On Thu, Dec 11, 2025 at 7:54 PM Vitaly Chikunov [off-list ref] wrote:

On Sun, Nov 09, 2025 at 02:43:36PM +0530, Ranganath V N wrote:

quoted

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 <redacted>
---
 net/sched/act_ife.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
index 107c6d83dc5c..7c6975632fc2 100644
--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c

@@ -644,13 +644,15 @@ 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));
+
+     opt.index = ife->tcf_index,
+     opt.refcnt = refcount_read(&ife->tcf_refcnt) - ref,
+     opt.bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,

Are you sure this is correct to delimit with commas instead of
semicolons?

This already causes build failures of 5.10.247-rt141 kernel, because
their spin_lock_bh unrolls into do { .. } while (0):

Do you have access to this?
commit 205305c028ad986d0649b8b100bab6032dcd1bb5
Author: Chen Ni [off-list ref]
Date:   Wed Nov 12 15:27:09 2025 +0800

    net/sched: act_ife: convert comma to semicolon

cheers,
jamal

     CC [M]  net/sched/act_ife.o
   In file included from ./include/linux/spinlock.h:329,
                    from ./include/linux/mmzone.h:8,
                    from ./include/linux/gfp.h:6,
                    from ./include/linux/mm.h:10,
                    from ./include/linux/bvec.h:14,
                    from ./include/linux/skbuff.h:17,
                    from net/sched/act_ife.c:20:
   net/sched/act_ife.c: In function 'tcf_ife_dump':
   ./include/linux/spinlock_rt.h:44:2: error: expected expression before 'do'
      44 |  do {     \
         |  ^~
   net/sched/act_ife.c:655:2: note: in expansion of macro 'spin_lock_bh'
     655 |  spin_lock_bh(&ife->tcf_lock);
         |  ^~~~~~~~~~~~
   make[2]: *** [scripts/Makefile.build:286: net/sched/act_ife.o] Error 1
   make[2]: *** Waiting for unfinished jobs....


Thanks,

quoted

+
      spin_lock_bh(&ife->tcf_lock);
      opt.action = ife->tcf_action;
      p = rcu_dereference_protected(ife->params,
--
2.43.0