The code to copy file descriptors was duplicated in pidfd_getfd. Rather than continue to duplicate it, this hoists the code out of kernel/pid.c and uses the newly added file_receive helper.

Earlier, when this was implemented there was some back-and-forth about how the semantics should work around copying around file descriptors [1], and it was decided that the default behaviour should be to not modify cgroup data. As a matter of least surprise, this approach follows the default semantics as presented by SCM_RIGHTS.

In the future, a flag can be added to avoid manipulating the cgroup data on copy.

[1]: https://lore.kernel.org/lkml/20200107175927.4558-1-sargun@sargun.me/

Signed-off-by: Sargun Dhillon sargun@sargun.me Suggested-by: Kees Cook keescook@chromium.org Cc: Al Viro viro@zeniv.linux.org.uk Cc: Christian Brauner christian.brauner@ubuntu.com Cc: Daniel Wagner daniel.wagner@bmw-carit.de Cc: David S. Miller davem@davemloft.net Cc: Jann Horn jannh@google.com Cc: John Fastabend john.r.fastabend@intel.com Cc: Tejun Heo tj@kernel.org Cc: Tycho Andersen tycho@tycho.ws Cc: stable@vger.kernel.org Cc: cgroups@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- kernel/pid.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c index c835b844aca7..1642cf940aa1 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -606,7 +606,7 @@ static int pidfd_getfd(struct pid *pid, int fd) { struct task_struct *task; struct file *file; - int ret; + int ret, err;

task = get_pid_task(pid, PIDTYPE_PID); if (!task) @@ -617,18 +617,16 @@ static int pidfd_getfd(struct pid *pid, int fd) if (IS_ERR(file)) return PTR_ERR(file);

- ret = security_file_receive(file); - if (ret) { - fput(file); - return ret; - } - ret = get_unused_fd_flags(O_CLOEXEC); - if (ret < 0) - fput(file); - else - fd_install(ret, file); + if (ret >= 0) { + err = file_receive(ret, file); + if (err) { + put_unused_fd(ret); + ret = err; + } + }

+ fput(file); return ret; }