[PATCH] ksmbd: ipc: fix use-after-free in ipc_msg_send_request

[Qianchang Zhao <pioooooooooip@gmail.com>]

ipc_msg_send_request() waits for a generic netlink reply using an
ipc_msg_table_entry on the stack. The generic netlink handler
(handle_generic_event()/handle_response()) fills entry->response under
ipc_msg_table_lock, but ipc_msg_send_request() used to validate and free
entry->response without holding the same lock.

Under high concurrency this allows a race where handle_response() is
copying data into entry->response while ipc_msg_send_request() has just
freed it, leading to a slab-use-after-free reported by KASAN in
handle_generic_event():

  BUG: KASAN: slab-use-after-free in handle_generic_event+0x3c4/0x5f0 [ksmbd]
  Write of size 12 at addr ffff888198ee6e20 by task pool/109349
  ...
  Freed by task:
    kvfree
    ipc_msg_send_request [ksmbd]
    ksmbd_rpc_open -> ksmbd_session_rpc_open [ksmbd]

Fix by:
- Taking ipc_msg_table_lock in ipc_msg_send_request() while validating
  entry->response, freeing it when invalid, and removing the entry from
  ipc_msg_table.
- Returning the final entry->response pointer to the caller only after
  the hash entry is removed under the lock.
- Returning NULL in the error path, preserving the original API
  semantics.

This makes all accesses to entry->response consistent with
handle_response(), which already updates and fills the response buffer
under ipc_msg_table_lock, and closes the race that allowed the UAF.

Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
---
 fs/smb/server/transport_ipc.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index 46f87fd1c..7b1a060da 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -532,6 +532,7 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry)
 static void *ipc_msg_send_request(struct ksmbd_ipc_msg *msg, unsigned int handle)
 {
 	struct ipc_msg_table_entry entry;
+	void *response = NULL;
 	int ret;
 
 	if ((int)handle < 0)
@@ -553,6 +554,8 @@ static void *ipc_msg_send_request(struct ksmbd_ipc_msg *msg, unsigned int handle
 	ret = wait_event_interruptible_timeout(entry.wait,
 					       entry.response != NULL,
 					       IPC_WAIT_TIMEOUT);
+
+	down_write(&ipc_msg_table_lock);
 	if (entry.response) {
 		ret = ipc_validate_msg(&entry);
 		if (ret) {
@@ -560,11 +563,19 @@ static void *ipc_msg_send_request(struct ksmbd_ipc_msg *msg, unsigned int handle
 			entry.response = NULL;
 		}
 	}
+
+	response = entry.response;
+	hash_del(&entry.ipc_table_hlist);
+	up_write(&ipc_msg_table_lock);
+
+	return response;
+
 out:
 	down_write(&ipc_msg_table_lock);
 	hash_del(&entry.ipc_table_hlist);
 	up_write(&ipc_msg_table_lock);
-	return entry.response;
+
+	return NULL;
 }
 
 static int ksmbd_ipc_heartbeat_request(void)
-- 
2.34.1