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: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/net/netfilter/nf_tables_core.h b/include/net/netfilter/nf_tables_core.h
index cf2b7ae2b9d82b11cfa7a810130187e2c763881a..a75fc8e27cd698483232a3f3a379efc76308a905 100644 (file)
--- a/include/net/netfilter/nf_tables_core.h
+++ b/include/net/netfilter/nf_tables_core.h
@@ -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);

diff --git a/net/netfilter/nf_tables_core.c b/net/netfilter/nf_tables_core.c
index 90998a6ff8b9c1f10712e07d9b753e7d7d1bb2fd..804105391b9a903354ae9517d602c8c4638a8879 100644 (file)
--- a/net/netfilter/nf_tables_core.c
+++ b/net/netfilter/nf_tables_core.c
@@ -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;

diff --git a/net/netfilter/nft_cmp.c b/net/netfilter/nft_cmp.c
index 954925db414da8f973ecef119baab67dec229c12..e2b3f51c81f1df0289d75142689fcd109c351d0b 100644 (file)
--- a/net/netfilter/nft_cmp.c
+++ b/net/netfilter/nft_cmp.c
@@ -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;