APPLIED [OEM-5.14] Re: [SRU OEM-5.14/Jammy] ucount: Make get_ucount a safe get_user replacement

[Timo Aaltonen]

On 31.1.2022 13.06, Thadeu Lima de Souza Cascardo wrote:
> From: "Eric W. Biederman" <ebiederm at xmission.com>
> 
> When the ucount code was refactored to create get_ucount it was missed
> that some of the contexts in which a rlimit is kept elevated can be
> the only reference to the user/ucount in the system.
> 
> Ordinary ucount references exist in places that also have a reference
> to the user namspace, but in POSIX message queues, the SysV shm code,
> and the SIGPENDING code there is no independent user namespace
> reference.
> 
> Inspection of the the user_namespace show no instance of circular
> references between struct ucounts and the user_namespace.  So
> hold a reference from struct ucount to i's user_namespace to
> resolve this problem.
> 
> Link: https://lore.kernel.org/lkml/YZV7Z+yXbsx9p3JN@fixkernel.com/
> Reported-by: Qian Cai <quic_qiancai at quicinc.com>
> Reported-by: Mathias Krause <minipli at grsecurity.net>
> Tested-by: Mathias Krause <minipli at grsecurity.net>
> Reviewed-by: Mathias Krause <minipli at grsecurity.net>
> Reviewed-by: Alexey Gladkov <legion at kernel.org>
> Fixes: d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of ucounts")
> Fixes: 6e52a9f0532f ("Reimplement RLIMIT_MSGQUEUE on top of ucounts")
> Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
> Cc: stable at vger.kernel.org
> Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
> (cherry picked from commit f9d87929d451d3e649699d0f1d74f71f77ad38f5)
> CVE-2022-24122
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> ---
>   kernel/ucount.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 16feb710ee63..804f64799fc1 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -184,6 +184,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
>   			kfree(new);
>   		} else {
>   			hlist_add_head(&new->node, hashent);
> +			get_user_ns(new->ns);
>   			spin_unlock_irq(&ucounts_lock);
>   			return new;
>   		}
> @@ -204,6 +205,7 @@ void put_ucounts(struct ucounts *ucounts)
>   	if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
>   		hlist_del_init(&ucounts->node);
>   		spin_unlock_irqrestore(&ucounts_lock, flags);
> +		put_user_ns(ucounts->ns);
>   		kfree(ucounts);
>   	}
>   }

applied to oem-5.14, thanks

-- 
t