bpf, cgroup: Fix optlen WARN_ON_ONCE toctou

[ Upstream commit bb8b81e396f7afbe7c50d789e2107512274d2a35 ]

A toctou issue in `__cgroup_bpf_run_filter_getsockopt` can trigger a
WARN_ON_ONCE in a check of `copy_from_user`.

`*optlen` is checked to be non-negative in the individual getsockopt
functions beforehand. Changing `*optlen` in a race to a negative value
will result in a `copy_from_user(ctx.optval, optval, ctx.optlen)` with
`ctx.optlen` being a negative integer.

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/20210122164232.61770-1-loris.reiff@liblor.ch
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5a8b4dfdb1419b473d34bcedbb759d95d5519da2..5b2413eb79db4a27b71c9ef35608609813d4cf2a 100644 (file)
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1109,6 +1109,11 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
                        goto out;
                }
 
+               if (ctx.optlen < 0) {
+                       ret = -EFAULT;
+                       goto out;
+               }
+
                if (copy_from_user(ctx.optval, optval,
                                   min(ctx.optlen, max_optlen)) != 0) {
                        ret = -EFAULT;