netfilter: nf_tables: fix mismatch in big-endian system

Currently, there are two different methods to store an u16 integer to
the u32 data register. For example:
  u32 *dest = &regs->data[priv->dreg];
  1. *dest = 0; *(u16 *) dest = val_u16;
  2. *dest = val_u16;

For method 1, the u16 value will be stored like this, either in
big-endian or little-endian system:
  0          15           31
  +-+-+-+-+-+-+-+-+-+-+-+-+
  |   Value   |     0     |
  +-+-+-+-+-+-+-+-+-+-+-+-+

For method 2, in little-endian system, the u16 value will be the same
as listed above. But in big-endian system, the u16 value will be stored
like this:
  0          15           31
  +-+-+-+-+-+-+-+-+-+-+-+-+
  |     0     |   Value   |
  +-+-+-+-+-+-+-+-+-+-+-+-+

So later we use "memcmp(&regs->data[priv->sreg], data, 2);" to do
compare in nft_cmp, nft_lookup expr ..., method 2 will get the wrong
result in big-endian system, as 0~15 bits will always be zero.

For the similar reason, when loading an u16 value from the u32 data
register, we should use "*(u16 *) sreg;" instead of "(u16)*sreg;",
the 2nd method will get the wrong value in the big-endian system.

So introduce some wrapper functions to store/load an u8 or u16
integer to/from the u32 data register, and use them in the right
place.

Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 2aa8a9d..70c5ca0 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -103,6 +103,35 @@ struct nft_regs {
 	};
 };
 
+/* Store/load an u16 or u8 integer to/from the u32 data register.
+ *
+ * Note, when using concatenations, register allocation happens at 32-bit
+ * level. So for store instruction, pad the rest part with zero to avoid
+ * garbage values.
+ */
+
+static inline void nft_reg_store16(u32 *dreg, u16 val)
+{
+	*dreg = 0;
+	*(u16 *)dreg = val;
+}
+
+static inline void nft_reg_store8(u32 *dreg, u8 val)
+{
+	*dreg = 0;
+	*(u8 *)dreg = val;
+}
+
+static inline u16 nft_reg_load16(u32 *sreg)
+{
+	return *(u16 *)sreg;
+}
+
+static inline u8 nft_reg_load8(u32 *sreg)
+{
+	return *(u8 *)sreg;
+}
+
 static inline void nft_data_copy(u32 *dst, const struct nft_data *src,
 				 unsigned int len)
 {