Fix a KMSAN kernel-infoleak detected  by the syzbot .

[net?] KMSAN: kernel-infoleak in __skb_datagram_iter

In tcf_ife_dump(), the variable 'opt' was partially initialized using a
designatied initializer. While the padding bytes are reamined
uninitialized. nla_put() copies the entire structure into a
netlink message, these uninitialized bytes leaked to userspace.

Initialize the structure with memset before assigning its fields
to ensure all members and padding are cleared prior to beign copied.

This change silences the KMSAN report and prevents potential information
leaks from the kernel memory.

This fix has been tested and validated by syzbot. This patch closes the
bug reported at the following syzkaller link and ensures no infoleak.

Reported-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
Tested-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
Fixes: ef6980b6becb ("introduce IFE action")
Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
---
Fix a KMSAN kernel-infoleak detected  by the syzbot .

[net?] KMSAN: kernel-infoleak in __skb_datagram_iter

In tcf_ife_dump(), the variable 'opt' was partially initialized using a
designatied initializer. While the padding bytes are reamined
uninitialized. nla_put() copies the entire structure into a
netlink message, these uninitialized bytes leaked to userspace.

Initialize the structure with memset before assigning its fields
to ensure all members and padding are cleared prior to beign copied.
---
 net/sched/act_ife.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
index 107c6d83dc5c..608ef6cc2224 100644
--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c
@@ -644,13 +644,16 @@ static int tcf_ife_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 	unsigned char *b = skb_tail_pointer(skb);
 	struct tcf_ife_info *ife = to_ife(a);
 	struct tcf_ife_params *p;
-	struct tc_ife opt = {
-		.index = ife->tcf_index,
-		.refcnt = refcount_read(&ife->tcf_refcnt) - ref,
-		.bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
-	};
+	struct tc_ife opt;
 	struct tcf_t t;
 
+	memset(&opt, 0, sizeof(opt));
+	memset(&t, 0, sizeof(t));
+
+	opt.index = ife->tcf_index,
+	opt.refcnt = refcount_read(&ife->tcf_refcnt) - ref,
+	opt.bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
+
 	spin_lock_bh(&ife->tcf_lock);
 	opt.action = ife->tcf_action;
 	p = rcu_dereference_protected(ife->params,

---
base-commit: d127176862a93c4b3216bda533d2bee170af5e71
change-id: 20251031-infoleak-8a7de6afc987

Best regards,
-- 
Ranganath V N <vnranganath.20@gmail.com>

On Fri, Oct 31, 2025 at 5:24 AM Ranganath V N <vnranganath.20@gmail.com> wrote:
>
> Fix a KMSAN kernel-infoleak detected  by the syzbot .
>
> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
>
> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
> designatied initializer. While the padding bytes are reamined
> uninitialized. nla_put() copies the entire structure into a
> netlink message, these uninitialized bytes leaked to userspace.
>
> Initialize the structure with memset before assigning its fields
> to ensure all members and padding are cleared prior to beign copied.
>
> This change silences the KMSAN report and prevents potential information
> leaks from the kernel memory.
>
> This fix has been tested and validated by syzbot. This patch closes the
> bug reported at the following syzkaller link and ensures no infoleak.
>
> Reported-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
> Tested-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
> Fixes: ef6980b6becb ("introduce IFE action")
> Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
> ---
> Fix a KMSAN kernel-infoleak detected  by the syzbot .
>
> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
>
> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
> designatied initializer. While the padding bytes are reamined
> uninitialized. nla_put() copies the entire structure into a
> netlink message, these uninitialized bytes leaked to userspace.
>
> Initialize the structure with memset before assigning its fields
> to ensure all members and padding are cleared prior to beign copied.
> ---
>  net/sched/act_ife.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
> index 107c6d83dc5c..608ef6cc2224 100644
> --- a/net/sched/act_ife.c
> +++ b/net/sched/act_ife.c
> @@ -644,13 +644,16 @@ static int tcf_ife_dump(struct sk_buff *skb, struct tc_action *a, int bind,
>         unsigned char *b = skb_tail_pointer(skb);
>         struct tcf_ife_info *ife = to_ife(a);
>         struct tcf_ife_params *p;
> -       struct tc_ife opt = {
> -               .index = ife->tcf_index,
> -               .refcnt = refcount_read(&ife->tcf_refcnt) - ref,
> -               .bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
> -       };
> +       struct tc_ife opt;
>         struct tcf_t t;
>
> +       memset(&opt, 0, sizeof(opt));
> +       memset(&t, 0, sizeof(t));

Why is the second memset() needed ? Please do not add unrelated changes.

