netfilter: allow hooks to pass error code back up the stack

SELinux would like to pass certain fatal errors back up the stack.  This patch
implements the generic netfilter support for this functionality.

Based-on-patch-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 03317c8d4077..1893837b3966 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -33,6 +33,8 @@
 
 #define NF_QUEUE_NR(x) ((((x) << NF_VERDICT_BITS) & NF_VERDICT_QMASK) | NF_QUEUE)
 
+#define NF_DROP_ERR(x) (((-x) << NF_VERDICT_BITS) | NF_DROP)
+
 /* only for userspace compatibility */
 #ifndef __KERNEL__
 /* Generic cache responses from hook functions.
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 85dabb86be6f..32fcbe290c04 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -173,9 +173,11 @@ next_hook:
                              outdev, &elem, okfn, hook_thresh);
         if (verdict == NF_ACCEPT || verdict == NF_STOP) {
                 ret = 1;
-        } else if (verdict == NF_DROP) {
+        } else if ((verdict & NF_VERDICT_MASK) == NF_DROP) {
                 kfree_skb(skb);
-                ret = -EPERM;
+                ret = -(verdict >> NF_VERDICT_BITS);
+                if (ret == 0)
+                        ret = -EPERM;
         } else if ((verdict & NF_VERDICT_MASK) == NF_QUEUE) {
                 if (!nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
                               verdict >> NF_VERDICT_BITS))