dccp: Initialisation and type-checking of feature sysctls

This patch takes care of initialising and type-checking sysctls
related to feature negotiation. Type checking is important since some
of the sysctls now directly impact the feature-negotiation process.

The sysctls are initialised with the known default values for each
feature.  For the type-checking the value constraints from RFC 4340
are used:

 * Sequence Window uses the specified Wmin=32, the maximum is ulong (4 bytes),
   tested and confirmed that it works up to 4294967295 - for Gbps speed;
 * Ack Ratio is between 0 .. 0xffff (2-byte unsigned integer);
 * CCIDs are between 0 .. 255;
 * request_retries, retries1, retries2 also between 0..255 for good measure;
 * tx_qlen is checked to be non-negative;
 * sync_ratelimit remains as before.

Notes:
------
 1. Die s@sysctl_dccp_feat@sysctl_dccp@g since the sysctls are now in feat.c.
 2. As pointed out by Arnaldo, the pattern of type-checking repeats itself in
    other places, sometimes with exactly the same kind of definitions (e.g.
    "static int zero;"). It may be a good idea (kernel janitors?) to consolidate
    type checking. For the sake of keeping the changeset small and in order not
    to affect other subsystems, I have not strived to generalise here.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 46 insertions, 23 deletions

diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 04ae91898a68..44a5bc6f6785 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -95,9 +95,6 @@ extern void dccp_time_wait(struct sock *sk, int state, int timeo);
 extern int  sysctl_dccp_request_retries;
 extern int  sysctl_dccp_retries1;
 extern int  sysctl_dccp_retries2;
-extern int  sysctl_dccp_feat_sequence_window;
-extern int  sysctl_dccp_feat_rx_ccid;
-extern int  sysctl_dccp_feat_tx_ccid;
 extern int  sysctl_dccp_tx_qlen;
 extern int  sysctl_dccp_sync_ratelimit;
 
diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 7303f79705d2..12006e9b2472 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -25,6 +25,11 @@
 #include "ccid.h"
 #include "feat.h"
 
+/* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
+unsigned long   sysctl_dccp_sequence_window __read_mostly = 100;
+int             sysctl_dccp_rx_ccid         __read_mostly = 2,
+                sysctl_dccp_tx_ccid         __read_mostly = 2;
+
 /*
  * Feature activation handlers.
  *
@@ -1146,7 +1151,7 @@ int dccp_feat_init(struct sock *sk)
 
         /* Non-negotiable (NN) features */
         rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
-                                    sysctl_dccp_feat_sequence_window);
+                                    sysctl_dccp_sequence_window);
         if (rc)
                 return rc;
 
@@ -1172,8 +1177,8 @@ int dccp_feat_init(struct sock *sk)
             ccid_get_builtin_ccids(&rx.val, &rx.len))
                 return -ENOBUFS;
 
-        if (!dccp_feat_prefer(sysctl_dccp_feat_tx_ccid, tx.val, tx.len) ||
-            !dccp_feat_prefer(sysctl_dccp_feat_rx_ccid, rx.val, rx.len))
+        if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
+            !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
                 goto free_ccid_lists;
 
         rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);
diff --git a/net/dccp/feat.h b/net/dccp/feat.h
index 5e7b8481cd04..40aa7a10bd5f 100644
--- a/net/dccp/feat.h
+++ b/net/dccp/feat.h
@@ -100,6 +100,13 @@ struct ccid_dependency {
         u8      val;
 };
 
+/*
+ * Sysctls to seed defaults for feature negotiation
+ */
+extern unsigned long sysctl_dccp_sequence_window;
+extern int           sysctl_dccp_rx_ccid;
+extern int           sysctl_dccp_tx_ccid;
+
 #ifdef CONFIG_IP_DCCP_DEBUG
 extern const char *dccp_feat_typename(const u8 type);
 extern const char *dccp_feat_name(const u8 feat);
@@ -114,6 +121,7 @@ static inline void dccp_feat_debug(const u8 type, const u8 feat, const u8 val)
 #endif /* CONFIG_IP_DCCP_DEBUG */
 
 extern int  dccp_feat_init(struct sock *sk);
+extern void dccp_feat_initialise_sysctls(void);
 extern int  dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
                                   u8 const *list, u8 len);
 extern int  dccp_feat_register_nn(struct sock *sk, u8 feat, u64 val);
diff --git a/net/dccp/options.c b/net/dccp/options.c
index 7b1165c21f51..3e2726c7182d 100644
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -23,10 +23,6 @@
 #include "dccp.h"
 #include "feat.h"
 
-int sysctl_dccp_feat_sequence_window = DCCPF_INITIAL_SEQUENCE_WINDOW;
-int sysctl_dccp_feat_rx_ccid          = DCCPF_INITIAL_CCID;
-int sysctl_dccp_feat_tx_ccid          = DCCPF_INITIAL_CCID;
-
 u64 dccp_decode_value_var(const u8 *bf, const u8 len)
 {
         u64 value = 0;
diff --git a/net/dccp/sysctl.c b/net/dccp/sysctl.c
index 018e210875e1..a5a1856234e7 100644
--- a/net/dccp/sysctl.c
+++ b/net/dccp/sysctl.c
@@ -18,55 +18,72 @@
 #error This file should not be compiled without CONFIG_SYSCTL defined
 #endif
 
+/* Boundary values */
+static int              zero     = 0,
+                        u8_max   = 0xFF;
+static unsigned long    seqw_min = 32;
+
 static struct ctl_table dccp_default_table[] = {
         {
                 .procname       = "seq_window",
-                .data           = &sysctl_dccp_feat_sequence_window,
-                .maxlen         = sizeof(sysctl_dccp_feat_sequence_window),
+                .data           = &sysctl_dccp_sequence_window,
+                .maxlen         = sizeof(sysctl_dccp_sequence_window),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_doulongvec_minmax,
+                .extra1         = &seqw_min,            /* RFC 4340, 7.5.2 */
         },
         {
                 .procname       = "rx_ccid",
-                .data           = &sysctl_dccp_feat_rx_ccid,
-                .maxlen         = sizeof(sysctl_dccp_feat_rx_ccid),
+                .data           = &sysctl_dccp_rx_ccid,
+                .maxlen         = sizeof(sysctl_dccp_rx_ccid),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &u8_max,              /* RFC 4340, 10. */
         },
         {
                 .procname       = "tx_ccid",
-                .data           = &sysctl_dccp_feat_tx_ccid,
-                .maxlen         = sizeof(sysctl_dccp_feat_tx_ccid),
+                .data           = &sysctl_dccp_tx_ccid,
+                .maxlen         = sizeof(sysctl_dccp_tx_ccid),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &u8_max,              /* RFC 4340, 10. */
         },
         {
                 .procname       = "request_retries",
                 .data           = &sysctl_dccp_request_retries,
                 .maxlen         = sizeof(sysctl_dccp_request_retries),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &u8_max,
         },
         {
                 .procname       = "retries1",
                 .data           = &sysctl_dccp_retries1,
                 .maxlen         = sizeof(sysctl_dccp_retries1),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &u8_max,
         },
         {
                 .procname       = "retries2",
                 .data           = &sysctl_dccp_retries2,
                 .maxlen         = sizeof(sysctl_dccp_retries2),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &u8_max,
         },
         {
                 .procname       = "tx_qlen",
                 .data           = &sysctl_dccp_tx_qlen,
                 .maxlen         = sizeof(sysctl_dccp_tx_qlen),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
         },
         {
                 .procname       = "sync_ratelimit",