In commit 9a69e2b385f4 ("bpf: Make remote_port field in struct
bpf_sk_lookup 16-bit wide") the remote_port field has been split up and
re-declared from u32 to be16.
However, the accompanying changes to the context access converter have not
been well thought through when it comes big-endian platforms.
Today 2-byte wide loads from offsetof(struct bpf_sk_lookup, remote_port)
are handled as narrow loads from a 4-byte wide field.
This by itself is not enough to create a problem, but when we combine
1. 32-bit wide access to ->remote_port backed by a 16-wide wide load, with
2. inherent difference between litte- and big-endian in how narrow loads
need have to be handled (see bpf_ctx_narrow_access_offset),
we get inconsistent results for a 2-byte loads from &ctx->remote_port on LE
and BE architectures. This in turn makes BPF C code for the common case of
2-byte load from ctx->remote_port not portable.
To rectify it, inform the context access converter that remote_port is
2-byte wide field, and only 1-byte loads need to be treated as narrow
loads.
At the same time, we special-case the 4-byte load from &ctx->remote_port to
continue handling it the same way as do today, in order to keep the
existing BPF programs working.
Fixes: 9a69e2b385f4 ("bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide")
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
net/core/filter.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 03655f2074ae..9b1e453baf6d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -10989,13 +10989,24 @@ static bool sk_lookup_is_valid_access(int off, int size,
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 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):
case bpf_ctx_range(struct bpf_sk_lookup, ingress_ifindex):
bpf_ctx_record_field_size(info, sizeof(__u32));
return bpf_ctx_narrow_access_ok(off, size, sizeof(__u32));
+ case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
+ /* Allow 4-byte access to 2-byte field for backward compatibility */
+ if (size == sizeof(__u32))
+ return off == offsetof(struct bpf_sk_lookup, remote_port);
+ bpf_ctx_record_field_size(info, sizeof(__be16));
+ return bpf_ctx_narrow_access_ok(off, size, sizeof(__be16));
+
+ case offsetofend(struct bpf_sk_lookup, remote_port) ...
+ offsetof(struct bpf_sk_lookup, local_ip4) - 1:
+ /* Allow access to zero padding for backward compatibility */
+ bpf_ctx_record_field_size(info, sizeof(__u16));
+ return bpf_ctx_narrow_access_ok(off, size, sizeof(__u16));
+
default:
return false;
}
@@ -11077,6 +11088,11 @@ static u32 sk_lookup_convert_ctx_access(enum bpf_access_type type,
sport, 2, target_size));
break;
+ case offsetofend(struct bpf_sk_lookup, remote_port):
+ *target_size = 2;
+ *insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
+ break;
+
case offsetof(struct bpf_sk_lookup, local_port):
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
bpf_target_off(struct bpf_sk_lookup_kern,
--
2.35.1
