[PATCH net v3 0/6] ipv6: fix error handling in disable_ipv6 sysctl

[PATCH net v3 0/6] ipv6: fix error handling in disable_ipv6 sysctl

[Fernando Fernandez Mancera]

While working on a different IPv6 patch series I have spotted multiple
minor bugs around sysctl error handling and notifications. In general,
they are not serious issues.

In addition, there is one more issue in forwarding sysctl as it does not
check for CAP_NET_ADMIN for the namespace. I am keeping that patch out
of this series and I am aiming it at the net-next tree once it re-opens.

During v3, Ido's pointed out that it is unnecessary to reset the
position pointer when the return value is negative as at
new_sync_write() the ppos is only advanced when ret return value is
positive. That means we can get rid of that operation in ipv4/ipv6
sysctls. That is going to be sent to net-next too.

Changes:
  v3: Patch 7: dropped from the series based on Ido's feedback

  v2: https://lore.kernel.org/netdev/20260620161850.7114-1-fmancera@suse.de/
      Patch 3: fix return code of addrconf_fixup_forwarding()
      Patch 5: acquire lock before calling proc_dointvec()
      Patch 7: new on this revision of the series

Fernando Fernandez Mancera (6):
  ipv6: fix error handling in disable_ipv6 sysctl
  ipv6: fix error handling in ignore_routes_with_linkdown sysctl
  ipv6: fix error handling in forwarding sysctl
  ipv6: fix error handling in disable_policy sysctl
  ipv6: fix state corruption during proxy_ndp sysctl restart
  ipv6: fix missing notification for ignore_routes_with_linkdown

 net/ipv6/addrconf.c | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

-- 
2.54.0

[PATCH net v3 1/6] ipv6: fix error handling in disable_ipv6 sysctl

[Fernando Fernandez Mancera]

When writing to the disable_ipv6 sysctl, if proc_dointvec() fails to
parse the input, it returns a negative error code. The current
implementation is overwriting that error for write operations.

This results in a silent failure, it returns a successful write although
the configuration was not modified at all. When modifying the "all"
variant it can also modify the configuration of existing interfaces to
the wrong value.

Fix this by checking the return value of proc_dointvec() and returning
early on failure.

Fixes: 56d417b12e57 ("IPv6: Add 'autoconf' and 'disable_ipv6' module parameters")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 1f21ccb55caa..c901b444a995 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -6467,6 +6467,8 @@ static int addrconf_sysctl_disable(const struct ctl_table *ctl, int write,
 	lctl.data = &val;
 
 	ret = proc_dointvec(&lctl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
 
 	if (write)
 		ret = addrconf_disable_ipv6(ctl, valp, val);
-- 
2.54.0

[PATCH net v3 2/6] ipv6: fix error handling in ignore_routes_with_linkdown sysctl

[Fernando Fernandez Mancera]

When writing to the ignore_routes_with_linkdown sysctl, if
proc_dointvec() fails to parse the input, it returns a negative error
code. The current implementation is overwriting that error for write
operations.

This results in a silent failure, it returns a successful write although
the configuration was not modified at all. When modifying the "all"
variant it can also modify the configuration of existing interfaces to
the wrong value.

Fix this by checking the return value of proc_dointvec() and returning
early on failure.

Fixes: 35103d11173b ("net: ipv6 sysctl option to ignore routes when nexthop link is down")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index c901b444a995..70058d971205 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -6671,6 +6671,8 @@ int addrconf_sysctl_ignore_routes_with_linkdown(const struct ctl_table *ctl,
 	lctl.data = &val;
 
 	ret = proc_dointvec(&lctl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
 
 	if (write)
 		ret = addrconf_fixup_linkdown(ctl, valp, val);
-- 
2.54.0

[PATCH net v3 3/6] ipv6: fix error handling in forwarding sysctl

[Fernando Fernandez Mancera]

When writing to the forwarding sysctl, if proc_dointvec() fails to parse
the input, it returns a negative error code. The current implementation
is overwriting that error for write operations.

This results in a silent failure, it returns a successful write although
the configuration was not modified at all. When modifying the "all"
variant it can also modify the configuration of existing interfaces to
the wrong value.

Fix this by checking the return value of proc_dointvec() and returning
early on failure. In addition, adjust return code of
addrconf_fixup_forwarding() for successful operation.

Fixes: b325fddb7f86 ("ipv6: Fix sysctl unregistration deadlock")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 70058d971205..d23a89b07eed 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -913,7 +913,7 @@ static int addrconf_fixup_forwarding(const struct ctl_table *table, int *p, int
 
 	if (newf)
 		rt6_purge_dflt_routers(net);
-	return 1;
+	return 0;
 }
 
 static void addrconf_linkdown_change(struct net *net, __s32 newf)
@@ -6370,6 +6370,8 @@ static int addrconf_sysctl_forward(const struct ctl_table *ctl, int write,
 	lctl.data = &val;
 
 	ret = proc_dointvec(&lctl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
 
 	if (write)
 		ret = addrconf_fixup_forwarding(ctl, valp, val);
-- 
2.54.0

[PATCH net v3 4/6] ipv6: fix error handling in disable_policy sysctl

[Fernando Fernandez Mancera]

When writing to the disable_policy sysctl, if proc_dointvec() fails to
parse the input, it returns a negative error code. The current
implementation is resetting the position argument even if an error
occurred during proc_dointvec() and not only during sysctl restart.

