Re: [PATCH v2 5/8] net: af_can: do not leave a dangling sk pointer in can_create()

On Tue, Oct 8, 2024 at 3:38 AM Vincent MAILHOL
[off-list ref] wrote:

Hi Ignat,

Thanks for the patch.

On Tue. 8 Oct. 2024 at 06:37, Ignat Korchagin [off-list ref] wrote:

quoted

On error can_create() frees the allocated sk object, but sock_init_data()
has already attached it to the provided sock object. This will leave a
dangling sk pointer in the sock object and may cause use-after-free later.

I was about to suggest that this should be backported to stable, but
after reading the cover letter, I now understand that this patch is
more an improvement to avoid false positives on kmemleak & Cie. Maybe
the description could be a bit more nuanced? After patch 1/8 of this
series, it seems that the use-after-free is not possible anymore.

If we go with Kuniyuki's suggestion in the cover email to replace the
explicit NULL with DEBUG_NET_WARN_ON_ONCE(sock->sk) in __sock_create()
then use-after-free would be possible again except we will easily
catch it. But I will review the description, when I respin the patches
to net-next as requested by Jakub.

quoted

Signed-off-by: Ignat Korchagin <redacted>

See above comment as notwithstanding. This said:

Reviewed-by: Vincent Mailhol <redacted>

Thank you.

quoted

---
 net/can/af_can.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 707576eeeb58..01f3fbb3b67d 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c

@@ -171,6 +171,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
                /* release sk on errors */
                sock_orphan(sk);
                sock_put(sk);
+               sock->sk = NULL;
        }

  errout:
--

2.39.5