net: filter: constify detection of pkt_type_offset

Currently we have 2 pkt_type_offset functions doing the same thing and
spread across the architecture files. Remove those and replace them
with a PKT_TYPE_OFFSET macro helper which gets the constant value from a
zero sized sk_buff member right in front of the bitfield with offsetof.
This new offset marker does not change size of struct sk_buff.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 29 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index dfc716ffa44b..601f28de7311 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -87,30 +87,6 @@ int sk_filter(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(sk_filter);
 
-/* Helper to find the offset of pkt_type in sk_buff structure. We want
- * to make sure its still a 3bit field starting at a byte boundary;
- * taken from arch/x86/net/bpf_jit_comp.c.
- */
-#ifdef __BIG_ENDIAN_BITFIELD
-#define PKT_TYPE_MAX    (7 << 5)
-#else
-#define PKT_TYPE_MAX    7
-#endif
-static unsigned int pkt_type_offset(void)
-{
-        struct sk_buff skb_probe = { .pkt_type = ~0, };
-        u8 *ct = (u8 *) &skb_probe;
-        unsigned int off;
-
-        for (off = 0; off < sizeof(struct sk_buff); off++) {
-                if (ct[off] == PKT_TYPE_MAX)
-                        return off;
-        }
-
-        pr_err_once("Please fix %s, as pkt_type couldn't be found!\n", __func__);
-        return -1;
-}
-
 static u64 __skb_get_pay_offset(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
 {
         return skb_get_poff((struct sk_buff *)(unsigned long) ctx);
@@ -190,11 +166,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
                 break;
 
         case SKF_AD_OFF + SKF_AD_PKTTYPE:
-                *insn = BPF_LDX_MEM(BPF_B, BPF_REG_A, BPF_REG_CTX,
-                                    pkt_type_offset());
-                if (insn->off < 0)
-                        return false;
-                insn++;
+                *insn++ = BPF_LDX_MEM(BPF_B, BPF_REG_A, BPF_REG_CTX,
+                                      PKT_TYPE_OFFSET());
                 *insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, PKT_TYPE_MAX);
 #ifdef __BIG_ENDIAN_BITFIELD
                 insn++;