netfilter: nf_tables: fix nft_cmp_fast failure on big endian for size < 4 (b855d416) · Commits · 戴 / test

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:

Patrick McHardy <kaber@trash.net> Signed-off-by:

Pablo Neira Ayuso <pablo@netfilter.org>

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;

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