[SRU Groovy 2/2] bpf, cgroup: Fix problematic bounds check

[Thadeu Lima de Souza Cascardo]

From: Loris Reiff <loris.reiff at liblor.ch>

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 at liblor.ch>
Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf at google.com>
Link: https://lore.kernel.org/bpf/20210122164232.61770-2-loris.reiff@liblor.ch
(cherry picked from commit f4a2da755a7e1f5d845c52aee71336cee289935a)
CVE-2021-20194
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 kernel/bpf/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 7bae3686603e..c1fd5ca6fab6 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1439,7 +1439,7 @@ 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;
 	}
-- 
2.27.0