queue-6.18/bpf-limit-bpf-program-signature-size.patch

From 267e54468a68225a99ba740bf097f8102ed5804f Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Thu, 5 Feb 2026 07:38:07 +0100
Subject: bpf: Limit bpf program signature size

From: KP Singh <kpsingh@kernel.org>

[ Upstream commit ea1535e28bb3773fc0b3cbd1f3842b808016990c ]

Practical BPF signatures are significantly smaller than
KMALLOC_MAX_CACHE_SIZE

Allowing larger sizes opens the door for abuse by passing excessive
size values and forcing the kernel into expensive allocation paths (via
kmalloc_large or vmalloc).

Fixes: 349271568303 ("bpf: Implement signature verification for BPF programs")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260205063807.690823-1-kpsingh@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/syscall.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f39367765f0c4..2649e0472dfe0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2825,6 +2825,13 @@ static int bpf_prog_verify_signature(struct bpf_prog *prog, union bpf_attr *attr
 	void *sig;
 	int err = 0;
 
+	/*
+	 * Don't attempt to use kmalloc_large or vmalloc for signatures.
+	 * Practical signature for BPF program should be below this limit.
+	 */
+	if (attr->signature_size > KMALLOC_MAX_CACHE_SIZE)
+		return -EINVAL;
+
 	if (system_keyring_id_check(attr->keyring_id) == 0)
 		key = bpf_lookup_system_key(attr->keyring_id);
 	else
-- 
2.51.0