Hi Jia,
On 2024/4/24 22:55, Jia Zhu wrote:
在 2024/4/24 11:39, libaokun@xxxxxxxxxxxxxxx 写道:
From: Baokun Li <libaokun1@xxxxxxxxxx>
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.
Hi Baokun,
Thank you for catching this issue. Shall we fix this by following steps:
cachefiles_ondemand_fd_release()
xas_for_each(req)
if req is not CACHEFILES_OP_READ
flush
cachefiles_ondemand_restore()
xas_for_each(req)
if req is not CACHEFILES_REQ_NEW && op is (OPEN or CLOSE)
reset req to CACHEFILES_REQ_NEW
By implementing these steps:
1. In real daemon failover case： only pending read reqs will be
reserved. cachefiles_ondemand_select_req will reopen the object by
processing READ req.
2. In daemon alive case： Only read reqs will be reset to
CACHEFILES_REQ_NEW.
This way, in the fialover case, some processes that are being mounted
will fail, which is contrary to our intention of making the user senseless.
In my opinion, it's better to keep making users senseless.
Thanks,
Baokun
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 <houtao1@xxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/cachefiles/internal.h | 1 +
fs/cachefiles/ondemand.c | 44 ++++++++++++++++++++++------------------
2 files changed, 25 insertions(+), 20 deletions(-)
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index d33169f0018b..7745b8abc3aa 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -138,6 +138,7 @@ static inline bool
cachefiles_in_ondemand_mode(struct cachefiles_cache *cache)
struct cachefiles_req {
struct cachefiles_object *object;
struct completion done;
+ refcount_t ref;
int error;
struct cachefiles_msg msg;
};
diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index fd49728d8bae..56d12fe4bf73 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -4,6 +4,12 @@
#include <linux/uio.h>
#include "internal.h"
+static inline void cachefiles_req_put(struct cachefiles_req *req)
+{
+ if (refcount_dec_and_test(&req->ref))
+ kfree(req);
+}
+
static int cachefiles_ondemand_fd_release(struct inode *inode,
struct file *file)
{
@@ -299,7 +305,6 @@ ssize_t cachefiles_ondemand_daemon_read(struct
cachefiles_cache *cache,
{
struct cachefiles_req *req;
struct cachefiles_msg *msg;
- unsigned long id = 0;
size_t n;
int ret = 0;
XA_STATE(xas, &cache->reqs, cache->req_id_next);
@@ -330,41 +335,39 @@ ssize_t cachefiles_ondemand_daemon_read(struct
cachefiles_cache *cache,
xas_clear_mark(&xas, CACHEFILES_REQ_NEW);
cache->req_id_next = xas.xa_index + 1;
+ refcount_inc(&req->ref);
xa_unlock(&cache->reqs);
- id = xas.xa_index;
-
if (msg->opcode == CACHEFILES_OP_OPEN) {
ret = cachefiles_ondemand_get_fd(req);
if (ret) {
cachefiles_ondemand_set_object_close(req->object);
- goto error;
+ goto out;
}
}
- msg->msg_id = id;
+ msg->msg_id = xas.xa_index;
msg->object_id = req->object->ondemand->ondemand_id;
if (copy_to_user(_buffer, msg, n) != 0) {
ret = -EFAULT;
if (msg->opcode == CACHEFILES_OP_OPEN)
close_fd(((struct cachefiles_open *)msg->data)->fd);
- goto error;
}
-
- /* CLOSE request has no reply */
- if (msg->opcode == CACHEFILES_OP_CLOSE) {
- xa_erase(&cache->reqs, id);
- complete(&req->done);
+out:
+ /* Remove error request and CLOSE request has no reply */
+ if (ret || msg->opcode == CACHEFILES_OP_CLOSE) {
+ xas_reset(&xas);
+ xas_lock(&xas);
+ if (xas_load(&xas) == req) {
+ req->error = ret;
+ complete(&req->done);
+ xas_store(&xas, NULL);
+ }
+ xas_unlock(&xas);
}
-
- return n;
-
-error:
- xa_erase(&cache->reqs, id);
- req->error = ret;
- complete(&req->done);
- return ret;
+ cachefiles_req_put(req);
+ return ret ? ret : n;
}
typedef int (*init_req_fn)(struct cachefiles_req *req, void
*private);
@@ -394,6 +397,7 @@ static int cachefiles_ondemand_send_req(struct
cachefiles_object *object,
goto out;
}
+ refcount_set(&req->ref, 1);
req->object = object;
init_completion(&req->done);
req->msg.opcode = opcode;
@@ -455,7 +459,7 @@ static int cachefiles_ondemand_send_req(struct
cachefiles_object *object,
wake_up_all(&cache->daemon_pollwq);
wait_for_completion(&req->done);
ret = req->error;
- kfree(req);
+ cachefiles_req_put(req);
return ret;
out:
/* Reset the object to close state in error handling path.
