Re: [PATCH 5.15] net: defer final 'struct net' free in netns dismantle

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 0f6ede9fbc747e2553612271bce108f7517e7a45

WARNING: Author mismatch between patch and upstream commit:
Backport author: Vasiliy Kovalev<kovalev@altlinux.org>
Commit author: Eric Dumazet<edumazet@google.com>


Status in newer kernel trees:
6.12.y | Present (different SHA1: 6610c7f8a8d4)
6.6.y | Present (different SHA1: b7a79e51297f)
6.1.y | Present (different SHA1: 3267b254dc0a)
5.15.y | Not found

Note: The patch differs from the upstream commit:
---
1:  0f6ede9fbc74 ! 1:  bb5ecf836b36 net: defer final 'struct net' free in netns dismantle
    @@ Metadata
      ## Commit message ##
         net: defer final 'struct net' free in netns dismantle
     
    +    commit 0f6ede9fbc747e2553612271bce108f7517e7a45 upstream.
    +
         Ilya reported a slab-use-after-free in dst_destroy [1]
     
         Issue is in xfrm6_net_init() and xfrm4_net_init() :
    @@ Commit message
         Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
         Link: https://patch.msgid.link/20241204125455.3871859-1-edumazet@google.com
         Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    +    Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
     
      ## include/net/net_namespace.h ##
     @@ include/net/net_namespace.h: struct net {
    @@ net/core/net_namespace.c: static struct net *net_alloc(void)
      static void net_free(struct net *net)
      {
      	if (refcount_dec_and_test(&net->passive)) {
    -@@ net/core/net_namespace.c: static void net_free(struct net *net)
    - 		/* There should not be any trackers left there. */
    - 		ref_tracker_dir_exit(&net->notrefcnt_tracker);
    - 
    + 		kfree(rcu_access_pointer(net->gen));
     -		kmem_cache_free(net_cachep, net);
    ++
     +		/* Wait for an extra rcu_barrier() before final free. */
     +		llist_add(&net->defer_free_list, &defer_free_list);
      	}
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.15.y       |  Success    |  Success   |