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ksmbd: Fix race condition in RPC handle list access 

The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd
session. Access to this list is intended to be protected by
'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was
flawed, leading to potential race conditions.

In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock
before calling xa_store() and xa_erase(). Since these operations modify
the XArray structure, a write lock is required to ensure exclusive access
and prevent data corruption from concurrent modifications.

Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load()
without holding any lock at all. This could lead to reading inconsistent
data or a potential use-after-free if an entry is concurrently removed and
the pointer is dereferenced.

Fix these issues by:
1. Using down_write() and up_write() in ksmbd_session_rpc_open()
   to ensure exclusive access during XArray modification, and ensuring
   the lock is correctly released on error paths.
2. Adding down_read() and up_read() in ksmbd_session_rpc_method()
   to safely protect the lookup.

Fixes: a1f46c99d9 ("ksmbd: fix use-after-free in ksmbd_session_rpc_open")
Fixes: b685757c7b ("ksmbd: Implements sess->rpc_handle_list as xarray")
Cc: stable@vger.kernel.org
Signed-off-by: Yunseong Kim <ysk@kzalloc.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Yunseong Kim 2025-09-15 22:44:09 +00:00 committed by Steve French
parent a9401710a5
commit 305853cce3
1 changed files with 17 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
fs/smb/server/mgmt/user_session.c
View File

@ -104,29 +104,32 @@ int ksmbd_session_rpc_open(struct ksmbd_session *sess, char *rpc_name)
if (!entry)
return -ENOMEM;
down_read(&sess->rpc_lock);
entry->method = method;
entry->id = id = ksmbd_ipc_id_alloc();
if (id < 0)
goto free_entry;
down_write(&sess->rpc_lock);
old = xa_store(&sess->rpc_handle_list, id, entry, KSMBD_DEFAULT_GFP);
if (xa_is_err(old))
if (xa_is_err(old)) {
up_write(&sess->rpc_lock);
goto free_id;
}
resp = ksmbd_rpc_open(sess, id);
if (!resp)
goto erase_xa;
if (!resp) {
xa_erase(&sess->rpc_handle_list, entry->id);
up_write(&sess->rpc_lock);
goto free_id;
}
up_read(&sess->rpc_lock);
up_write(&sess->rpc_lock);
kvfree(resp);
return id;
erase_xa:
xa_erase(&sess->rpc_handle_list, entry->id);
free_id:
ksmbd_rpc_id_free(entry->id);
free_entry:
kfree(entry);
up_read(&sess->rpc_lock);
return -EINVAL;
}
@ -144,9 +147,14 @@ void ksmbd_session_rpc_close(struct ksmbd_session *sess, int id)
int ksmbd_session_rpc_method(struct ksmbd_session *sess, int id)
{
struct ksmbd_session_rpc *entry;
int method;
down_read(&sess->rpc_lock);
entry = xa_load(&sess->rpc_handle_list, id);
return entry ? entry->method : 0;
method = entry ? entry->method : 0;
up_read(&sess->rpc_lock);
return method;
}
void ksmbd_session_destroy(struct ksmbd_session *sess)