diff options
| author | Yunseong Kim <yskelg@gmail.com> | 2024-11-25 16:45:55 +0900 |
|---|---|---|
| committer | Steve French <stfrench@microsoft.com> | 2024-11-25 18:58:27 -0600 |
| commit | 9a8c5d89d327ff58e9b2517f8a6afb4181d32c6e (patch) | |
| tree | 211250a62a32e734ad337de662ea543b5b6aa9ca /fs/smb | |
| parent | db5f8243067f87138888a6842acbce5340d1626c (diff) | |
ksmbd: fix use-after-free in SMB request handling
A race condition exists between SMB request handling in
`ksmbd_conn_handler_loop()` and the freeing of `ksmbd_conn` in the
workqueue handler `handle_ksmbd_work()`. This leads to a UAF.
- KASAN: slab-use-after-free Read in handle_ksmbd_work
- KASAN: slab-use-after-free in rtlock_slowlock_locked
This race condition arises as follows:
- `ksmbd_conn_handler_loop()` waits for `conn->r_count` to reach zero:
`wait_event(conn->r_count_q, atomic_read(&conn->r_count) == 0);`
- Meanwhile, `handle_ksmbd_work()` decrements `conn->r_count` using
`atomic_dec_return(&conn->r_count)`, and if it reaches zero, calls
`ksmbd_conn_free()`, which frees `conn`.
- However, after `handle_ksmbd_work()` decrements `conn->r_count`,
it may still access `conn->r_count_q` in the following line:
`waitqueue_active(&conn->r_count_q)` or `wake_up(&conn->r_count_q)`
This results in a UAF, as `conn` has already been freed.
The discovery of this UAF can be referenced in the following PR for
syzkaller's support for SMB requests.
Link: https://github.com/google/syzkaller/pull/5524
Fixes: ee426bfb9d09 ("ksmbd: add refcnt to ksmbd_conn struct")
Cc: linux-cifs@vger.kernel.org
Cc: stable@vger.kernel.org # v6.6.55+, v6.10.14+, v6.11.3+
Cc: syzkaller@googlegroups.com
Signed-off-by: Yunseong Kim <yskelg@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Diffstat (limited to 'fs/smb')
| -rw-r--r-- | fs/smb/server/server.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/fs/smb/server/server.c b/fs/smb/server/server.c index b3dceefe6c5f..930d7566b52e 100644 --- a/fs/smb/server/server.c +++ b/fs/smb/server/server.c @@ -276,8 +276,12 @@ static void handle_ksmbd_work(struct work_struct *wk) * disconnection. waitqueue_active is safe because it * uses atomic operation for condition. */ + atomic_inc(&conn->refcnt); if (!atomic_dec_return(&conn->r_count) && waitqueue_active(&conn->r_count_q)) wake_up(&conn->r_count_q); + + if (atomic_dec_and_test(&conn->refcnt)) + kfree(conn); } /** |