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>

1 files changed, 9 insertions, 3 deletions

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 502cf10aab41..2f666751c7e7 100644
--- 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,
 	},
 };