netlink: Fix wraparounds of sk->sk_rmem_alloc.

Overview

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

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 9da025150b7c14a8390fc06aea314c0a4011e82c
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c4ceaac5c5ba0b992ee1dc88e2a02421549e5c98
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < fd69af06101090eaa60b3d216ae715f9c0a58e5b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 76602d8e13864524382b0687dc32cd8f19164d5a
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 55baecb9eb90238f60a8350660d6762046ebd3bd
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 4b8e18af7bea92f8b7fb92d40aeae729209db250
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < cd7ff61bfffd7000143c42bbffb85eeb792466d6
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ae8f160e7eb24240a2a79fc4c815c6a0d4ee16cc
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.