing/selftests/pidfd/pidfd_getfd_test.c index 0930e2411dfb..cd51d547b751 100644 --- a/tools/testing/selftests/pidfd/pidfd_getfd_test.c +++ b/tools/testing/selftests/pidfd/pidfd_getfd_test.c @@ -5,6 +5,7 @@ #include <fcntl.h> #include <limits.h> #include <linux/types.h> +#include <poll.h> #include <sched.h> #include <signal.h> #include <stdio.h> @@ -129,6 +130,7 @@ FIXTURE(child) * When it is closed, the child will exit. */ int sk; + bool ignore_child_result; }; FIXTURE_SETUP(child) @@ -165,10 +167,14 @@ FIXTURE_SETUP(child) FIXTURE_TEARDOWN(child) { + int ret; + EXPECT_EQ(0, close(self->pidfd)); EXPECT_EQ(0, close(self->sk)); - EXPECT_EQ(0, wait_for_pid(self->pid)); + ret = wait_for_pid(self->pid); + if (!self->ignore_child_result) + EXPECT_EQ(0, ret); } TEST_F(child, disable_ptrace) @@ -235,6 +241,29 @@ TEST(flags_set) EXPECT_EQ(errno, EINVAL); } +TEST_F(child, no_strange_EBADF) +{ + struct pollfd fds; + + self->ignore_child_result = true; + + fds.fd = self->pidfd; + fds.events = POLLIN; + + ASSERT_EQ(kill(self->pid, SIGKILL), 0); + ASSERT_EQ(poll(&fds, 1, 5000), 1); + + /* + * It used to be that pidfd_getfd() could race with the exiting thread + * between exit_files() and release_task(), and get a non-null task + * with a NULL files struct, and you'd get EBADF, which was slightly + * confusing. + */ + errno = 0; + EXPECT_EQ(sys_pidfd_getfd(self->pidfd, self->remote_fd, 0), -1); + EXPECT_EQ(errno, ESRCH); +} + #if __NR_pidfd_getfd == -1 int main(void) { base-commit: 082d11c164aef02e51bcd9c7cbf1554a8e42d9b5 -- 2.34.1