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 @@ -6223,7 +6223,8 @@ 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 @@ -954,7 +954,7 @@ 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; } @@ -962,7 +962,7 @@ 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 @@ -10540,7 +10540,8 @@ 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));