[PATCH 5.16 031/285] bpf: Make dst_port field in struct bpf_sock 16-bit wide

Greg Kroah-Hartman
2022-04-12T07:45:49Z

From: Jakub Sitnicki <jakub@cloudflare.com>

[ Upstream commit 4421a582718ab81608d8486734c18083b822390d ]

Menglong Dong reports that the documentation for the dst_port field in
struct bpf_sock is inaccurate and confusing. From the BPF program PoV, the
field is a zero-padded 16-bit integer in network byte order. The value
appears to the BPF user as if laid out in memory as so:

offsetof(struct bpf_sock, dst_port) + 0 <port MSB>
+ 8 <port LSB>
+16 0x00
+24 0x00

32-, 16-, and 8-bit wide loads from the field are all allowed, but only if
the offset into the field is 0.

32-bit wide loads from dst_port are especially confusing. The loaded value,
after converting to host byte order with bpf_ntohl(dst_port), contains the
port number in the upper 16-bits.

Remove the confusion by splitting the field into two 16-bit fields. For
backward compatibility, allow 32-bit wide loads from offsetof(struct
bpf_sock, dst_port).

While at it, allow loads 8-bit loads at offset [0] and [1] from dst_port.

Reported-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/r/20220130115518.213259-2-jakub@cloudflare.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/uapi/linux/bpf.h | 3 ++-
net/core/filter.c | 10 +++++++++-
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2b3c3f83076c..61bbaf340a89 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5414,7 +5414,8 @@ struct bpf_sock {
__u32 src_ip4;
__u32 src_ip6[4];
__u32 src_port; /* host byte order */
- __u32 dst_port; /* network byte order */
+ __be16 dst_port; /* network byte order */
+ __u16 :16; /* zero padding */
__u32 dst_ip4;
__u32 dst_ip6[4];
__u32 state;
diff --git a/net/core/filter.c b/net/core/filter.c
index d4cdf11656b3..4721ed65bcc5 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7975,6 +7975,7 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,
struct bpf_insn_access_aux *info)
{
const int size_default = sizeof(__u32);
+ int field_size;

if (off < 0 || off >= sizeof(struct bpf_sock))
return false;
@@ -7986,7 +7987,6 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,
case offsetof(struct bpf_sock, family):
case offsetof(struct bpf_sock, type):
case offsetof(struct bpf_sock, protocol):
- case offsetof(struct bpf_sock, dst_port):
case offsetof(struct bpf_sock, src_port):
case offsetof(struct bpf_sock, rx_queue_mapping):
case bpf_ctx_range(struct bpf_sock, src_ip4):
@@ -7995,6 +7995,14 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,
case bpf_ctx_range_till(struct bpf_sock, dst_ip6[0], dst_ip6[3]):
bpf_ctx_record_field_size(info, size_default);
return bpf_ctx_narrow_access_ok(off, size, size_default);
+ case bpf_ctx_range(struct bpf_sock, dst_port):
+ field_size = size == size_default ?
+ size_default : sizeof_field(struct bpf_sock, dst_port);
+ bpf_ctx_record_field_size(info, field_size);
+ return bpf_ctx_narrow_access_ok(off, size, field_size);
+ case offsetofend(struct bpf_sock, dst_port) ...
+ offsetof(struct bpf_sock, dst_ip4) - 1:
+ return false;
}

return size == size_default;
--
2.35.1