tree 6d5af52753b913796881503e2814593f7b979e73
parent 978ebbf3170252b28b4624d660f8b8e246ce133e
author Miklos Szeredi <mszeredi@redhat.com> 1674574878 +0100
committer Nobel Barakat <nobelbarakat@google.com> 1680111776 +0000

ovl: fail on invalid uid/gid mapping at copy up

commit 4f11ada10d0ad3fd53e2bd67806351de63a4f9c3 upstream.

If st_uid/st_gid doesn't have a mapping in the mounter's user_ns, then
copy-up should fail, just like it would fail if the mounter task was doing
the copy using "cp -a".

There's a corner case where the "cp -a" would succeed but copy up fail: if
there's a mapping of the invalid uid/gid (65534 by default) in the user
namespace.  This is because stat(2) will return this value if the mapping
doesn't exist in the current user_ns and "cp -a" will in turn be able to
create a file with this uid/gid.

This behavior would be inconsistent with POSIX ACL's, which return -1 for
invalid uid/gid which result in a failed copy.

For consistency and simplicity fail the copy of the st_uid/st_gid are
invalid.

Fixes: 459c7c565ac3 ("ovl: unprivieged mounts")
Cc: <stable@vger.kernel.org> # v5.11
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Seth Forshee <sforshee@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

BUG=b/275534143
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2023-0386 in overlayfs.

cos-patch: security-high
Change-Id: I874cda187136a876d7158d412b933769dde6644b
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/45687
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Vaibhav Rustagi <vaibhavrustagi@google.com>