rxrpc: Fix data-race warning and potential load/store tearing

Overview

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix data-race warning and potential load/store tearing

Fix the following:

    BUG: KCSAN: data-race in rxrpc_peer_keepalive_worker / rxrpc_send_data_packet

which is reporting an issue with the reads and writes to ->last_tx_at in:

    conn->peer->last_tx_at = ktime_get_seconds();

and:

    keepalive_at = peer->last_tx_at + RXRPC_KEEPALIVE_TIME;

The lockless accesses to these to values aren't actually a problem as the read only needs an approximate time of last transmission for the purposes of deciding whether or not the transmission of a keepalive packet is warranted yet.

Also, as ->last_tx_at is a 64-bit value, tearing can occur on a 32-bit arch.

Fix both of these by switching to an unsigned int for ->last_tx_at and only storing the LSW of the time64_t. It can then be reconstructed at need provided no more than 68 years has elapsed since the last transmission.

Affected

• Linux >= ace45bec6d77bc061c3c3d8ad99e298ea9800c2b < 49b8ef1abfe7713e15d9128006cb76e413b12b57
• Linux >= ace45bec6d77bc061c3c3d8ad99e298ea9800c2b < a426f29ac3fa3465093567ab763ada46762fb57c
• Linux >= ace45bec6d77bc061c3c3d8ad99e298ea9800c2b < c08cf314191cd0f8699089715efb9eff030f0086
• Linux >= ace45bec6d77bc061c3c3d8ad99e298ea9800c2b < f8cf1368e0a5491b27189a695c36f64e48f3d19d
• Linux >= ace45bec6d77bc061c3c3d8ad99e298ea9800c2b < 5d5fe8bcd331f1e34e0943ec7c18432edfcf0e8b
• Linux 4.17

Remediation

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