[PATCH net] net/smc: protect clcsock lifetime in smc_getname

[Chengfeng Ye <nicoyip.dev@gmail.com>]

smc_getname() dereferences smc->clcsock without holding
clcsock_release_lock. Link-group termination can release the CLC socket
through smc_close_active_abort() while the SMC socket is still open,
for example after shutdown(SHUT_WR).

A getsockname() caller can load smc->clcsock, then the termination worker
can clear the pointer and call sock_release() before the caller accesses
clcsock->ops or invokes getname(). This causes a use-after-free; if the
worker clears the pointer before the load, it causes a NULL dereference.
The syscall's file reference keeps the SMC socket alive but does not
prevent asynchronous release of its CLC socket.

KASAN reported:

  BUG: KASAN: slab-use-after-free in smc_getname+0x19e/0x1b0
  Read of size 8 at addr ffff888109abb4e0 by task poc/103
  Call Trace:
   smc_getname+0x19e/0x1b0
   do_getsockname+0xe5/0x170
   __sys_getsockname+0x8c/0x100

  Allocated by task 95:
   sock_alloc_inode+0x1e/0x280
   sock_alloc+0x3d/0x240
   __sock_create+0x7e/0x430
   smc_create+0x121/0x240

  Freed by task 0:
   kmem_cache_free+0xcc/0x340
   rcu_core+0x50a/0x1850

  Last potentially related work creation:
   evict+0x446/0x6c0
   smc_clcsock_release+0xa8/0xd0
   smc_close_active_abort+0x26a/0x3a0
   __smc_lgr_terminate.part.0+0x137/0x2e0

Hold clcsock_release_lock across the pointer check and the getname()
callback, as the socket option handlers already do. Return -EBADF if
the CLC socket has already been released, preserving the existing peer
state check and the callback's return value otherwise.

Fixes: b03faa1fafc8 ("net/smc: postpone release of clcsock")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/smc/af_smc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index e9f93b3ab435..8b3ee70f8433 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -2784,6 +2784,7 @@ int smc_getname(struct socket *sock, struct sockaddr *addr,
 		int peer)
 {
 	struct smc_sock *smc;
+	int rc = -EBADF;
 
 	if (peer && (sock->sk->sk_state != SMC_ACTIVE) &&
 	    (sock->sk->sk_state != SMC_APPCLOSEWAIT1))
@@ -2791,7 +2792,11 @@ int smc_getname(struct socket *sock, struct sockaddr *addr,
 
 	smc = smc_sk(sock->sk);
 
-	return smc->clcsock->ops->getname(smc->clcsock, addr, peer);
+	mutex_lock(&smc->clcsock_release_lock);
+	if (smc->clcsock)
+		rc = smc->clcsock->ops->getname(smc->clcsock, addr, peer);
+	mutex_unlock(&smc->clcsock_release_lock);
+	return rc;
 }
 
 int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
-- 
2.43.0