CVE-2019-3837: RHEL6: memory leak in tcp_recvmsg() with NET_DMA

[Vladis Dronov <vdronov () redhat com>]

Heololo,

It was found that the net_dma code in tcp_recvmsg() in the RHEL6 kernel is
thread-unsafe. So an unprivileged multi-threaded userspace application
calling recvmsg() for the same network socket in parallel executed on
ioatdma-enabled hardware with net_dma enabled can leak the memory,
crash the host leading to a denial-of-service, or cause a random memory
corruption.

This flaw was assigned an id of CVE-2019-3837.

net_dma was disabled in the upstream Linux kernel since v3.13-rc5 by
the 77873803363c "net_dma: mark broken" and then completely removed
by the 7bced397510a "net_dma: simple removal".

So this flaw affects RHEL-6 only and any (LTS) Linux kernel (of any
distribution) which has not backported the net_dma disabling commits
mentioned above.

Best regards,
Vladis Dronov | Red Hat, Inc. | Product Security | Senior Software Engineer