netdev - [PATCH bpf] bpf: fix bpf_skb_load_bytes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:   Sat, 28 Jul 2018 21:04:19 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     netdev@...r.kernel.org
Cc:     kafai@...com, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf] bpf: fix bpf_skb_load_bytes_relative pkt length check

The len > skb_headlen(skb) cannot be used as a maximum upper bound
for the packet length since it does not have any relation to the full
linear packet length when filtering is used from upper layers (e.g.
in case of reuseport BPF programs) as by then skb->data, skb->len
already got mangled through __skb_pull() and others.

Fixes: 4e1ec56cdc59 ("bpf: add skb_load_bytes_relative helper")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Martin KaFai Lau <kafai@...com>
---
 net/core/filter.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 06da770..9dfd145 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1712,24 +1712,26 @@ static const struct bpf_func_proto bpf_skb_load_bytes_proto = {
 BPF_CALL_5(bpf_skb_load_bytes_relative, const struct sk_buff *, skb,
 	   u32, offset, void *, to, u32, len, u32, start_header)
 {
+	u8 *end = skb_tail_pointer(skb);
+	u8 *net = skb_network_header(skb);
+	u8 *mac = skb_mac_header(skb);
 	u8 *ptr;
 
-	if (unlikely(offset > 0xffff || len > skb_headlen(skb)))
+	if (unlikely(offset > 0xffff || len > (end - mac)))
 		goto err_clear;
 
 	switch (start_header) {
 	case BPF_HDR_START_MAC:
-		ptr = skb_mac_header(skb) + offset;
+		ptr = mac + offset;
 		break;
 	case BPF_HDR_START_NET:
-		ptr = skb_network_header(skb) + offset;
+		ptr = net + offset;
 		break;
 	default:
 		goto err_clear;
 	}
 
-	if (likely(ptr >= skb_mac_header(skb) &&
-		   ptr + len <= skb_tail_pointer(skb))) {
+	if (likely(ptr >= mac && ptr + len <= end)) {
 		memcpy(to, ptr, len);
 		return 0;
 	}
-- 
2.9.5