On Tue, 2022-05-03 at 14:17 -0700, Eric Dumazet wrote:

On Tue, May 3, 2022 at 4:40 AM [off-list ref] wrote:

quoted

Hello:

This patch was applied to netdev/net.git (master)
by Paolo Abeni [off-list ref]:

On Mon, 2 May 2022 10:40:18 +0900 you wrote:

quoted

syzbot is reporting use-after-free read in tcp_retransmit_timer() [1],
for TCP socket used by RDS is accessing sock_net() without acquiring a
refcount on net namespace. Since TCP's retransmission can happen after
a process which created net namespace terminated, we need to explicitly
acquire a refcount.

Link: https://syzkaller.appspot.com/bug?extid=694120e1002c117747ed [1]
Reported-by: syzbot <redacted>
Fixes: 26abe14379f8e2fa ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
Fixes: 8a68173691f03661 ("net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <redacted>

[...]

Here is the summary with links:
  - [v2] net: rds: acquire refcount on TCP sockets
    https://git.kernel.org/netdev/net/c/3a58f13a881e

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

I think we merged this patch too soon.

My fault.

My question is : What prevents rds_tcp_conn_path_connect(), and thus
rds_tcp_tune() to be called
after the netns refcount already reached 0 ?

I guess we can wait for next syzbot report, but I think that get_net()
should be replaced
by maybe_get_net()

Should we revert this patch before the next pull request, if a suitable
incremental fix is not available by then?

It looks like the window of opportunity for the race is roughly the
same?

Thanks!

Paolo