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@xxxxxxxxx>
---
include/net/netfilter/nf_tables_core.h | 10 ++++++++++
net/netfilter/nf_tables_core.c | 3 +--
net/netfilter/nft_cmp.c | 2 +-
3 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/net/netfilter/nf_tables_core.h b/include/net/netfilter/nf_tables_core.h
index cf2b7ae..a75fc8e 100644
--- 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 90998a6..8041053 100644
--- 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 954925d..e2b3f51 100644
--- 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;
--
1.9.0
--
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