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>

1 files changed, 30 insertions, 13 deletions

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",