Fix this by checking the return value of proc_dointvec() and returning
early on failure.

Fixes: df789fe75206 ("ipv6: Provide ipv6 version of "disable_policy" sysctl")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d23a89b07eed..5d96cbf76134 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -6769,6 +6769,8 @@ static int addrconf_sysctl_disable_policy(const struct ctl_table *ctl, int write
 	lctl = *ctl;
 	lctl.data = &val;
 	ret = proc_dointvec(&lctl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
 
 	if (write && (*valp != val))
 		ret = addrconf_disable_policy(ctl, valp, val);
-- 
2.54.0

[PATCH net v3 5/6] ipv6: fix state corruption during proxy_ndp sysctl restart

[Fernando Fernandez Mancera]

When handling proxy_ndp, if rtnl_net_trylock() fails, the operation is
retried but as the value was already modified by the initial
proc_dointvec() call, the restarted syscall will read the newly modified
value as the 'old' state.

Fix this by taking the RTNL lock before parsing the input value if the
operation is a write.

Fixes: c92d5491a6d9 ("netconf: add support for IPv6 proxy_ndp")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5d96cbf76134..82b6f603faa0 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -6482,20 +6482,19 @@ static int addrconf_sysctl_disable(const struct ctl_table *ctl, int write,
 static int addrconf_sysctl_proxy_ndp(const struct ctl_table *ctl, int write,
 		void *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct net *net = ctl->extra2;
 	int *valp = ctl->data;
-	int ret;
 	int old, new;
+	int ret;
+
+	if (write && !rtnl_net_trylock(net))
+		return restart_syscall();
 
 	old = *valp;
 	ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
 	new = *valp;
 
 	if (write && old != new) {
-		struct net *net = ctl->extra2;
-
-		if (!rtnl_net_trylock(net))
-			return restart_syscall();
-
 		if (valp == &net->ipv6.devconf_dflt->proxy_ndp) {
 			inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
 						     NETCONFA_PROXY_NEIGH,
@@ -6514,8 +6513,9 @@ static int addrconf_sysctl_proxy_ndp(const struct ctl_table *ctl, int write,
 						     idev->dev->ifindex,
 						     &idev->cnf);
 		}
-		rtnl_net_unlock(net);
 	}
+	if (write)
+		rtnl_net_unlock(net);
 
 	return ret;
 }
-- 
2.54.0

[PATCH net v3 6/6] ipv6: fix missing notification for ignore_routes_with_linkdown

[Fernando Fernandez Mancera]

When changing the ignore_routes_with_linkdown sysctl for a specific
interface, the RTM_NEWNETCONF netlink notification was not being emitted
to userspace. Fix this by emitting the notification when needed.

In addition, fix bogus return value for successful "all" and specific
interface write operation leading to a wrong reset of the position
pointer.

Fixes: 35103d11173b ("net: ipv6 sysctl option to ignore routes when nexthop link is down")
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/ipv6/addrconf.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 82b6f603faa0..cbe681de3818 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -955,11 +955,7 @@ static int addrconf_fixup_linkdown(const struct ctl_table *table, int *p, int ne
 						     NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
 						     NETCONFA_IFINDEX_DEFAULT,
 						     net->ipv6.devconf_dflt);
-		rtnl_net_unlock(net);
-		return 0;
-	}
-
-	if (p == &net->ipv6.devconf_all->ignore_routes_with_linkdown) {
+	} else if (p == &net->ipv6.devconf_all->ignore_routes_with_linkdown) {
 		WRITE_ONCE(net->ipv6.devconf_dflt->ignore_routes_with_linkdown, newf);
 		addrconf_linkdown_change(net, newf);
 		if ((!newf) ^ (!old))
@@ -968,11 +964,21 @@ static int addrconf_fixup_linkdown(const struct ctl_table *table, int *p, int ne
 						     NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
 						     NETCONFA_IFINDEX_ALL,
 						     net->ipv6.devconf_all);
+	} else {
+		if (!newf ^ !old) {
+			struct inet6_dev *idev = table->extra1;
+
+			inet6_netconf_notify_devconf(net,
+						     RTM_NEWNETCONF,
+						     NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
+						     idev->dev->ifindex,
+						     &idev->cnf);
+		}
 	}
 
 	rtnl_net_unlock(net);
 
-	return 1;
+	return 0;
 }
 
 #endif
-- 
2.54.0

Re: [PATCH net v3 0/6] ipv6: fix error handling in disable_ipv6 sysctl

[Ido Schimmel]

On Mon, Jun 22, 2026 at 03:08:51PM +0200, Fernando Fernandez Mancera wrote:
> While working on a different IPv6 patch series I have spotted multiple
> minor bugs around sysctl error handling and notifications. In general,
> they are not serious issues.

For the series:

Reviewed-by: Ido Schimmel <idosch@nvidia.com>