netfilter: reduce NF_VERDICT_MASK to 0xff

NF_VERDICT_MASK is currently 0xffff. This is because the upper
16 bits are used to store errno (for NF_DROP) or the queue number
(NF_QUEUE verdict).

As there are up to 0xffff different queues available, there is no more
room to store additional flags.

At the moment there are only 6 different verdicts, i.e. we can reduce
NF_VERDICT_MASK to 0xff to allow storing additional flags in the 0xff00 space.

NF_VERDICT_BITS would then be reduced to 8, but because the value is
exported to userspace, this might cause breakage; e.g.:

e.g. 'queuenr = (1 << NF_VERDICT_BITS) | NF_QUEUE'  would now break.

Thus, remove NF_VERDICT_BITS usage in the kernel and move the old value
to the 'userspace compat' section.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

3 files changed, 18 insertions, 8 deletions

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 0ab7ca787b22..78b73cc10216 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -24,16 +24,19 @@
 #define NF_MAX_VERDICT NF_STOP
 
 /* we overload the higher bits for encoding auxiliary data such as the queue
- * number. Not nice, but better than additional function arguments. */
-#define NF_VERDICT_MASK 0x0000ffff
-#define NF_VERDICT_BITS 16
+ * number or errno values. Not nice, but better than additional function
+ * arguments. */
+#define NF_VERDICT_MASK 0x000000ff
+
+/* extra verdict flags have mask 0x0000ff00 */
 
+/* queue number (NF_QUEUE) or errno (NF_DROP) */
 #define NF_VERDICT_QMASK 0xffff0000
 #define NF_VERDICT_QBITS 16
 
-#define NF_QUEUE_NR(x) ((((x) << NF_VERDICT_BITS) & NF_VERDICT_QMASK) | NF_QUEUE)
+#define NF_QUEUE_NR(x) ((((x) << 16) & NF_VERDICT_QMASK) | NF_QUEUE)
 
-#define NF_DROP_ERR(x) (((-x) << NF_VERDICT_BITS) | NF_DROP)
+#define NF_DROP_ERR(x) (((-x) << 16) | NF_DROP)
 
 /* only for userspace compatibility */
 #ifndef __KERNEL__
@@ -41,6 +44,9 @@
    <= 0x2000 is used for protocol-flags. */
 #define NFC_UNKNOWN 0x4000
 #define NFC_ALTERED 0x8000
+
+/* NF_VERDICT_BITS should be 8 now, but userspace might break if this changes */
+#define NF_VERDICT_BITS 16
 #endif
 
 enum nf_inet_hooks {
@@ -72,6 +78,10 @@ union nf_inet_addr {
 
 #ifdef __KERNEL__
 #ifdef CONFIG_NETFILTER
+static inline int NF_DROP_GETERR(int verdict)
+{
+        return -(verdict >> NF_VERDICT_QBITS);
+}
 
 static inline int nf_inet_addr_cmp(const union nf_inet_addr *a1,
                                    const union nf_inet_addr *a2)
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 0c5b796ef527..4d88e45b978e 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -175,12 +175,12 @@ next_hook:
                 ret = 1;
         } else if ((verdict & NF_VERDICT_MASK) == NF_DROP) {
                 kfree_skb(skb);
-                ret = -(verdict >> NF_VERDICT_BITS);
+                ret = NF_DROP_GETERR(verdict);
                 if (ret == 0)
                         ret = -EPERM;
         } else if ((verdict & NF_VERDICT_MASK) == NF_QUEUE) {
                 ret = nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
-                               verdict >> NF_VERDICT_BITS);
+                               verdict >> NF_VERDICT_QBITS);
                 if (ret < 0) {
                         if (ret == -ECANCELED)
                                 goto next_hook;
diff --git a/net/netfilter/nf_queue.c b/net/netfilter/nf_queue.c
index 5c4b730a2e68..ce1150d4a3f2 100644
--- a/net/netfilter/nf_queue.c
+++ b/net/netfilter/nf_queue.c
@@ -299,7 +299,7 @@ void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
         case NF_QUEUE:
                 err = __nf_queue(skb, elem, entry->pf, entry->hook,
                                  entry->indev, entry->outdev, entry->okfn,
-                                 verdict >> NF_VERDICT_BITS);
+                                 verdict >> NF_VERDICT_QBITS);
                 if (err < 0) {
                         if (err == -ECANCELED)
                                 goto next_hook;