UnshareAfterEnterUserns() creates a pidfd via os.StartProcess() with
CLONE_PIDFD but fails to close the file descriptor in any code path,
resulting in a file descriptor leak for every container that uses user
namespace isolation.
The leak occurs because:
- The pidfd is created when PidFD field is set in SysProcAttr
- The original defer block only calls PidfdSendSignal() and
pidfdWaitid()
- No code path calls unix.Close(pidfd) to release the file descriptor
This causes one pidfd leak per container launch when user namespace
isolation is enabled (e.g., Kubernetes pods with hostUsers: false). In
production environments with high container churn, this can exhaust the
system's file descriptor limit.
Fix the leak by adding a defer statement immediately after process
creation that ensures unix.Close(pidfd) is always called, regardless of
which code path is taken. This guarantees cleanup even if the function
returns early due to errors or lack of pidfd support.
This follows the same cleanup pattern already established in
core/mount/mount_idmapped_utils_linux.go:getUsernsFD() which properly
closes its pidfd.
Closes: #12166
Signed-off-by: Jose Fernandez <josef@netflix.com>
[Move SupportsPidFD up to handle dupfd in Go 1.23.{0,1} and simplify backport]
Signed-off-by: Wei Fu <fuweid89@gmail.com>
Commit 8437c567d8 migrated the use of the
userns package to the github.com/moby/sys/user module.
After further discussion with maintainers, it was decided to move the
userns package to a separate module, as it has no direct relation with
"user" operations (other than having "user" in its name).
This patch migrates our code to use the new module.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
The userns package in libcontainer was integrated into the moby/sys/user
module at commit [3778ae603c706494fd1e2c2faf83b406e38d687d][1].
This patch deprecates the containerd fork of that package, and adds it as
an alias for the moby/sys/user/userns package.
[1]: https://github.com/opencontainers/runc/commit/3778ae603c706494fd1e2c2faf83b406e38d687d
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
We have quite a few pieces of code laying around containerd
that all loop and ignore eintr as they make syscalls directly
(or use a unix/syscall wrapper) because there's no stdlib
equivalent. This adds a small utility to pkg/sys that we can
use for all of these spots.
Signed-off-by: Danny Canter <danny@dcantah.dev>
Jose Fernandez