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Commit 233577a2 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

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: default avatarDenis Kirjanov <kda@linux-powerpc.org>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Acked-by: default avatarDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ac7a04c3

arch/mips/net/bpf_jit.c

+1 −26
Original line number Diff line number Diff line
@@ -765,27 +765,6 @@ static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset) 
	return (u64)err << 32 | ntohl(ret);

}



#ifdef __BIG_ENDIAN_BITFIELD

#define PKT_TYPE_MAX	(7 << 5)

#else

#define PKT_TYPE_MAX	7

#endif

static 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 pkt_type_offset(), as pkt_type couldn't be found\n");

	return -1;

}



static int build_body(struct jit_ctx *ctx)

{

	void *load_func[] = {jit_get_skb_b, jit_get_skb_h, jit_get_skb_w};
@@ -1332,11 +1311,7 @@ static int build_body(struct jit_ctx *ctx) 
		case BPF_ANC | SKF_AD_PKTTYPE:

			ctx->flags |= SEEN_SKB;



			off = pkt_type_offset();



			if (off < 0)

				return -1;

			emit_load_byte(r_tmp, r_skb, off, ctx);

			emit_load_byte(r_tmp, r_skb, PKT_TYPE_OFFSET(), ctx);

			/* Keep only the last 3 bits */

			emit_andi(r_A, r_tmp, PKT_TYPE_MAX, ctx);

#ifdef __BIG_ENDIAN_BITFIELD

arch/s390/net/bpf_jit_comp.c

+1 −34
Original line number Diff line number Diff line
@@ -227,37 +227,6 @@ static void bpf_jit_epilogue(struct bpf_jit *jit) 
	EMIT2(0x07fe);

}



/* Helper to find the offset of pkt_type in sk_buff

 * Make sure its still a 3bit field starting at the MSBs within a byte.

 */

#define PKT_TYPE_MAX 0xe0

static int pkt_type_offset;



static int __init bpf_pkt_type_offset_init(void)

{

	struct sk_buff skb_probe = {

		.pkt_type = ~0,

	};

	char *ct = (char *)&skb_probe;

	int off;



	pkt_type_offset = -1;

	for (off = 0; off < sizeof(struct sk_buff); off++) {

		if (!ct[off])

			continue;

		if (ct[off] == PKT_TYPE_MAX)

			pkt_type_offset = off;

		else {

			/* Found non matching bit pattern, fix needed. */

			WARN_ON_ONCE(1);

			pkt_type_offset = -1;

			return -1;

		}

	}

	return 0;

}

device_initcall(bpf_pkt_type_offset_init);



/*

 * make sure we dont leak kernel information to user

 */
@@ -757,12 +726,10 @@ load_abs: if ((int) K < 0) 
		}

		break;

	case BPF_ANC | SKF_AD_PKTTYPE:

		if (pkt_type_offset < 0)

			goto out;

		/* lhi %r5,0 */

		EMIT4(0xa7580000);

		/* ic %r5,<d(pkt_type_offset)>(%r2) */

		EMIT4_DISP(0x43502000, pkt_type_offset);

		EMIT4_DISP(0x43502000, PKT_TYPE_OFFSET());

		/* srl %r5,5 */

		EMIT4_DISP(0x88500000, 5);

		break;

include/linux/skbuff.h

+10 −0
Original line number Diff line number Diff line
@@ -548,6 +548,16 @@ struct sk_buff { 
				ip_summed:2,

				nohdr:1,

				nfctinfo:3;



/* if you move pkt_type around you also must adapt those constants */

#ifdef __BIG_ENDIAN_BITFIELD

#define PKT_TYPE_MAX	(7 << 5)

#else

#define PKT_TYPE_MAX	7

#endif

#define PKT_TYPE_OFFSET()	offsetof(struct sk_buff, __pkt_type_offset)



	__u8			__pkt_type_offset[0];

	__u8			pkt_type:3,

				fclone:2,

				ipvs_property:1,

net/core/filter.c

+2 −29
Original line number Diff line number Diff line
@@ -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++;