From: Cong Wang <[email protected]>
Date: Thu, 2 Jul 2020 11:52:56 -0700
> When we clone a socket in sk_clone_lock(), its sk_cgrp_data is
> copied, so the cgroup refcnt must be taken too. And, unlike the
> sk_alloc() path, sock_update_netprioidx() is not called here.
> Therefore, it is safe and necessary to grab the cgroup refcnt
> even when cgroup_sk_alloc is disabled.
>
> sk_clone_lock() is in BH context anyway, the in_interrupt()
> would terminate this function if called there. And for sk_alloc()
> skcd->val is always zero. So it's safe to factor out the code
> to make it more readable.
>
> The global variable 'cgroup_sk_alloc_disabled' is used to determine
> whether to take these reference counts. It is impossible to make
> the reference counting correct unless we save this bit of information
> in skcd->val. So, add a new bit there to record whether the socket
> has already taken the reference counts. This obviously relies on
> kmalloc() to align cgroup pointers to at least 4 bytes,
> ARCH_KMALLOC_MINALIGN is certainly larger than that.
>
> This bug seems to be introduced since the beginning, commit
> d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets")
> tried to fix it but not compeletely. It seems not easy to trigger until
> the recent commit 090e28b229af
> ("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") was merged.
>
> Fixes: bd1060a1d671 ("sock, cgroup: add sock->sk_cgroup")
> Reported-by: Cameron Berkenpas <[email protected]>
> Reported-by: Peter Geis <[email protected]>
> Reported-by: Lu Fengqi <[email protected]>
> Reported-by: Daniël Sonck <[email protected]>
> Reported-by: Zhang Qiang <[email protected]>
> Tested-by: Cameron Berkenpas <[email protected]>
> Tested-by: Peter Geis <[email protected]>
> Tested-by: Thomas Lamprecht <[email protected]>
> Cc: Daniel Borkmann <[email protected]>
> Cc: Zefan Li <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: Roman Gushchin <[email protected]>
> Signed-off-by: Cong Wang <[email protected]>
Applied and queued up for -stable, thanks!
