[PATCH v2 04/12] cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()

libaokun
2024-05-15T08:56:40Z

From: Baokun Li <libaokun1@huawei.com>

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+0xb41/0xb60
Read of size 8 at addr ffff888122e84088 by task ondemand-04-dae/963

CPU: 13 PID: 963 Comm: ondemand-04-dae Not tainted 6.8.0-dirty #564
Call Trace:
kasan_report+0x93/0xc0
cachefiles_ondemand_daemon_read+0xb41/0xb60
vfs_read+0x169/0xb50
ksys_read+0xf5/0x1e0

Allocated by task 116:
kmem_cache_alloc+0x140/0x3a0
cachefiles_lookup_cookie+0x140/0xcd0
fscache_cookie_state_machine+0x43c/0x1230
[...]

Freed by task 792:
kmem_cache_free+0xfe/0x390
cachefiles_put_object+0x241/0x480
fscache_cookie_state_machine+0x5c8/0x1230
[...]
==================================================================

Following is the process that triggers the issue:

mount | daemon_thread1 | daemon_thread2
------------------------------------------------------------
cachefiles_withdraw_cookie
cachefiles_ondemand_clean_object(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
msg->object_id = req->object->ondemand->ondemand_id
------ 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
copy_to_user(_buffer, msg, n)
xa_erase(&cache->reqs, id)
complete(&REQ_A->done)
------ close(fd) ------
cachefiles_ondemand_fd_release
cachefiles_put_object
cachefiles_put_object
kmem_cache_free(cachefiles_object_jar, object)
REQ_A->object->ondemand->ondemand_id
// object UAF !!!

When we see the request within xa_lock, req->object must not have been
freed yet, so grab the reference count of object before xa_unlock to
avoid the above issue.

Fixes: 0a7e54c1959c ("cachefiles: resend an open request if the read request's object is closed")
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jia Zhu <zhujia.zj@bytedance.com>
---
fs/cachefiles/ondemand.c | 2 ++
include/trace/events/cachefiles.h | 6 +++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 56d12fe4bf73..bb94ef6a6f61 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -336,6 +336,7 @@ 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);
+ cachefiles_grab_object(req->object, cachefiles_obj_get_read_req);
xa_unlock(&cache->reqs);

if (msg->opcode == CACHEFILES_OP_OPEN) {
@@ -355,6 +356,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
close_fd(((struct cachefiles_open *)msg->data)->fd);
}
out:
+ cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
/* Remove error request and CLOSE request has no reply */
if (ret || msg->opcode == CACHEFILES_OP_CLOSE) {
xas_reset(&xas);
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index cf4b98b9a9ed..119a823fb5a0 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -33,6 +33,8 @@ enum cachefiles_obj_ref_trace {
cachefiles_obj_see_withdrawal,
cachefiles_obj_get_ondemand_fd,
cachefiles_obj_put_ondemand_fd,
+ cachefiles_obj_get_read_req,
+ cachefiles_obj_put_read_req,
};

enum fscache_why_object_killed {
@@ -127,7 +129,9 @@ enum cachefiles_error_trace {
EM(cachefiles_obj_see_lookup_cookie, "SEE lookup_cookie") \
EM(cachefiles_obj_see_lookup_failed, "SEE lookup_failed") \
EM(cachefiles_obj_see_withdraw_cookie, "SEE withdraw_cookie") \
- E_(cachefiles_obj_see_withdrawal, "SEE withdrawal")
+ EM(cachefiles_obj_see_withdrawal, "SEE withdrawal") \
+ EM(cachefiles_obj_get_read_req, "GET read_req") \
+ E_(cachefiles_obj_put_read_req, "PUT read_req")

#define cachefiles_coherency_traces \
EM(cachefiles_coherency_check_aux, "BAD aux ") \
--
2.39.2