[PATCH 5.16 264/285] bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide

Greg Kroah-Hartman
2022-04-12T08:25:57Z

From: Jakub Sitnicki <jakub@cloudflare.com>

commit 9a69e2b385f443f244a7e8b8bcafe5ccfb0866b4 upstream.

remote_port is another case of a BPF context field documented as a 32-bit
value in network byte order for which the BPF context access converter
generates a load of a zero-padded 16-bit integer in network byte order.

First such case was dst_port in bpf_sock which got addressed in commit
4421a582718a ("bpf: Make dst_port field in struct bpf_sock 16-bit wide").

Loading 4-bytes from the remote_port offset and converting the value with
bpf_ntohl() leads to surprising results, as the expected value is shifted
by 16 bits.

Reduce the confusion by splitting the field in two - a 16-bit field holding
a big-endian integer, and a 16-bit zero-padding anonymous field that
follows it.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220209184333.654927-2-jakub@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/uapi/linux/bpf.h | 3 ++-
net/bpf/test_run.c | 4 ++--
net/core/filter.c | 3 ++-
3 files changed, 6 insertions(+), 4 deletions(-)

--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6293,7 +6293,8 @@ struct bpf_sk_lookup {
__u32 protocol; /* IP protocol (IPPROTO_TCP, IPPROTO_UDP) */
__u32 remote_ip4; /* Network byte order */
__u32 remote_ip6[4]; /* Network byte order */
- __u32 remote_port; /* Network byte order */
+ __be16 remote_port; /* Network byte order */
+ __u16 :16; /* Zero padding */
__u32 local_ip4; /* Network byte order */
__u32 local_ip6[4]; /* Network byte order */
__u32 local_port; /* Host byte order */
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -960,7 +960,7 @@ int bpf_prog_test_run_sk_lookup(struct b
if (!range_is_zero(user_ctx, offsetofend(typeof(*user_ctx), local_port), sizeof(*user_ctx)))
goto out;

- if (user_ctx->local_port > U16_MAX || user_ctx->remote_port > U16_MAX) {
+ if (user_ctx->local_port > U16_MAX) {
ret = -ERANGE;
goto out;
}
@@ -968,7 +968,7 @@ int bpf_prog_test_run_sk_lookup(struct b
ctx.family = (u16)user_ctx->family;
ctx.protocol = (u16)user_ctx->protocol;
ctx.dport = (u16)user_ctx->local_port;
- ctx.sport = (__force __be16)user_ctx->remote_port;
+ ctx.sport = user_ctx->remote_port;

switch (ctx.family) {
case AF_INET:
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -10563,7 +10563,8 @@ static bool sk_lookup_is_valid_access(in
case bpf_ctx_range(struct bpf_sk_lookup, local_ip4):
case bpf_ctx_range_till(struct bpf_sk_lookup, remote_ip6[0], remote_ip6[3]):
case bpf_ctx_range_till(struct bpf_sk_lookup, local_ip6[0], local_ip6[3]):
- case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
+ case offsetof(struct bpf_sk_lookup, remote_port) ...
+ offsetof(struct bpf_sk_lookup, local_ip4) - 1:
case bpf_ctx_range(struct bpf_sk_lookup, local_port):
bpf_ctx_record_field_size(info, sizeof(__u32));
return bpf_ctx_narrow_access_ok(off, size, sizeof(__u32));