This is a note to let you know that I've just added the patch titled
cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cachefiles-fix-slab-use-after-free-in-cachefiles_ond.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 5f938b16c5aadb76f041facf14eb623ac63031d2
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date: Wed May 22 19:43:00 2024 +0800
cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()
[ Upstream commit da4a827416066191aafeeccee50a8836a826ba10 ]
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@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240522114308.2402121-5-libaokun@xxxxxxxxxxxxxxx
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Stable-dep-of: 4b4391e77a6b ("cachefiles: defer exposing anon_fd until after copy_to_user() succeeds")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index f8d0a01795702..fd73811c7ce4f 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -369,6 +369,7 @@ 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);
id = xas.xa_index;
@@ -389,6 +390,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
goto err_put_fd;
}
+ cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
/* CLOSE request has no reply */
if (msg->opcode == CACHEFILES_OP_CLOSE) {
xa_erase(&cache->reqs, id);
@@ -402,6 +404,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
if (msg->opcode == CACHEFILES_OP_OPEN)
close_fd(((struct cachefiles_open *)msg->data)->fd);
error:
+ cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
xas_reset(&xas);
xas_lock(&xas);
if (xas_load(&xas) == req) {
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index e3213af847cdf..7d931db02b934 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 {
@@ -129,7 +131,9 @@ enum cachefiles_error_trace {
EM(cachefiles_obj_see_withdraw_cookie, "SEE withdraw_cookie") \
EM(cachefiles_obj_see_withdrawal, "SEE withdrawal") \
EM(cachefiles_obj_get_ondemand_fd, "GET ondemand_fd") \
- E_(cachefiles_obj_put_ondemand_fd, "PUT ondemand_fd")
+ EM(cachefiles_obj_put_ondemand_fd, "PUT ondemand_fd") \
+ 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 ") \
