From: Eric W. Biederman ebiederm@xmission.com
commit f9d87929d451d3e649699d0f1d74f71f77ad38f5 upstream.
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@quicinc.com Reported-by: Mathias Krause minipli@grsecurity.net Tested-by: Mathias Krause minipli@grsecurity.net Reviewed-by: Mathias Krause minipli@grsecurity.net Reviewed-by: Alexey Gladkov legion@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@vger.kernel.org Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/ucount.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -190,6 +190,7 @@ struct ucounts *alloc_ucounts(struct use kfree(new); } else { hlist_add_head(&new->node, hashent); + get_user_ns(new->ns); spin_unlock_irq(&ucounts_lock); return new; } @@ -210,6 +211,7 @@ 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); } }