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| author | Andrei Vagin <avagin@gmail.com> | 2022-09-20 17:31:19 -0700 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2022-10-25 15:15:52 -0700 |
| commit | 2b5f9dad32ed19e8db3b0f10a84aa824a219803b (patch) | |
| tree | 58e00059792fc68cf5e76067814f6b92c1ab20ed /kernel/nsproxy.c | |
| parent | 594d2a14f2168c09b13b114c3d457aa939403e52 (diff) | |
| download | lwn-2b5f9dad32ed19e8db3b0f10a84aa824a219803b.tar.gz lwn-2b5f9dad32ed19e8db3b0f10a84aa824a219803b.zip | |
fs/exec: switch timens when a task gets a new mm
Changing a time namespace requires remapping a vvar page, so we don't want
to allow doing that if any other tasks can use the same mm.
Currently, we install a time namespace when a task is created with a new
vm. exec() is another case when a task gets a new mm and so it can switch
a time namespace safely, but it isn't handled now.
One more issue of the current interface is that clone() with CLONE_VM isn't
allowed if the current task has unshared a time namespace
(timens_for_children doesn't match the current timens).
Both these issues make some inconvenience for users. For example, Alexey
and Florian reported that posix_spawn() uses vfork+exec and this pattern
doesn't work with time namespaces due to the both described issues.
LXC needed to workaround the exec() issue by calling setns.
In the commit 133e2d3e81de5 ("fs/exec: allow to unshare a time namespace on
vfork+exec"), we tried to fix these issues with minimal impact on UAPI. But
it adds extra complexity and some undesirable side effects. Eric suggested
fixing the issues properly because here are all the reasons to suppose that
there are no users that depend on the old behavior.
Cc: Alexey Izbyshev <izbyshev@ispras.ru>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Suggested-by: "Eric W. Biederman" <ebiederm@xmission.com>
Origin-author: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220921003120.209637-1-avagin@google.com
Diffstat (limited to 'kernel/nsproxy.c')
| -rw-r--r-- | kernel/nsproxy.c | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c index eec72ca962e2..a487ff24129b 100644 --- a/kernel/nsproxy.c +++ b/kernel/nsproxy.c @@ -157,7 +157,8 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk) if (likely(!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET | CLONE_NEWCGROUP | CLONE_NEWTIME)))) { - if (likely(old_ns->time_ns_for_children == old_ns->time_ns)) { + if ((flags & CLONE_VM) || + likely(old_ns->time_ns_for_children == old_ns->time_ns)) { get_nsproxy(old_ns); return 0; } @@ -179,7 +180,8 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk) if (IS_ERR(new_ns)) return PTR_ERR(new_ns); - timens_on_fork(new_ns, tsk); + if ((flags & CLONE_VM) == 0) + timens_on_fork(new_ns, tsk); tsk->nsproxy = new_ns; return 0; @@ -254,6 +256,23 @@ void exit_task_namespaces(struct task_struct *p) switch_task_namespaces(p, NULL); } +int exec_task_namespaces(void) +{ + struct task_struct *tsk = current; + struct nsproxy *new; + + if (tsk->nsproxy->time_ns_for_children == tsk->nsproxy->time_ns) + return 0; + + new = create_new_namespaces(0, tsk, current_user_ns(), tsk->fs); + if (IS_ERR(new)) + return PTR_ERR(new); + + timens_on_fork(new, tsk); + switch_task_namespaces(tsk, new); + return 0; +} + static int check_setns_flags(unsigned long flags) { if (!flags || (flags & ~(CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | |