[PATCH] bpf: Ensure BPF programs testing skb context initialization

[Michal Switala]

This commit addresses an issue where a netdevice was found to be uninitialized.
To mitigate this case, the change ensures that BPF programs designed to test
skb context initialization thoroughly verify the availability of a fully
initialized context before execution.The root cause of a NULL ctx stems from
the initialization process in bpf_ctx_init(). This function returns NULL if
the user initializes the bpf_attr variables ctx_in and ctx_out with invalid
pointers or sets them to NULL. These variables are directly controlled by user
input, and if both are NULL, the context cannot be initialized, resulting in a
NULL ctx.

Reported-by: syzbot+cca39e6e84a367a7e6f6@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=cca39e6e84a367a7e6f6
Link: https://lore.kernel.org/all/000000000000b95d41061cbf302a@xxxxxxxxxx/
Signed-off-by: Michal Switala <michal.switala@xxxxxxxxxxxx>
---
 net/bpf/test_run.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 36ae54f57bf5..8b2efcee059f 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -970,7 +970,7 @@ static struct proto bpf_dummy_proto = {
 int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr)
 {
-	bool is_l2 = false, is_direct_pkt_access = false;
+	bool is_l2 = false, is_direct_pkt_access = false, ctx_needed = false;
 	struct net *net = current->nsproxy->net_ns;
 	struct net_device *dev = net->loopback_dev;
 	u32 size = kattr->test.data_size_in;
@@ -998,6 +998,34 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 		return PTR_ERR(ctx);
 	}
 
+	switch (prog->type) {
+	case BPF_PROG_TYPE_SOCKET_FILTER:
+	case BPF_PROG_TYPE_SCHED_CLS:
+	case BPF_PROG_TYPE_SCHED_ACT:
+	case BPF_PROG_TYPE_XDP:
+	case BPF_PROG_TYPE_CGROUP_SKB:
+	case BPF_PROG_TYPE_CGROUP_SOCK:
+	case BPF_PROG_TYPE_SOCK_OPS:
+	case BPF_PROG_TYPE_SK_SKB:
+	case BPF_PROG_TYPE_SK_MSG:
+	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
+	case BPF_PROG_TYPE_LWT_SEG6LOCAL:
+	case BPF_PROG_TYPE_SK_REUSEPORT:
+	case BPF_PROG_TYPE_NETFILTER:
+	case BPF_PROG_TYPE_LWT_IN:
+	case BPF_PROG_TYPE_LWT_OUT:
+	case BPF_PROG_TYPE_LWT_XMIT:
+		ctx_needed = true;
+		break;
+	default:
+		break;
+	}
+
+	if (!ctx && ctx_needed) {
+		kfree(data);
+		return -EINVAL;
+	}
+
 	switch (prog->type) {
 	case BPF_PROG_TYPE_SCHED_CLS:
 	case BPF_PROG_TYPE_SCHED_ACT:
-- 
2.43.0