netfilter: conntrack: Bound nf_conntrack sysctl writes

nf_conntrack_max and nf_conntrack_expect_max sysctls were authorized to
be written any negative value, which would then be stored in the
unsigned int variables nf_conntrack_max and nf_ct_expect_max variables.

While the do_proc_dointvec_conv function is supposed to limit writing
handled by proc_dointvec proc_handler to INT_MAX. Such a negative value
being written in an unsigned int leads to a very high value, exceeding
this limit.

Moreover, the nf_conntrack_expect_max sysctl documentation specifies the
minimum value is 1.

The proc_handlers have thus been updated to proc_dointvec_minmax in
order to specify the following write bounds :

* Bound nf_conntrack_max sysctl writings between SYSCTL_ZERO
  and SYSCTL_INT_MAX.

* Bound nf_conntrack_expect_max sysctl writings between SYSCTL_ONE
  and SYSCTL_INT_MAX as defined in the sysctl documentation.

With this patch applied, sysctl writes outside the defined in the bound
will thus lead to a write error :

```
sysctl -w net.netfilter.nf_conntrack_expect_max=-1
sysctl: setting key "net.netfilter.nf_conntrack_expect_max": Invalid argument
```

Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 502cf10aab41d58aed19438bdbd173d154827561..2f666751c7e7c7d9ad884353978474dab5229390 100644 (file)
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -618,7 +618,9 @@ static struct ctl_table nf_ct_sysctl_table[] = {
                .data           = &nf_conntrack_max,
                .maxlen         = sizeof(int),
                .mode           = 0644,
-               .proc_handler   = proc_dointvec,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = SYSCTL_ZERO,
+               .extra2         = SYSCTL_INT_MAX,
        },
        [NF_SYSCTL_CT_COUNT] = {
                .procname       = "nf_conntrack_count",
@@ -654,7 +656,9 @@ static struct ctl_table nf_ct_sysctl_table[] = {
                .data           = &nf_ct_expect_max,
                .maxlen         = sizeof(int),
                .mode           = 0644,
-               .proc_handler   = proc_dointvec,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = SYSCTL_ONE,
+               .extra2         = SYSCTL_INT_MAX,
        },
        [NF_SYSCTL_CT_ACCT] = {
                .procname       = "nf_conntrack_acct",
@@ -947,7 +951,9 @@ static struct ctl_table nf_ct_netfilter_table[] = {
                .data           = &nf_conntrack_max,
                .maxlen         = sizeof(int),
                .mode           = 0644,
-               .proc_handler   = proc_dointvec,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = SYSCTL_ZERO,
+               .extra2         = SYSCTL_INT_MAX,
        },
 };