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From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 24 Jan 2023 16:41:18 +0100
Subject: ovl: fail on invalid uid/gid mapping at copy up
Origin: https://git.kernel.org/linus/4f11ada10d0ad3fd53e2bd67806351de63a4f9c3
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2023-0386
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>
---
fs/overlayfs/copy_up.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 140f2742074d..c14e90764e35 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -1011,6 +1011,10 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
if (err)
return err;
+ if (!kuid_has_mapping(current_user_ns(), ctx.stat.uid) ||
+ !kgid_has_mapping(current_user_ns(), ctx.stat.gid))
+ return -EOVERFLOW;
+
ctx.metacopy = ovl_need_meta_copy_up(dentry, ctx.stat.mode, flags);
if (parent) {
--
2.40.1
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