From 4f11ada10d0ad3fd53e2bd67806351de63a4f9c3 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Tue, 24 Jan 2023 16:41:18 +0100 Subject: ovl: fail on invalid uid/gid mapping at copy up 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: # v5.11 Signed-off-by: Miklos Szeredi Reviewed-by: Christian Brauner Reviewed-by: Seth Forshee --- fs/overlayfs/copy_up.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs') 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) { -- cgit v1.2.3