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@xxxxxxxxxxx>
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
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 4a2f7041ebae..a7f0ddedac1f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5574,7 +5574,8 @@ 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 a06931c27eeb..99a05199a806 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8265,6 +8265,7 @@ 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;
@@ -8276,7 +8277,6 @@ 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):
@@ -8285,6 +8285,14 @@ 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;
--
2.31.1
