[PATCH 4.19 015/105] 9p/fd: fix issue of list_del corruption in p9_fd_cancel()

Greg Kroah-Hartman
2022-12-05T19:18:19Z

From: Zhengchao Shao <shaozhengchao@huawei.com>

[ Upstream commit 11c10956515b8ec44cf4f2a7b9d8bf8b9dc05ec4 ]

Syz reported the following issue:
kernel BUG at lib/list_debug.c:53!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:__list_del_entry_valid.cold+0x5c/0x72
Call Trace:
<TASK>
p9_fd_cancel+0xb1/0x270
p9_client_rpc+0x8ea/0xba0
p9_client_create+0x9c0/0xed0
v9fs_session_init+0x1e0/0x1620
v9fs_mount+0xba/0xb80
legacy_get_tree+0x103/0x200
vfs_get_tree+0x89/0x2d0
path_mount+0x4c0/0x1ac0
__x64_sys_mount+0x33b/0x430
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
</TASK>

The process is as follows:
Thread A: Thread B:
p9_poll_workfn() p9_client_create()
... ...
p9_conn_cancel() p9_fd_cancel()
list_del() ...
... list_del() //list_del
corruption
There is no lock protection when deleting list in p9_conn_cancel(). After
deleting list in Thread A, thread B will delete the same list again. It
will cause issue of list_del corruption.

Setting req->status to REQ_STATUS_ERROR under lock prevents other
cleanup paths from trying to manipulate req_list.
The other thread can safely check req->status because it still holds a
reference to req at this point.

Link: https://lkml.kernel.org/r/20221110122606.383352-1-shaozhengchao@huawei.com
Fixes: 52f1c45dde91 ("9p: trans_fd/p9_conn_cancel: drop client lock earlier")
Reported-by: syzbot+9b69b8d10ab4a7d88056@syzkaller.appspotmail.com
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
[Dominique: add description of the fix in commit message]
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/trans_fd.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 7194ffa58d3e..6aba06a8261c 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -215,9 +215,11 @@ static void p9_conn_cancel(struct p9_conn *m, int err)

list_for_each_entry_safe(req, rtmp, &m->req_list, req_list) {
list_move(&req->req_list, &cancel_list);
+ req->status = REQ_STATUS_ERROR;
}
list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
list_move(&req->req_list, &cancel_list);
+ req->status = REQ_STATUS_ERROR;
}

spin_unlock(&m->client->lock);
--
2.35.1