netlink: Fix wraparounds of sk->sk_rmem_alloc.

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: netlink: Fix wraparounds of sk->sk_rmem_alloc. 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 5a465a0da13e ("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

References

• https://git.kernel.org/stable/c/9da025150b7c14a8390fc06aea314c0a4011e82c
• https://git.kernel.org/stable/c/c4ceaac5c5ba0b992ee1dc88e2a02421549e5c98
• https://git.kernel.org/stable/c/fd69af06101090eaa60b3d216ae715f9c0a58e5b
• https://git.kernel.org/stable/c/76602d8e13864524382b0687dc32cd8f19164d5a
• https://git.kernel.org/stable/c/55baecb9eb90238f60a8350660d6762046ebd3bd
• https://git.kernel.org/stable/c/4b8e18af7bea92f8b7fb92d40aeae729209db250
• https://git.kernel.org/stable/c/cd7ff61bfffd7000143c42bbffb85eeb792466d6
• https://git.kernel.org/stable/c/ae8f160e7eb24240a2a79fc4c815c6a0d4ee16cc