netdev - [Patch bpf 1/2] bpf: check negative offsets in __bpf_skb_min

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>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241107034141.250815-1-xiyou.wangcong@gmail.com>
Date: Wed,  6 Nov 2024 19:41:40 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: bpf@...r.kernel.org,
	Cong Wang <cong.wang@...edance.com>,
	John Fastabend <john.fastabend@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [Patch bpf 1/2] bpf: check negative offsets in __bpf_skb_min_len()

From: Cong Wang <cong.wang@...edance.com>

skb_transport_offset() and skb_transport_offset() can be negative when
they are called after we pull the transport header, for example, when
we use eBPF sockmap (aka at the point of ->sk_data_ready()).

__bpf_skb_min_len() uses an unsigned int to get these offsets, this
leads to a very large number which then causes bpf_skb_change_tail()
failed unexpectedly.

Fix this by using a signed int to get these offsets and ensure the
minimum is at least zero.

Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper")
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/core/filter.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index e31ee8be2de0..fd263c22944d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3737,13 +3737,22 @@ static const struct bpf_func_proto bpf_skb_adjust_room_proto = {
 
 static u32 __bpf_skb_min_len(const struct sk_buff *skb)
 {
-	u32 min_len = skb_network_offset(skb);
+	int offset = skb_network_offset(skb);
+	u32 min_len = 0;
 
-	if (skb_transport_header_was_set(skb))
-		min_len = skb_transport_offset(skb);
-	if (skb->ip_summed == CHECKSUM_PARTIAL)
-		min_len = skb_checksum_start_offset(skb) +
-			  skb->csum_offset + sizeof(__sum16);
+	if (offset > 0)
+		min_len = offset;
+	if (skb_transport_header_was_set(skb)) {
+		offset = skb_transport_offset(skb);
+		if (offset > 0)
+			min_len = offset;
+	}
+	if (skb->ip_summed == CHECKSUM_PARTIAL) {
+		offset = skb_checksum_start_offset(skb) +
+			 skb->csum_offset + sizeof(__sum16);
+		if (offset > 0)
+			min_len = offset;
+	}
 	return min_len;
 }
 
-- 
2.34.1