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authorAndrei Vagin <avagin@gmail.com>2022-06-12 23:07:22 -0700
committerKees Cook <keescook@chromium.org>2022-06-15 07:58:04 -0700
commit133e2d3e81de5d9706cab2dd1d52d231c27382e5 (patch)
tree04ff6fdda3b663c9069512108da2b73483134af8 /kernel/fork.c
parentb13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3 (diff)
fs/exec: allow to unshare a time namespace on vfork+exec
Right now, a new process can't be forked in another time namespace if it shares mm with its parent. It is prohibited, because each time namespace has its own vvar page that is mapped into a process address space. When a process calls exec, it gets a new mm and so it could be "legal" to switch time namespace in that case. This was not implemented and now if we want to do this, we need to add another clone flag to not break backward compatibility. We don't have any user requests to switch times on exec except the vfork+exec combination, so there is no reason to add a new clone flag. As for vfork+exec, this should be safe to allow switching timens with the current clone flag. Right now, vfork (CLONE_VFORK | CLONE_VM) fails if a child is forked into another time namespace. With this change, vfork creates a new process in parent's timens, and the following exec does the actual switch to the target time namespace. Suggested-by: Florian Weimer <fweimer@redhat.com> Signed-off-by: Andrei Vagin <avagin@gmail.com> Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220613060723.197407-1-avagin@gmail.com
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 9d44f2d46c69..9174146f6812 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2033,8 +2033,11 @@ static __latent_entropy struct task_struct *copy_process(
/*
* If the new process will be in a different time namespace
* do not allow it to share VM or a thread group with the forking task.
+ *
+ * On vfork, the child process enters the target time namespace only
+ * after exec.
*/
- if (clone_flags & (CLONE_THREAD | CLONE_VM)) {
+ if ((clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM) {
if (nsp->time_ns != nsp->time_ns_for_children)
return ERR_PTR(-EINVAL);
}