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netlink: Fix wraparounds of sk->sk_rmem_alloc.

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Netlink has this pattern in some places

  if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
  	atomic_add(skb->truesize, &sk->sk_rmem_alloc);

, which has the same problem fixed by commit 5a465a0da1 ("udp:
Fix multiple wraparounds of sk->sk_rmem_alloc.").

For example, if we set INT_MAX to SO_RCVBUFFORCE, the condition
is always false as the two operands are of int.

Then, a single socket can eat as many skb as possible until OOM
happens, and we can see multiple wraparounds of sk->sk_rmem_alloc.

Let's fix it by using atomic_add_return() and comparing the two
variables as unsigned int.

Before:
  [root@fedora ~]# ss -f netlink
  Recv-Q      Send-Q Local Address:Port                Peer Address:Port
  -1668710080 0               rtnl:nl_wraparound/293               *

After:
  [root@fedora ~]# ss -f netlink
  Recv-Q     Send-Q Local Address:Port                Peer Address:Port
  2147483072 0               rtnl:nl_wraparound/290               *
  ^
  `--- INT_MAX - 576

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Reported-by: Jason Baron <jbaron@akamai.com>
Closes: https://lore.kernel.org/netdev/cover.1750285100.git.jbaron@akamai.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250704054824.1580222-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2025-07-04 05:48:18 +00:00 committed by Jakub Kicinski
parent 4e2bba30b1
commit ae8f160e7e
1 changed files with 53 additions and 36 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

89
net/netlink/af_netlink.c
View file

@ -387,7 +387,6 @@ static void netlink_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
WARN_ON(skb->sk != NULL);
skb->sk = sk;
skb->destructor = netlink_skb_destructor;
atomic_add(skb->truesize, &sk->sk_rmem_alloc);
sk_mem_charge(sk, skb->truesize);
}
@ -1212,41 +1211,48 @@ struct sk_buff *netlink_alloc_large_skb(unsigned int size, int broadcast)
int netlink_attachskb(struct sock *sk, struct sk_buff *skb,
long *timeo, struct sock *ssk)
{
DECLARE_WAITQUEUE(wait, current);
struct netlink_sock *nlk;
unsigned int rmem;
nlk = nlk_sk(sk);
rmem = atomic_add_return(skb->truesize, &sk->sk_rmem_alloc);
if ((atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
test_bit(NETLINK_S_CONGESTED, &nlk->state))) {
DECLARE_WAITQUEUE(wait, current);
if (!*timeo) {
if (!ssk || netlink_is_kernel(ssk))
netlink_overrun(sk);
sock_put(sk);
kfree_skb(skb);
return -EAGAIN;
}
__set_current_state(TASK_INTERRUPTIBLE);
add_wait_queue(&nlk->wait, &wait);
if ((atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
test_bit(NETLINK_S_CONGESTED, &nlk->state)) &&
!sock_flag(sk, SOCK_DEAD))
*timeo = schedule_timeout(*timeo);
__set_current_state(TASK_RUNNING);
remove_wait_queue(&nlk->wait, &wait);
sock_put(sk);
if (signal_pending(current)) {
kfree_skb(skb);
return sock_intr_errno(*timeo);
}
return 1;
if ((rmem == skb->truesize || rmem < READ_ONCE(sk->sk_rcvbuf)) &&
!test_bit(NETLINK_S_CONGESTED, &nlk->state)) {
netlink_skb_set_owner_r(skb, sk);
return 0;
}
netlink_skb_set_owner_r(skb, sk);
return 0;
atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
if (!*timeo) {
if (!ssk || netlink_is_kernel(ssk))
netlink_overrun(sk);
sock_put(sk);
kfree_skb(skb);
return -EAGAIN;
}
__set_current_state(TASK_INTERRUPTIBLE);
add_wait_queue(&nlk->wait, &wait);
rmem = atomic_read(&sk->sk_rmem_alloc);
if (((rmem && rmem + skb->truesize > READ_ONCE(sk->sk_rcvbuf)) ||
test_bit(NETLINK_S_CONGESTED, &nlk->state)) &&
!sock_flag(sk, SOCK_DEAD))
*timeo = schedule_timeout(*timeo);
__set_current_state(TASK_RUNNING);
remove_wait_queue(&nlk->wait, &wait);
sock_put(sk);
if (signal_pending(current)) {
kfree_skb(skb);
return sock_intr_errno(*timeo);
}
return 1;
}
static int __netlink_sendskb(struct sock *sk, struct sk_buff *skb)
@ -1307,6 +1313,7 @@ static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb,
ret = -ECONNREFUSED;
if (nlk->netlink_rcv != NULL) {
ret = skb->len;
atomic_add(skb->truesize, &sk->sk_rmem_alloc);
netlink_skb_set_owner_r(skb, sk);
NETLINK_CB(skb).sk = ssk;
netlink_deliver_tap_kernel(sk, ssk, skb);
@ -1383,13 +1390,19 @@ EXPORT_SYMBOL_GPL(netlink_strict_get_check);
static int netlink_broadcast_deliver(struct sock *sk, struct sk_buff *skb)
{
struct netlink_sock *nlk = nlk_sk(sk);
unsigned int rmem, rcvbuf;
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
rmem = atomic_add_return(skb->truesize, &sk->sk_rmem_alloc);
rcvbuf = READ_ONCE(sk->sk_rcvbuf);
if ((rmem != skb->truesize || rmem <= rcvbuf) &&
!test_bit(NETLINK_S_CONGESTED, &nlk->state)) {
netlink_skb_set_owner_r(skb, sk);
__netlink_sendskb(sk, skb);
return atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1);
return rmem > (rcvbuf >> 1);
}
atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
return -1;
}
@ -2249,6 +2262,7 @@ static int netlink_dump(struct sock *sk, bool lock_taken)
struct module *module;
int err = -ENOBUFS;
int alloc_min_size;
unsigned int rmem;
int alloc_size;
if (!lock_taken)
@ -2258,9 +2272,6 @@ static int netlink_dump(struct sock *sk, bool lock_taken)
goto errout_skb;
}
if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
goto errout_skb;
/* NLMSG_GOODSIZE is small to avoid high order allocations being
* required, but it makes sense to _attempt_ a 32KiB allocation
* to reduce number of system calls on dump operations, if user
@ -2283,6 +2294,12 @@ static int netlink_dump(struct sock *sk, bool lock_taken)
if (!skb)
goto errout_skb;
rmem = atomic_add_return(skb->truesize, &sk->sk_rmem_alloc);
if (rmem >= READ_ONCE(sk->sk_rcvbuf)) {
atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
goto errout_skb;
}
/* Trim skb to allocated size. User is expected to provide buffer as
* large as max(min_dump_alloc, 32KiB (max_recvmsg_len capped at
* netlink_recvmsg())). dump will pack as many smaller messages as