On 2024/5/20 16:43, Jingbo Xu wrote:
On 5/15/24 4:45 PM, libaokun@xxxxxxxxxxxxxxx wrote:From: Baokun Li <libaokun1@xxxxxxxxxx> Now every time the daemon reads an open request, it gets a new anonymous fd and ondemand_id. With the introduction of "restore", it is possible to read the same open request more than once, and therefore an object can have more than one anonymous fd. If the anonymous fd is not unique, the following concurrencies will result in an fd leak: t1 | t2 | t3 ------------------------------------------------------------ cachefiles_ondemand_init_object cachefiles_ondemand_send_req REQ_A = kzalloc(sizeof(*req) + data_len) wait_for_completion(&REQ_A->done) cachefiles_daemon_read cachefiles_ondemand_daemon_read REQ_A = cachefiles_ondemand_select_req cachefiles_ondemand_get_fd load->fd = fd0 ondemand_id = object_id0 ------ restore ------ cachefiles_ondemand_restore // restore REQ_A cachefiles_daemon_read cachefiles_ondemand_daemon_read REQ_A = cachefiles_ondemand_select_req cachefiles_ondemand_get_fd load->fd = fd1 ondemand_id = object_id1 process_open_req(REQ_A) write(devfd, ("copen %u,%llu", msg->msg_id, size)) cachefiles_ondemand_copen xa_erase(&cache->reqs, id) complete(&REQ_A->done) kfree(REQ_A) process_open_req(REQ_A) // copen fails due to no req // daemon close(fd1) cachefiles_ondemand_fd_release // set object closed -- umount -- cachefiles_withdraw_cookie cachefiles_ondemand_clean_object cachefiles_ondemand_init_close_req if (!cachefiles_ondemand_object_is_open(object)) return -ENOENT; // The fd0 is not closed until the daemon exits. However, the anonymous fd holds the reference count of the object and the object holds the reference count of the cookie. So even though the cookie has been relinquished, it will not be unhashed and freed until the daemon exits. In fscache_hash_cookie(), when the same cookie is found in the hash list, if the cookie is set with the FSCACHE_COOKIE_RELINQUISHED bit, then the new cookie waits for the old cookie to be unhashed, while the old cookie is waiting for the leaked fd to be closed, if the daemon does not exit in time it will trigger a hung task. To avoid this, allocate a new anonymous fd only if no anonymous fd has been allocated (ondemand_id == 0) or if the previously allocated anonymous fd has been closed (ondemand_id == -1). Moreover, returns an error if ondemand_id is valid, letting the daemon know that the current userland restore logic is abnormal and needs to be checked. Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie") Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>The LOCs of this fix is quite under control. But still it seems that the worst consequence is that the (potential) malicious daemon gets hung. No more effect to the system or other processes. Or does a non-malicious daemon have any chance having the same issue?
If we enable hung_task_panic, it may cause panic to crash the server.
--- fs/cachefiles/ondemand.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-) diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c index d04ddc6576e3..d2d4e27fca6f 100644 --- a/fs/cachefiles/ondemand.c +++ b/fs/cachefiles/ondemand.c @@ -14,11 +14,18 @@ static int cachefiles_ondemand_fd_release(struct inode *inode, struct file *file) { struct cachefiles_object *object = file->private_data; - struct cachefiles_cache *cache = object->volume->cache; - struct cachefiles_ondemand_info *info = object->ondemand; + struct cachefiles_cache *cache; + struct cachefiles_ondemand_info *info; int object_id; struct cachefiles_req *req; - XA_STATE(xas, &cache->reqs, 0); + XA_STATE(xas, NULL, 0); + + if (!object) + return 0; + + info = object->ondemand; + cache = object->volume->cache; + xas.xa = &cache->reqs;xa_lock(&cache->reqs);spin_lock(&info->lock); @@ -288,22 +295,39 @@ static int cachefiles_ondemand_get_fd(struct cachefiles_req *req) goto err_put_fd; }+ spin_lock(&object->ondemand->lock);+ if (object->ondemand->ondemand_id > 0) { + spin_unlock(&object->ondemand->lock); + /* Pair with check in cachefiles_ondemand_fd_release(). */ + file->private_data = NULL; + ret = -EEXIST; + goto err_put_file; + } + file->f_mode |= FMODE_PWRITE | FMODE_LSEEK; fd_install(fd, file);load = (void *)req->msg.data;load->fd = fd; object->ondemand->ondemand_id = object_id; + spin_unlock(&object->ondemand->lock);cachefiles_get_unbind_pincount(cache);trace_cachefiles_ondemand_open(object, &req->msg, load); return 0;+err_put_file:+ fput(file); err_put_fd: put_unused_fd(fd); err_free_id: xa_erase(&cache->ondemand_ids, object_id); err: + spin_lock(&object->ondemand->lock); + /* Avoid marking an opened object as closed. */ + if (object->ondemand->ondemand_id <= 0) + cachefiles_ondemand_set_object_close(object); + spin_unlock(&object->ondemand->lock); cachefiles_put_object(object, cachefiles_obj_put_ondemand_fd); return ret; } @@ -386,10 +410,8 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,if (msg->opcode == CACHEFILES_OP_OPEN) {ret = cachefiles_ondemand_get_fd(req); - if (ret) { - cachefiles_ondemand_set_object_close(req->object); + if (ret) goto out; - } }msg->msg_id = xas.xa_index;
-- With Best Regards, Baokun Li
