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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [PATCH v2 03/12] cachefiles: fix slab-use-after-free in cachefiles_ondemand_get_fd() Content-Language: en-US To: Jingbo Xu , netfs@lists.linux.dev, dhowells@redhat.com, jlayton@kernel.org Cc: hsiangkao@linux.alibaba.com, zhujia.zj@bytedance.com, linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, yangerkun@huawei.com, houtao1@huawei.com, yukuai3@huawei.com, wozizhi@huawei.com, Baokun Li , libaokun@huaweicloud.com References: <20240515084601.3240503-1-libaokun@huaweicloud.com> <20240515084601.3240503-4-libaokun@huaweicloud.com> <7d24fa89-0995-4104-84f1-dac6c8bf4477@linux.alibaba.com> From: Baokun Li In-Reply-To: <7d24fa89-0995-4104-84f1-dac6c8bf4477@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID:cCh0CgAX6RF8E0tmgwizNA--.16021S3 X-Coremail-Antispam: 1UD129KBjvJXoWxZF1UAFyruw43CryUuw43GFg_yoWrJFWxpF ZIya4IyFy8WrW8Crs7ZF15Jr1rJ3y8AFnrWr10qFyIyr4qkr1Fvr17tr1FqF98Cr9FkF4q q3WDuF9rX34qy3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUU9214x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jrv_JF1lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxcIEc7CjxVA2Y2ka 0xkIwI1lc7I2V7IY0VAS07AlzVAYIcxG8wCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7x kEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E 67AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCw CI42IY6xIIjxv20xvEc7CjxVAFwI0_Cr0_Gr1UMIIF0xvE42xK8VAvwI8IcIk0rVW3JVWr Jr1lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8Jr0_Cr1UYx BIdaVFxhVjvjDU0xZFpf9x0JUp6wZUUUUU= X-CM-SenderInfo: 5olet0hnxqqx5xdzvxpfor3voofrz/ On 2024/5/20 16:06, Jingbo Xu wrote: > > On 5/15/24 4:45 PM, libaokun@huaweicloud.com wrote: >> From: Baokun Li >> >> We got the following issue in a fuzz test of randomly issuing the restore >> command: >> >> ================================================================== >> BUG: KASAN: slab-use-after-free in cachefiles_ondemand_daemon_read+0x609/0xab0 >> Write of size 4 at addr ffff888109164a80 by task ondemand-04-dae/4962 >> >> CPU: 11 PID: 4962 Comm: ondemand-04-dae Not tainted 6.8.0-rc7-dirty #542 >> Call Trace: >> kasan_report+0x94/0xc0 >> cachefiles_ondemand_daemon_read+0x609/0xab0 >> vfs_read+0x169/0xb50 >> ksys_read+0xf5/0x1e0 >> >> Allocated by task 626: >> __kmalloc+0x1df/0x4b0 >> cachefiles_ondemand_send_req+0x24d/0x690 >> cachefiles_create_tmpfile+0x249/0xb30 >> cachefiles_create_file+0x6f/0x140 >> cachefiles_look_up_object+0x29c/0xa60 >> cachefiles_lookup_cookie+0x37d/0xca0 >> fscache_cookie_state_machine+0x43c/0x1230 >> [...] >> >> Freed by task 626: >> kfree+0xf1/0x2c0 >> cachefiles_ondemand_send_req+0x568/0x690 >> cachefiles_create_tmpfile+0x249/0xb30 >> cachefiles_create_file+0x6f/0x140 >> cachefiles_look_up_object+0x29c/0xa60 >> cachefiles_lookup_cookie+0x37d/0xca0 >> fscache_cookie_state_machine+0x43c/0x1230 >> [...] >> ================================================================== >> >> Following is the process that triggers the issue: >> >> mount | daemon_thread1 | daemon_thread2 >> ------------------------------------------------------------ >> 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 >> copy_to_user(_buffer, msg, n) >> process_open_req(REQ_A) >> ------ restore ------ >> cachefiles_ondemand_restore >> xas_for_each(&xas, req, ULONG_MAX) >> xas_set_mark(&xas, CACHEFILES_REQ_NEW); >> >> cachefiles_daemon_read >> cachefiles_ondemand_daemon_read >> REQ_A = cachefiles_ondemand_select_req >> >> write(devfd, ("copen %u,%llu", msg->msg_id, size)); >> cachefiles_ondemand_copen >> xa_erase(&cache->reqs, id) >> complete(&REQ_A->done) >> kfree(REQ_A) >> cachefiles_ondemand_get_fd(REQ_A) >> fd = get_unused_fd_flags >> file = anon_inode_getfile >> fd_install(fd, file) >> load = (void *)REQ_A->msg.data; >> load->fd = fd; >> // load UAF !!! >> >> This issue is caused by issuing a restore command when the daemon is still >> alive, which results in a request being processed multiple times thus >> triggering a UAF. So to avoid this problem, add an additional reference >> count to cachefiles_req, which is held while waiting and reading, and then >> released when the waiting and reading is over. >> >> Note that since there is only one reference count for waiting, we need to >> avoid the same request being completed multiple times, so we can only >> complete the request if it is successfully removed from the xarray. >> >> Fixes: e73fa11a356c ("cachefiles: add restore command to recover inflight ondemand read requests") >> Suggested-by: Hou Tao >> Signed-off-by: Baokun Li >> Reviewed-by: Jia Zhu > How could we protect it from being erased from the xarray with the same > message id in this case? We will hold xa_lock while erasing the id to avoid concurrency. -- With Best Regards, Baokun Li