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Message-ID: <20200720164541.GA139672@carbon.dhcp.thefacebook.com>
Date: Mon, 20 Jul 2020 09:46:10 -0700
From: Roman Gushchin <guro@...com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
Cameron Berkenpas <cam@...-zeon.de>,
Peter Geis <pgwipeout@...il.com>,
Lu Fengqi <lufq.fnst@...fujitsu.com>,
Daniël Sonck <dsonck92@...il.com>,
Zhang Qiang <qiang.zhang@...driver.com>,
Thomas Lamprecht <t.lamprecht@...xmox.com>,
Daniel Borkmann <daniel@...earbox.net>,
Zefan Li <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
Cong Wang <xiyou.wangcong@...il.com>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 5.7 021/244] cgroup: fix cgroup_sk_alloc() for
sk_clone_lock()
On Mon, Jul 20, 2020 at 05:34:52PM +0200, Greg Kroah-Hartman wrote:
> From: Cong Wang <xiyou.wangcong@...il.com>
>
> [ Upstream commit ad0f75e5f57ccbceec13274e1e242f2b5a6397ed ]
Hi Greg!
There is a fix for this commit:
14b032b8f8fc ("cgroup: Fix sock_cgroup_data on big-endian.")
Can you, please, grab it too?
Thanks!
>
> 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 <cam@...-zeon.de>
> Reported-by: Peter Geis <pgwipeout@...il.com>
> Reported-by: Lu Fengqi <lufq.fnst@...fujitsu.com>
> Reported-by: Daniël Sonck <dsonck92@...il.com>
> Reported-by: Zhang Qiang <qiang.zhang@...driver.com>
> Tested-by: Cameron Berkenpas <cam@...-zeon.de>
> Tested-by: Peter Geis <pgwipeout@...il.com>
> Tested-by: Thomas Lamprecht <t.lamprecht@...xmox.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Roman Gushchin <guro@...com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> include/linux/cgroup-defs.h | 6 ++++--
> include/linux/cgroup.h | 4 +++-
> kernel/cgroup/cgroup.c | 31 +++++++++++++++++++------------
> net/core/sock.c | 2 +-
> 4 files changed, 27 insertions(+), 16 deletions(-)
>
> --- a/include/linux/cgroup-defs.h
> +++ b/include/linux/cgroup-defs.h
> @@ -790,7 +790,8 @@ struct sock_cgroup_data {
> union {
> #ifdef __LITTLE_ENDIAN
> struct {
> - u8 is_data;
> + u8 is_data : 1;
> + u8 no_refcnt : 1;
> u8 padding;
> u16 prioidx;
> u32 classid;
> @@ -800,7 +801,8 @@ struct sock_cgroup_data {
> u32 classid;
> u16 prioidx;
> u8 padding;
> - u8 is_data;
> + u8 no_refcnt : 1;
> + u8 is_data : 1;
> } __packed;
> #endif
> u64 val;
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -822,6 +822,7 @@ extern spinlock_t cgroup_sk_update_lock;
>
> void cgroup_sk_alloc_disable(void);
> void cgroup_sk_alloc(struct sock_cgroup_data *skcd);
> +void cgroup_sk_clone(struct sock_cgroup_data *skcd);
> void cgroup_sk_free(struct sock_cgroup_data *skcd);
>
> static inline struct cgroup *sock_cgroup_ptr(struct sock_cgroup_data *skcd)
> @@ -835,7 +836,7 @@ static inline struct cgroup *sock_cgroup
> */
> v = READ_ONCE(skcd->val);
>
> - if (v & 1)
> + if (v & 3)
> return &cgrp_dfl_root.cgrp;
>
> return (struct cgroup *)(unsigned long)v ?: &cgrp_dfl_root.cgrp;
> @@ -847,6 +848,7 @@ static inline struct cgroup *sock_cgroup
> #else /* CONFIG_CGROUP_DATA */
>
> static inline void cgroup_sk_alloc(struct sock_cgroup_data *skcd) {}
> +static inline void cgroup_sk_clone(struct sock_cgroup_data *skcd) {}
> static inline void cgroup_sk_free(struct sock_cgroup_data *skcd) {}
>
> #endif /* CONFIG_CGROUP_DATA */
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -6447,18 +6447,8 @@ void cgroup_sk_alloc_disable(void)
>
> void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
> {
> - if (cgroup_sk_alloc_disabled)
> - return;
> -
> - /* Socket clone path */
> - if (skcd->val) {
> - /*
> - * We might be cloning a socket which is left in an empty
> - * cgroup and the cgroup might have already been rmdir'd.
> - * Don't use cgroup_get_live().
> - */
> - cgroup_get(sock_cgroup_ptr(skcd));
> - cgroup_bpf_get(sock_cgroup_ptr(skcd));
> + if (cgroup_sk_alloc_disabled) {
> + skcd->no_refcnt = 1;
> return;
> }
>
> @@ -6483,10 +6473,27 @@ void cgroup_sk_alloc(struct sock_cgroup_
> rcu_read_unlock();
> }
>
> +void cgroup_sk_clone(struct sock_cgroup_data *skcd)
> +{
> + if (skcd->val) {
> + if (skcd->no_refcnt)
> + return;
> + /*
> + * We might be cloning a socket which is left in an empty
> + * cgroup and the cgroup might have already been rmdir'd.
> + * Don't use cgroup_get_live().
> + */
> + cgroup_get(sock_cgroup_ptr(skcd));
> + cgroup_bpf_get(sock_cgroup_ptr(skcd));
> + }
> +}
> +
> void cgroup_sk_free(struct sock_cgroup_data *skcd)
> {
> struct cgroup *cgrp = sock_cgroup_ptr(skcd);
>
> + if (skcd->no_refcnt)
> + return;
> cgroup_bpf_put(cgrp);
> cgroup_put(cgrp);
> }
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1837,7 +1837,7 @@ struct sock *sk_clone_lock(const struct
> /* sk->sk_memcg will be populated at accept() time */
> newsk->sk_memcg = NULL;
>
> - cgroup_sk_alloc(&newsk->sk_cgrp_data);
> + cgroup_sk_clone(&newsk->sk_cgrp_data);
>
> rcu_read_lock();
> filter = rcu_dereference(sk->sk_filter);
>
>
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