CVE-2026-89766

In the Linux kernel, the following vulnerability has been resolved:

pidfd: hold exec_update_lock around namespace ioctl

The PIDFD_GET_*_NAMESPACE ioctls in pidfd_ioctl() perform a filesystem

credentials ptrace access check before handing out a namespace file

descriptor. The accompanying comment states that the code "mirrors nsfs

behavior", but, unlike the corresponding procfs paths, it does so without

holding the target task's exec_update_lock.

proc_ns_get_link() and proc_ns_readlink() both take exec_update_lock for

reading around the ptrace check and the namespace lookup, so that the

credentials used for the access decision match those of the task when its

namespace is read. Without it, a caller can pass the check against the

target's old credentials and then read the namespace after the target has

execve()'d a setuid binary and committed new credentials -- accessing

namespace information it should have been denied.

Hold exec_update_lock for reading around the ptrace check and the

namespace lookup so that pidfd truly mirrors nsfs behavior, as the comment

already claims. open_namespace() itself runs outside the lock: once a

namespace reference is obtained it carries its own refcount and is opened

with the caller's own credentials, so a concurrent execve() on the target

can no longer affect the outcome.