Re: [PATCH 06/11] sysctl: Add size to register_net_sysctl function

On Wed, Jun 21, 2023 at 12:47:30PM +0300, Dan Carpenter wrote:
> The patchset doesn't include the actual interesting changes, just a
> bunch of mechanical prep work.
> 
> On Wed, Jun 21, 2023 at 11:09:55AM +0200, Joel Granados wrote:
> > diff --git a/net/ieee802154/6lowpan/reassembly.c b/net/ieee802154/6lowpan/reassembly.c
> > index a91283d1e5bf..7b717434368c 100644
> > --- a/net/ieee802154/6lowpan/reassembly.c
> > +++ b/net/ieee802154/6lowpan/reassembly.c
> > @@ -379,7 +379,8 @@ static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
> >  	table[1].extra2	= &ieee802154_lowpan->fqdir->high_thresh;
> >  	table[2].data	= &ieee802154_lowpan->fqdir->timeout;
> >  
> > -	hdr = register_net_sysctl(net, "net/ieee802154/6lowpan", table);
> > +	hdr = register_net_sysctl(net, "net/ieee802154/6lowpan", table,
> > +				  ARRAY_SIZE(lowpan_frags_ns_ctl_table));
> 
> For example, in lowpan_frags_ns_sysctl_register() the sentinel is
> sometimes element zero if the user doesn't have enough permissions.  I
> would want to ensure that was handled correctly, but that's going to be
> done later in a completely different patchset.  I'm definitely not going
> to remember to check.

On reflecting the patch is obviously wrong.  It should be pass zero as
table_size in that case.  See diff at the end.

There is a similar bug in neigh_sysctl_register() where we use memset to
zero out the whole table.  And another in __ip_vs_lblc_init().  I used
the smatch cross function database
	`smdb.py where ctl_table procname | grep '(null)' | grep min-max`
to make a list of functions which set procname to zero.

Probably we should add a WARN_ON() if procname is zero in the new code
which doesn't use sentinels.

