[PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[Lin Ma]

In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
in the function `rtnl_bridge_setlink` to enable the loop to also check
the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
removed the `break` statement and led to an error logic of the flags
writing back at the end of this function.

if (have_flags)
    memcpy(nla_data(attr), &flags, sizeof(flags));
    // attr should point to IFLA_BRIDGE_FLAGS NLA !!!

Before the mentioned commit, the `attr` is granted to be IFLA_BRIDGE_FLAGS.
However, this is not necessarily true fow now as the updated loop will let
the attr point to the last NLA, even an invalid NLA which could cause
overflow writes.

This patch introduces a new variable `br_flag` to save the NLA pointer
that points to IFLA_BRIDGE_FLAGS and uses it to resolve the mentioned
error logic.

Fixes: d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
---
v1 -> v2: rename the br_flag to br_flags_attr which offers better
          description suggested by Nikolay.

 net/core/rtnetlink.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9c4f427f3a50..ae86f751efc3 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -5169,10 +5169,9 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	struct net *net = sock_net(skb->sk);
 	struct ifinfomsg *ifm;
 	struct net_device *dev;
-	struct nlattr *br_spec, *attr = NULL;
+	struct nlattr *br_spec, *attr, *br_flags_attr = NULL;
 	int rem, err = -EOPNOTSUPP;
 	u16 flags = 0;
-	bool have_flags = false;
 
 	if (nlmsg_len(nlh) < sizeof(*ifm))
 		return -EINVAL;
@@ -5190,11 +5189,11 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	br_spec = nlmsg_find_attr(nlh, sizeof(struct ifinfomsg), IFLA_AF_SPEC);
 	if (br_spec) {
 		nla_for_each_nested(attr, br_spec, rem) {
-			if (nla_type(attr) == IFLA_BRIDGE_FLAGS && !have_flags) {
+			if (nla_type(attr) == IFLA_BRIDGE_FLAGS && !br_flags_attr) {
 				if (nla_len(attr) < sizeof(flags))
 					return -EINVAL;
 
-				have_flags = true;
+				br_flags_attr = attr;
 				flags = nla_get_u16(attr);
 			}
 
@@ -5238,8 +5237,8 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		}
 	}
 
-	if (have_flags)
-		memcpy(nla_data(attr), &flags, sizeof(flags));
+	if (br_flags_attr)
+		memcpy(nla_data(br_flags_attr), &flags, sizeof(flags));
 out:
 	return err;
 }
-- 
2.17.1

Re: [PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[Jiri Pirko]

Tue, Feb 27, 2024 at 01:11:28PM CET, linma@zju.edu.cn wrote:
>In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
>IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
>in the function `rtnl_bridge_setlink` to enable the loop to also check
>the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
>removed the `break` statement and led to an error logic of the flags
>writing back at the end of this function.
>
>if (have_flags)
>    memcpy(nla_data(attr), &flags, sizeof(flags));
>    // attr should point to IFLA_BRIDGE_FLAGS NLA !!!
>
>Before the mentioned commit, the `attr` is granted to be IFLA_BRIDGE_FLAGS.
>However, this is not necessarily true fow now as the updated loop will let
>the attr point to the last NLA, even an invalid NLA which could cause
>overflow writes.
>
>This patch introduces a new variable `br_flag` to save the NLA pointer
>that points to IFLA_BRIDGE_FLAGS and uses it to resolve the mentioned
>error logic.
>
>Fixes: d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length")
>Signed-off-by: Lin Ma <linma@zju.edu.cn>
>---
>v1 -> v2: rename the br_flag to br_flags_attr which offers better
>          description suggested by Nikolay.

https://www.kernel.org/doc/html/v6.6/process/maintainer-netdev.html?highlight=network#tl-dr

"don't repost your patches within one 24h period"

Re: [PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[Lin Ma]

> 
> https://www.kernel.org/doc/html/v6.6/process/maintainer-netdev.html?highlight=network#tl-dr
> 
> "don't repost your patches within one 24h period"

Apologize for this mistake, and I promise to be more careful
in the future. Thank you for bringing this to my attention

Regards
Lin

Re: [PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[Nikolay Aleksandrov]

On 2/27/24 14:11, Lin Ma wrote:
> In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
> IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
> in the function `rtnl_bridge_setlink` to enable the loop to also check
> the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
> removed the `break` statement and led to an error logic of the flags
> writing back at the end of this function.
> 
> if (have_flags)
>      memcpy(nla_data(attr), &flags, sizeof(flags));
>      // attr should point to IFLA_BRIDGE_FLAGS NLA !!!
> 
> Before the mentioned commit, the `attr` is granted to be IFLA_BRIDGE_FLAGS.
> However, this is not necessarily true fow now as the updated loop will let
> the attr point to the last NLA, even an invalid NLA which could cause
> overflow writes.
> 
> This patch introduces a new variable `br_flag` to save the NLA pointer
> that points to IFLA_BRIDGE_FLAGS and uses it to resolve the mentioned
> error logic.
> 
> Fixes: d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length")
> Signed-off-by: Lin Ma <linma@zju.edu.cn>
> ---
> v1 -> v2: rename the br_flag to br_flags_attr which offers better
>            description suggested by Nikolay.
> 
>   net/core/rtnetlink.c | 11 +++++------
>   1 file changed, 5 insertions(+), 6 deletions(-)
> 

As Jiri pointed out, you should wait a day before posting another
version. The patch itself looks good to me:

Acked-by: Nikolay Aleksandrov <razor@blackwall.org>

Re: [PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 27 Feb 2024 20:11:28 +0800 you wrote:
> In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
> IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
> in the function `rtnl_bridge_setlink` to enable the loop to also check
> the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
> removed the `break` statement and led to an error logic of the flags
> writing back at the end of this function.
> 
> [...]

Here is the summary with links:
  - [net,v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back
    https://git.kernel.org/netdev/net/c/743ad091fb46

You are awesome, thank you!
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