cgroup: fix cgroup_sk_alloc() for sk_clone_lock()

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@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>

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5266115..4f1cd0e 100644 (file)
--- 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;

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 4598e4d..618838c 100644 (file)
--- 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_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 */

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 1ea181a..dd24774 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -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);
 }

diff --git a/net/core/sock.c b/net/core/sock.c
index d832c65..2e5b787 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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);