regards,
dan carpenter

drivers/char/random.c          | proc_do_uuid                   | (struct ctl_table)->procname | 0
fs/proc/proc_sysctl.c          | new_dir                        | (struct ctl_table)->procname | 48,3906148897379000352
fs/proc/proc_sysctl.c          | new_links                      | (struct ctl_table)->procname | 4096-ptr_max
arch/arm64/kernel/fpsimd.c     | vec_proc_do_default_vl         | (struct ctl_table)->procname | 0
arch/arm64/kernel/armv8_deprecated.c | register_insn_emulation        | (struct ctl_table)->procname | 0-u64max
kernel/sysctl-test.c           | sysctl_test_api_dointvec_null_tbl_data | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_api_dointvec_table_maxlen_unset | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_api_dointvec_table_len_is_zero | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_api_dointvec_table_read_but_position_set | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_dointvec_read_happy_single_positive | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_dointvec_read_happy_single_negative | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_dointvec_write_happy_single_positive | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_dointvec_write_happy_single_negative | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_api_dointvec_write_single_less_int_min | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl-test.c           | sysctl_test_api_dointvec_write_single_greater_int_max | (struct ctl_table)->procname | 7612622206476333056
kernel/sysctl.c                | proc_do_static_key             | (struct ctl_table)->procname | 0
kernel/kexec_core.c            | kexec_limit_handler            | (struct ctl_table)->procname | 0
kernel/bpf/syscall.c           | bpf_stats_handler              | (struct ctl_table)->procname | 0
net/core/sysctl_net_core.c     | rps_sock_flow_sysctl           | (struct ctl_table)->procname | 0
net/core/sysctl_net_core.c     | set_default_qdisc              | (struct ctl_table)->procname | 0
net/core/neighbour.c           | neigh_sysctl_register          | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_lblc.c | __ip_vs_lblc_init              | (struct ctl_table)->procname | 0-u64max
net/netfilter/ipvs/ip_vs_lblcr.c | __ip_vs_lblcr_init             | (struct ctl_table)->procname | 0-u64max
net/netfilter/ipvs/ip_vs_ctl.c | proc_do_defense_mode           | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_ctl.c | proc_do_sync_threshold         | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_ctl.c | proc_do_sync_ports             | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_ctl.c | ipvs_proc_est_nice             | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_ctl.c | ipvs_proc_run_estimation       | (struct ctl_table)->procname | 0
net/netfilter/ipvs/ip_vs_ctl.c | ip_vs_control_net_init_sysctl  | (struct ctl_table)->procname | 0-u64max
net/netfilter/nf_log.c         | netfilter_log_sysctl_init      | (struct ctl_table)->procname | 0-u64max
net/sctp/sysctl.c              | proc_sctp_do_hmac_alg          | (struct ctl_table)->procname | 0
net/sctp/sysctl.c              | proc_sctp_do_rto_min           | (struct ctl_table)->procname | 0
net/sctp/sysctl.c              | proc_sctp_do_rto_max           | (struct ctl_table)->procname | 0
net/sctp/sysctl.c              | proc_sctp_do_auth              | (struct ctl_table)->procname | 0
net/sctp/sysctl.c              | proc_sctp_do_udp_port          | (struct ctl_table)->procname | 0
net/sctp/sysctl.c              | proc_sctp_do_probe_interval    | (struct ctl_table)->procname | 0
net/ipv6/route.c               | ipv6_route_sysctl_init         | (struct ctl_table)->procname | 0-u64max
net/ipv6/addrconf.c            | addrconf_sysctl_addr_gen_mode  | (struct ctl_table)->procname | 0
net/ieee802154/6lowpan/reassembly.c | lowpan_frags_ns_sysctl_register | (struct ctl_table)->procname | 0-u64max
net/xfrm/xfrm_sysctl.c         | xfrm_sysctl_init               | (struct ctl_table)->procname | 0-u64max
net/phonet/sysctl.c            | proc_local_port_range          | (struct ctl_table)->procname | 0
net/ipv4/route.c               | sysctl_route_net_init          | (struct ctl_table)->procname | 0-u64max
net/ipv4/sysctl_net_ipv4.c     | ipv4_local_port_range          | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | ipv4_privileged_ports          | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | ipv4_ping_group_range          | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_tcp_congestion_control    | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_tcp_available_congestion_control | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_allowed_congestion_control | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_tcp_fastopen_key          | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_tcp_available_ulp         | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_tcp_ehash_entries         | (struct ctl_table)->procname | 0
net/ipv4/sysctl_net_ipv4.c     | proc_udp_hash_entries          | (struct ctl_table)->procname | 0

diff --git a/net/ieee802154/6lowpan/reassembly.c b/net/ieee802154/6lowpan/reassembly.c
index a91283d1e5bf..749238d38014 100644
--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -360,6 +360,7 @@ static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
 	struct ctl_table_header *hdr;
 	struct netns_ieee802154_lowpan *ieee802154_lowpan =
 		net_ieee802154_lowpan(net);
+	size_t table_size = ARRAY_SIZE(lowpan_frags_ns_ctl_table);
 
 	table = lowpan_frags_ns_ctl_table;
 	if (!net_eq(net, &init_net)) {
@@ -369,8 +370,10 @@ static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
 			goto err_alloc;
 
 		/* Don't export sysctls to unprivileged users */
-		if (net->user_ns != &init_user_ns)
+		if (net->user_ns != &init_user_ns) {
 			table[0].procname = NULL;
+			table_size = 0;
+		}
 	}
 
 	table[0].data	= &ieee802154_lowpan->fqdir->high_thresh;
@@ -379,7 +382,7 @@ static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
 	table[1].extra2	= &ieee802154_lowpan->fqdir->high_thresh;
 	table[2].data	= &ieee802154_lowpan->fqdir->timeout;
 
-	hdr = register_net_sysctl(net, "net/ieee802154/6lowpan", table);
+	hdr = register_net_sysctl(net, "net/ieee802154/6lowpan", table, table_size);
 	if (hdr == NULL)
 		goto err_reg;