In the Linux kernel, the following vulnerability has been resolved: net/smc: stop killed, freed...

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

net/smc: stop killed, freed and out_of_sync sharing a byte

The three connection state flags are single-bit bitfields, so they occupy one byte of struct smc_connection and every store to one is a read-modify-write of the other two:

u8  killed : 1;
u8  freed : 1;
u8  out_of_sync : 1;

They are not written under a common lock. smc_cdc_msg_validate() sets out_of_sync from the receive tasklet, while smc_conn_kill() sets killed from process context under lock_sock(), and the receive path does not defer to the backlog when the socket is owned -- smc_cdc_msg_recv() takes only bh_lock_sock().

Give each flag its own byte so a store no longer touches its neighbours. All readers test them as booleans and are unchanged. struct smc_connection grows by two bytes.