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Commit b855d416 authored by Patrick McHardy's avatar Patrick McHardy Committed by Pablo Neira Ayuso
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netfilter: nf_tables: fix nft_cmp_fast failure on big endian for size < 4 



nft_cmp_fast is used for equality comparisions of size <= 4. For
comparisions of size < 4 byte a mask is calculated that is applied to
both the data from userspace (during initialization) and the register
value (during runtime). Both values are stored using (in effect) memcpy
to a memory area that is then interpreted as u32 by nft_cmp_fast.

This works fine on little endian since smaller types have the same base
address, however on big endian this is not true and the smaller types
are interpreted as a big number with trailing zero bytes.

The mask therefore must not include the lower bytes, but the higher bytes
on big endian. Add a helper function that does a cpu_to_le32 to switch
the bytes on big endian. Since we're dealing with a mask of just consequitive
bits, this works out fine.

Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent ee214d54

include/net/netfilter/nf_tables_core.h

+10 −0
Original line number Diff line number Diff line
@@ -13,6 +13,16 @@ struct nft_cmp_fast_expr { 
	u8			len;

};



/* Calculate the mask for the nft_cmp_fast expression. On big endian the

 * mask needs to include the *upper* bytes when interpreting that data as

 * something smaller than the full u32, therefore a cpu_to_le32 is done.

 */

static inline u32 nft_cmp_fast_mask(unsigned int len)

{

	return cpu_to_le32(~0U >> (FIELD_SIZEOF(struct nft_cmp_fast_expr,

						data) * BITS_PER_BYTE - len));

}



extern const struct nft_expr_ops nft_cmp_fast_ops;



int nft_cmp_module_init(void);

net/netfilter/nf_tables_core.c

+1 −2
Original line number Diff line number Diff line
@@ -25,9 +25,8 @@ static void nft_cmp_fast_eval(const struct nft_expr *expr, 
			      struct nft_data data[NFT_REG_MAX + 1])

{

	const struct nft_cmp_fast_expr *priv = nft_expr_priv(expr);

	u32 mask;

	u32 mask = nft_cmp_fast_mask(priv->len);



	mask = ~0U >> (sizeof(priv->data) * BITS_PER_BYTE - priv->len);

	if ((data[priv->sreg].data[0] & mask) == priv->data)

		return;

	data[NFT_REG_VERDICT].verdict = NFT_BREAK;

net/netfilter/nft_cmp.c

+1 −1
Original line number Diff line number Diff line
@@ -128,7 +128,7 @@ static int nft_cmp_fast_init(const struct nft_ctx *ctx, 
	BUG_ON(err < 0);

	desc.len *= BITS_PER_BYTE;



	mask = ~0U >> (sizeof(priv->data) * BITS_PER_BYTE - desc.len);

	mask = nft_cmp_fast_mask(desc.len);

	priv->data = data.data[0] & mask;

	priv->len  = desc.len;

	return 0;