Also I would also fix tcf_connmark_dump()

> +
> +       opt.index = ife->tcf_index,
> +       opt.refcnt = refcount_read(&ife->tcf_refcnt) - ref,
> +       opt.bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
> +
>         spin_lock_bh(&ife->tcf_lock);
>         opt.action = ife->tcf_action;
>         p = rcu_dereference_protected(ife->params,
>
> ---
> base-commit: d127176862a93c4b3216bda533d2bee170af5e71
> change-id: 20251031-infoleak-8a7de6afc987
>
> Best regards,
> --
> Ranganath V N <vnranganath.20@gmail.com>
>

>> Fix a KMSAN kernel-infoleak detected  by the syzbot .
>>
>> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
>>
>> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
>> designatied initializer. While the padding bytes are reamined
>> uninitialized. nla_put() copies the entire structure into a
>> netlink message, these uninitialized bytes leaked to userspace.
>>
>> Initialize the structure with memset before assigning its fields
>> to ensure all members and padding are cleared prior to beign copied.
>>
>> This change silences the KMSAN report and prevents potential information
>> leaks from the kernel memory.
>>
>> This fix has been tested and validated by syzbot. This patch closes the
>> bug reported at the following syzkaller link and ensures no infoleak.
>>
>> Reported-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
>> Tested-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
>> Fixes: ef6980b6becb ("introduce IFE action")
>> Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
>> ---
>> Fix a KMSAN kernel-infoleak detected  by the syzbot .
>>
>> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
>>
>> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
>> designatied initializer. While the padding bytes are reamined
>> uninitialized. nla_put() copies the entire structure into a
>> netlink message, these uninitialized bytes leaked to userspace.
>>
>> Initialize the structure with memset before assigning its fields
>> to ensure all members and padding are cleared prior to beign copied.
>> ---
>>  net/sched/act_ife.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
>> index 107c6d83dc5c..608ef6cc2224 100644
>> --- a/net/sched/act_ife.c
>> +++ b/net/sched/act_ife.c
>> @@ -644,13 +644,16 @@ static int tcf_ife_dump(struct sk_buff *skb, struct tc_action *a, int bind,
>>         unsigned char *b = skb_tail_pointer(skb);
>>         struct tcf_ife_info *ife = to_ife(a);
>>         struct tcf_ife_params *p;
>> -       struct tc_ife opt = {
>> -               .index = ife->tcf_index,
>> -               .refcnt = refcount_read(&ife->tcf_refcnt) - ref,
>> -               .bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
>> -       };
>> +       struct tc_ife opt;
>>         struct tcf_t t;
>>
>> +       memset(&opt, 0, sizeof(opt));
>> +       memset(&t, 0, sizeof(t));
>
>Why is the second memset() needed ? Please do not add unrelated changes.
>
>Also I would also fix tcf_connmark_dump()

Hi Eric,
Do you want me fix tcf_connmark_dump() in this patch or new?

Regards,
Ranganath

On Fri, Oct 31, 2025 at 8:56 AM Ranganath V N <vnranganath.20@gmail.com> wrote:
>
> >> Fix a KMSAN kernel-infoleak detected  by the syzbot .
> >>
> >> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
> >>
> >> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
> >> designatied initializer. While the padding bytes are reamined
> >> uninitialized. nla_put() copies the entire structure into a
> >> netlink message, these uninitialized bytes leaked to userspace.
> >>
> >> Initialize the structure with memset before assigning its fields
> >> to ensure all members and padding are cleared prior to beign copied.
> >>
> >> This change silences the KMSAN report and prevents potential information
> >> leaks from the kernel memory.
> >>
> >> This fix has been tested and validated by syzbot. This patch closes the
> >> bug reported at the following syzkaller link and ensures no infoleak.
> >>
> >> Reported-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
> >> Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
> >> Tested-by: syzbot+0c85cae3350b7d486aee@syzkaller.appspotmail.com
> >> Fixes: ef6980b6becb ("introduce IFE action")
> >> Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
> >> ---
> >> Fix a KMSAN kernel-infoleak detected  by the syzbot .
> >>
> >> [net?] KMSAN: kernel-infoleak in __skb_datagram_iter
> >>
> >> In tcf_ife_dump(), the variable 'opt' was partially initialized using a
> >> designatied initializer. While the padding bytes are reamined
> >> uninitialized. nla_put() copies the entire structure into a
> >> netlink message, these uninitialized bytes leaked to userspace.
> >>
> >> Initialize the structure with memset before assigning its fields
> >> to ensure all members and padding are cleared prior to beign copied.
> >> ---
> >>  net/sched/act_ife.c | 13 ++++++++-----
> >>  1 file changed, 8 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
> >> index 107c6d83dc5c..608ef6cc2224 100644
> >> --- a/net/sched/act_ife.c
> >> +++ b/net/sched/act_ife.c
> >> @@ -644,13 +644,16 @@ static int tcf_ife_dump(struct sk_buff *skb, struct tc_action *a, int bind,
> >>         unsigned char *b = skb_tail_pointer(skb);
> >>         struct tcf_ife_info *ife = to_ife(a);
> >>         struct tcf_ife_params *p;
> >> -       struct tc_ife opt = {
> >> -               .index = ife->tcf_index,
> >> -               .refcnt = refcount_read(&ife->tcf_refcnt) - ref,
> >> -               .bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
> >> -       };
> >> +       struct tc_ife opt;
> >>         struct tcf_t t;
> >>
> >> +       memset(&opt, 0, sizeof(opt));
> >> +       memset(&t, 0, sizeof(t));
> >
> >Why is the second memset() needed ? Please do not add unrelated changes.
> >
> >Also I would also fix tcf_connmark_dump()
>
> Hi Eric,
> Do you want me fix tcf_connmark_dump() in this patch or new?

Send a series of two patches, thank you.

Hi Xin,

Thank you for the feedback and response to the patch.
I would like to know that above analysis is valid or not.
And do you want me to test this suggestion with the syzbot?

regards,
Ranganath