On 10/9/22 11:42 AM, Yosry Ahmed wrote:
On Sun, Oct 9, 2022 at 6:10 AM Christian A. Ehrhardt <lk@xxxxxxx> wrote:
Since commit f3a2aebdd6, Version 1 cgroups no longer cause an
error when used with CLONE_INTO_CGROUP. However, the permission
checks performed during clone assume a Version 2 cgroup.
Restore the error check for V1 cgroups in the clone() path.
Reported-by: syzbot+534ee3d24c37c411f37f@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/lkml/000000000000385cbf05ea3f1862@xxxxxxxxxx/
Fixes: f3a2aebdd6 ("cgroup: enable cgroup_get_from_file() on cgroup1")
Thanks for fixing this, and sorry if this caused a mess.
cgroup_get_from_file() independently seemed like it can support
cgroup1, I didn't realize that some of the callers depend on the fact
that it only supports cgroup2.
+Andrii Nakryiko +Alexei Starovoitov +Martin KaFai Lau +bpf
I wonder if BPF users have this dependency. Does cgroup_bpf_attach()
also depend on cgroup_get_from_fd() (which calls
cgroup_get_from_file()) eliminating v1 cgroups?
Yes, cgroup_bpf_{prog,link}_attach() depends on cgroup_get_from_fd() only
returning v2 cgroup. Thus, it needs a fix to get back this filtering after
commit f3a2aebdd6.
It seems like cgroup storages (and some other places) use cgroup ids.
Collisions can happen in cgroup1 ids so I am assuming we want to add a
check there as well. Perhaps in cgroup_bpf_attach() ?
From a quick look, cgroup storage should be fine. The insertion (where the
cgrp is required for the key purpose) has already passed the attach filtering.
Where 'other places' might have problem with the cgroup id?
I can send a patch for this if that's the case.
Signed-off-by: Christian A. Ehrhardt <lk@xxxxxxx>
---
kernel/cgroup/cgroup.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b6e3110b3ea7..f7fc3afa88c1 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6244,6 +6244,11 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
goto err;
}
+ if (!cgroup_on_dfl(dst_cgrp)) {
+ ret = -EBADF;
+ goto err;
+ }
+
if (cgroup_is_dead(dst_cgrp)) {
ret = -ENODEV;
goto err;
--
2.34.1
