bpf, cgroup: Fix problematic bounds check

Since ctx.optlen is signed, a larger value than max_value could be
passed, as it is later on used as unsigned, which causes a WARN_ON_ONCE
in the copy_to_user.

Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
Signed-off-by: Loris Reiff <loris.reiff@liblor.ch>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20210122164232.61770-2-loris.reiff@liblor.ch

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 6ec8f02..6aa9e10 100644 (file)
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1464,7 +1464,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
                goto out;
        }
 
-       if (ctx.optlen > max_optlen) {
+       if (ctx.optlen > max_optlen || ctx.optlen < 0) {
                ret = -EFAULT;
                goto out;
        }