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 <[email protected]>
---
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..e9f16e5e3515 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_flag = 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_flag) {
if (nla_len(attr) < sizeof(flags))
return -EINVAL;
- have_flags = true;
+ br_flag = 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_flag)
+ memcpy(nla_data(br_flag), &flags, sizeof(flags));
out:
return err;
}
--
2.17.1
On 2/27/24 13:01, 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 <[email protected]>
> ---
That fix is obviously broken, I don't know how I missed it back then.
One comment below,
> 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..e9f16e5e3515 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_flag = NULL;
Please name the variable to something that describes it better, like
br_flags_attr.
> 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_flag) {
> if (nla_len(attr) < sizeof(flags))
> return -EINVAL;
>
> - have_flags = true;
> + br_flag = 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_flag)
> + memcpy(nla_data(br_flag), &flags, sizeof(flags));
> out:
> return err;
> }
Hello Nikolay,
>
> That fix is obviously broken, I don't know how I missed it back then.
> One comment below,
Guess is because this loop is so weird :(
I looked into the kernel and did not find other codes that refer to the
NLA pointer outside the `nla_for_each_nested` loop.
> ...
> > 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_flag = NULL;
>
> Please name the variable to something that describes it better, like
> br_flags_attr.
>
OK, I will rename the variable and send another version.
> > 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) {