Hi Jingbo,
Sorry for the late reply.
On 2024/5/6 13:50, Jingbo Xu wrote:
On 5/6/24 11:57 AM, Baokun Li wrote:
On 2024/5/6 11:48, Jingbo Xu wrote:
On 4/24/24 11:39 AM, libao...@huaweicloud.com wrote:
From: Baokun Li <libaok...@huawei.com>
This prevents concurrency from causing access to a freed req.
Could you give more details on how the concurrent access will happen?
How could another process access the &cache->reqs xarray after it has
been flushed?
Similar logic to restore leading to UAF:
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)
// close dev fd
cachefiles_flush_reqs
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 !!!
How could the second cachefiles_ondemand_get_fd() get called here, given
the cache has been flushed and flagged as DEAD?
I was in a bit of a rush to reply earlier, and that graph above is
wrong. Please see the one below:
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
// close dev fd
cachefiles_flush_reqs
complete(&REQ_A->done)
kfree(REQ_A)
xa_lock(&cache->reqs);
cachefiles_ondemand_select_req
req->msg.opcode != CACHEFILES_OP_READ
// req use-after-free !!!
xa_unlock(&cache->reqs);
xa_destroy(&cache->reqs)
Even with CACHEFILES_DEAD set, we can still read the requests, so
accessing it after the request has been freed will trigger use-after-free.
Thanks,
Baokun
---
fs/cachefiles/daemon.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 6465e2574230..ccb7b707ea4b 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -159,6 +159,7 @@ static void cachefiles_flush_reqs(struct
cachefiles_cache *cache)
xa_for_each(xa, index, req) {
req->error = -EIO;
complete(&req->done);
+ __xa_erase(xa, index);
}
xa_unlock(xa);
