From: Loris Reiff <loris.reiff@liblor.ch>
Date: Fri, 22 Jan 2021 17:42:31 +0100
Subject: bpf, cgroup: Fix optlen WARN_ON_ONCE toctou
Patch-mainline: Queued in subsystem maintainer repository
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Git-commit: bb8b81e396f7afbe7c50d789e2107512274d2a35
References: bsc#1155518

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
Acked-by: Gary Lin <glin@suse.com>
---
 kernel/bpf/cgroup.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1109,6 +1109,11 @@ int __cgroup_bpf_run_filter_getsockopt(s
 			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;