CVE-2021-46925

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

net/smc: fix kernel panic caused by race of smc_sock

A crash occurs when smc_cdc_tx_handler() tries to access smc_sock

but smc_release() has already freed it.

[ 4570.695099] BUG: unable to handle page fault for address: 000000002eae9e88

[ 4570.696048] #PF: supervisor write access in kernel mode

[ 4570.696728] #PF: error_code(0x0002) - not-present page

[ 4570.697401] PGD 0 P4D 0

[ 4570.697716] Oops: 0002 [#1] PREEMPT SMP NOPTI

[ 4570.698228] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.16.0-rc4+ #111

[ 4570.699013] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 8c24b4c 04/0

[ 4570.699933] RIP: 0010:_raw_spin_lock+0x1a/0x30

<...>

[ 4570.711446] Call Trace:

[ 4570.711746] <IRQ>

[ 4570.711992] smc_cdc_tx_handler+0x41/0xc0

[ 4570.712470] smc_wr_tx_tasklet_fn+0x213/0x560

[ 4570.712981] ? smc_cdc_tx_dismisser+0x10/0x10

[ 4570.713489] tasklet_action_common.isra.17+0x66/0x140

[ 4570.714083] __do_softirq+0x123/0x2f4

[ 4570.714521] irq_exit_rcu+0xc4/0xf0

[ 4570.714934] common_interrupt+0xba/0xe0

Though smc_cdc_tx_handler() checked the existence of smc connection,

smc_release() may have already dismissed and released the smc socket

before smc_cdc_tx_handler() further visits it.

smc_cdc_tx_handler() |smc_release()

if (!conn) |

|

|smc_cdc_tx_dismiss_slots()

| smc_cdc_tx_dismisser()

|

|sock_put(&smc->sk) <- last sock_put,

| smc_sock freed

bh_lock_sock(&smc->sk) (panic) |

To make sure we won't receive any CDC messages after we free the

smc_sock, add a refcount on the smc_connection for inflight CDC

message(posted to the QP but haven't received related CQE), and

don't release the smc_connection until all the inflight CDC messages

haven been done, for both success or failed ones.

Using refcount on CDC messages brings another problem: when the link

is going to be destroyed, smcr_link_clear() will reset the QP, which

then remove all the pending CQEs related to the QP in the CQ. To make

sure all the CQEs will always come back so the refcount on the

smc_connection can always reach 0, smc_ib_modify_qp_reset() was replaced

by smc_ib_modify_qp_error().

And remove the timeout in smc_wr_tx_wait_no_pending_sends() since we

need to wait for all pending WQEs done, or we may encounter use-after-

free when handling CQEs.

For IB device removal routine, we need to wait for all the QPs on that

device been destroyed before we can destroy CQs on the device, or

the refcount on smc_connection won't reach 0 and smc_sock cannot be

released.