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net/smc: Transitional solution for clcsock race issue
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We encountered a crash in smc_setsockopt() and it is caused by
accessing smc->clcsock after clcsock was released.

 BUG: kernel NULL pointer dereference, address: 0000000000000020
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] PREEMPT SMP PTI
 CPU: 1 PID: 50309 Comm: nginx Kdump: loaded Tainted: G E     5.16.0-rc4+ #53
 RIP: 0010:smc_setsockopt+0x59/0x280 [smc]
 Call Trace:
  <TASK>
  __sys_setsockopt+0xfc/0x190
  __x64_sys_setsockopt+0x20/0x30
  do_syscall_64+0x34/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae
 RIP: 0033:0x7f16ba83918e
  </TASK>

This patch tries to fix it by holding clcsock_release_lock and
checking whether clcsock has already been released before access.

In case that a crash of the same reason happens in smc_getsockopt()
or smc_switch_to_fallback(), this patch also checkes smc->clcsock
in them too. And the caller of smc_switch_to_fallback() will identify
whether fallback succeeds according to the return value.

Fixes: fd57770 ("net/smc: wait for pending work before clcsock release_sock")
Link: https://lore.kernel.org/lkml/5dd7ffd1-28e2-24cc-9442-1defec27375e@linux.ibm.com/T/
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@davem330
Wen Gu authored and davem330 committed Jan 24, 2022
1 parent 3a5d9db commit c0bf3d8
Showing 1 changed file with 51 additions and 12 deletions.
63 changes: 51 additions & 12 deletions net/smc/af_smc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -566,12 +566,17 @@ static void smc_stat_fallback(struct smc_sock *smc)
mutex_unlock(&net->smc.mutex_fback_rsn);
}

static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
static int smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
{
wait_queue_head_t *smc_wait = sk_sleep(&smc->sk);
wait_queue_head_t *clc_wait = sk_sleep(smc->clcsock->sk);
wait_queue_head_t *clc_wait;
unsigned long flags;

mutex_lock(&smc->clcsock_release_lock);
if (!smc->clcsock) {
mutex_unlock(&smc->clcsock_release_lock);
return -EBADF;
}
smc->use_fallback = true;
smc->fallback_rsn = reason_code;
smc_stat_fallback(smc);
Expand All @@ -586,18 +591,30 @@ static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
* smc socket->wq, which should be removed
* to clcsocket->wq during the fallback.
*/
clc_wait = sk_sleep(smc->clcsock->sk);
spin_lock_irqsave(&smc_wait->lock, flags);
spin_lock_nested(&clc_wait->lock, SINGLE_DEPTH_NESTING);
list_splice_init(&smc_wait->head, &clc_wait->head);
spin_unlock(&clc_wait->lock);
spin_unlock_irqrestore(&smc_wait->lock, flags);
}
mutex_unlock(&smc->clcsock_release_lock);
return 0;
}

/* fall back during connect */
static int smc_connect_fallback(struct smc_sock *smc, int reason_code)
{
smc_switch_to_fallback(smc, reason_code);
struct net *net = sock_net(&smc->sk);
int rc = 0;

rc = smc_switch_to_fallback(smc, reason_code);
if (rc) { /* fallback fails */
this_cpu_inc(net->smc.smc_stats->clnt_hshake_err_cnt);
if (smc->sk.sk_state == SMC_INIT)
sock_put(&smc->sk); /* passive closing */
return rc;
}
smc_copy_sock_settings_to_clc(smc);
smc->connect_nonblock = 0;
if (smc->sk.sk_state == SMC_INIT)
Expand Down Expand Up @@ -1518,11 +1535,12 @@ static void smc_listen_decline(struct smc_sock *new_smc, int reason_code,
{
/* RDMA setup failed, switch back to TCP */
smc_conn_abort(new_smc, local_first);
if (reason_code < 0) { /* error, no fallback possible */
if (reason_code < 0 ||
smc_switch_to_fallback(new_smc, reason_code)) {
/* error, no fallback possible */
smc_listen_out_err(new_smc);
return;
}
smc_switch_to_fallback(new_smc, reason_code);
if (reason_code && reason_code != SMC_CLC_DECL_PEERDECL) {
if (smc_clc_send_decline(new_smc, reason_code, version) < 0) {
smc_listen_out_err(new_smc);
Expand Down Expand Up @@ -1964,8 +1982,11 @@ static void smc_listen_work(struct work_struct *work)

/* check if peer is smc capable */
if (!tcp_sk(newclcsock->sk)->syn_smc) {
smc_switch_to_fallback(new_smc, SMC_CLC_DECL_PEERNOSMC);
smc_listen_out_connected(new_smc);
rc = smc_switch_to_fallback(new_smc, SMC_CLC_DECL_PEERNOSMC);
if (rc)
smc_listen_out_err(new_smc);
else
smc_listen_out_connected(new_smc);
return;
}

Expand Down Expand Up @@ -2254,7 +2275,9 @@ static int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)

if (msg->msg_flags & MSG_FASTOPEN) {
if (sk->sk_state == SMC_INIT && !smc->connect_nonblock) {
smc_switch_to_fallback(smc, SMC_CLC_DECL_OPTUNSUPP);
rc = smc_switch_to_fallback(smc, SMC_CLC_DECL_OPTUNSUPP);
if (rc)
goto out;
} else {
rc = -EINVAL;
goto out;
Expand Down Expand Up @@ -2447,6 +2470,11 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
/* generic setsockopts reaching us here always apply to the
* CLC socket
*/
mutex_lock(&smc->clcsock_release_lock);
if (!smc->clcsock) {
mutex_unlock(&smc->clcsock_release_lock);
return -EBADF;
}
if (unlikely(!smc->clcsock->ops->setsockopt))
rc = -EOPNOTSUPP;
else
Expand All @@ -2456,6 +2484,7 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
sk->sk_err = smc->clcsock->sk->sk_err;
sk_error_report(sk);
}
mutex_unlock(&smc->clcsock_release_lock);

if (optlen < sizeof(int))
return -EINVAL;
Expand All @@ -2472,7 +2501,7 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
case TCP_FASTOPEN_NO_COOKIE:
/* option not supported by SMC */
if (sk->sk_state == SMC_INIT && !smc->connect_nonblock) {
smc_switch_to_fallback(smc, SMC_CLC_DECL_OPTUNSUPP);
rc = smc_switch_to_fallback(smc, SMC_CLC_DECL_OPTUNSUPP);
} else {
rc = -EINVAL;
}
Expand Down Expand Up @@ -2515,13 +2544,23 @@ static int smc_getsockopt(struct socket *sock, int level, int optname,
char __user *optval, int __user *optlen)
{
struct smc_sock *smc;
int rc;

smc = smc_sk(sock->sk);
mutex_lock(&smc->clcsock_release_lock);
if (!smc->clcsock) {
mutex_unlock(&smc->clcsock_release_lock);
return -EBADF;
}
/* socket options apply to the CLC socket */
if (unlikely(!smc->clcsock->ops->getsockopt))
if (unlikely(!smc->clcsock->ops->getsockopt)) {
mutex_unlock(&smc->clcsock_release_lock);
return -EOPNOTSUPP;
return smc->clcsock->ops->getsockopt(smc->clcsock, level, optname,
optval, optlen);
}
rc = smc->clcsock->ops->getsockopt(smc->clcsock, level, optname,
optval, optlen);
mutex_unlock(&smc->clcsock_release_lock);
return rc;
}

static int smc_ioctl(struct socket *sock, unsigned int cmd,
Expand Down

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