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cgroup: fix cgroup_sk_alloc() for sk_clone_lock()

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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
d979a39d72 ("cgroup: duplicate cgroup reference when cloning sockets")
tried to fix it but not compeletely. It seems not easy to trigger until
the recent commit 090e28b229
("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") was merged.

Fixes: bd1060a1d6 ("sock, cgroup: add sock->sk_cgroup")
Reported-by: Cameron Berkenpas <cam@neo-zeon.de>
Reported-by: Peter Geis <pgwipeout@gmail.com>
Reported-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Reported-by: Daniël Sonck <dsonck92@gmail.com>
Reported-by: Zhang Qiang <qiang.zhang@windriver.com>
Tested-by: Cameron Berkenpas <cam@neo-zeon.de>
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cong Wang 2020-07-02 11:52:56 -07:00 committed by David S. Miller
parent aea23c323d
commit ad0f75e5f5
4 changed files with 27 additions and 16 deletions
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6
include/linux/cgroup-defs.h
View File

@ -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;

4
include/linux/cgroup.h
View File

@ -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_ptr(struct sock_cgroup_data *skcd)
*/
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_ptr(struct sock_cgroup_data *skcd)
#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 */

31
kernel/cgroup/cgroup.c
View File

@ -6439,18 +6439,8 @@ 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;
}
@ -6475,10 +6465,27 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
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);
}

2
net/core/sock.c
View File

@ -1926,7 +1926,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
/* 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);