[PATCH AUTOSEL 4.19 171/172] net/filter: Permit reading NET in load_bytes_relative when MAC not set

Sasha Levin
2020-06-18T01:29:01Z

From: YiFei Zhu <zhuyifei1999@gmail.com>

[ Upstream commit 0f5d82f187e1beda3fe7295dfc500af266a5bd80 ]

Added a check in the switch case on start_header that checks for
the existence of the header, and in the case that MAC is not set
and the caller requests for MAC, -EFAULT. If the caller requests
for NET then MAC's existence is completely ignored.

There is no function to check NET header's existence and as far
as cgroup_skb/egress is concerned it should always be set.

Removed for ptr >= the start of header, considering offset is
bounded unsigned and should always be true. len <= end - mac is
redundant to ptr + len <= end.

Fixes: 3eee1f75f2b9 ("bpf: fix bpf_skb_load_bytes_relative pkt length check")
Signed-off-by: YiFei Zhu <zhuyifei@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/76bb820ddb6a95f59a772ecbd8c8a336f646b362.1591812755.git.zhuyifei@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/filter.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 40b3af05c883..b5521b60a2d4 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1730,25 +1730,27 @@ 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;
+ u8 *start, *ptr;

- if (unlikely(offset > 0xffff || len > (end - mac)))
+ if (unlikely(offset > 0xffff))
goto err_clear;

switch (start_header) {
case BPF_HDR_START_MAC:
- ptr = mac + offset;
+ if (unlikely(!skb_mac_header_was_set(skb)))
+ goto err_clear;
+ start = skb_mac_header(skb);
break;
case BPF_HDR_START_NET:
- ptr = net + offset;
+ start = skb_network_header(skb);
break;
default:
goto err_clear;
}

- if (likely(ptr >= mac && ptr + len <= end)) {
+ ptr = start + offset;
+
+ if (likely(ptr + len <= end)) {
memcpy(to, ptr, len);
return 0;
}
--
2.25.1