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Subject[PATCH] net/9p/trans_fd.c: fix double list_del() and race in access
Date
This patch uses list_del_init() instead of list_del() to eliminate "req_list". This to prevent double list_del()'s calls to the same list from provoking a GPF. Furthermore, this patch fixes an access to "req_list" that was made without getting the relative lock.

Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+735d926e9d1317c3310c@syzkaller.appspotmail.com
---

net/9p/trans_fd.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index a64b01c56e30..131bb1f059e6 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -223,7 +223,9 @@ static void p9_conn_cancel(struct p9_conn *m, int err)

list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
- list_del(&req->req_list);
+ spin_lock_irqsave(&m->client->lock, flags);
+ list_del_init(&req->req_list);
+ spin_unlock_irqrestore(&m->client->lock, flags);
if (!req->t_err)
req->t_err = err;
p9_client_cb(m->client, req, REQ_STATUS_ERROR);
@@ -369,7 +371,7 @@ static void p9_read_work(struct work_struct *work)
spin_lock(&m->client->lock);
if (m->req->status != REQ_STATUS_ERROR)
status = REQ_STATUS_RCVD;
- list_del(&m->req->req_list);
+ list_del_init(&m->req->req_list);
spin_unlock(&m->client->lock);
p9_client_cb(m->client, m->req, status);
m->rc.sdata = NULL;
@@ -684,7 +686,7 @@ static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
spin_lock(&client->lock);

if (req->status == REQ_STATUS_UNSENT) {
- list_del(&req->req_list);
+ list_del_init(&req->req_list);
req->status = REQ_STATUS_FLSHD;
ret = 0;
}
@@ -701,7 +703,7 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
* remove it from the list.
*/
spin_lock(&client->lock);
- list_del(&req->req_list);
+ list_del_init(&req->req_list);
spin_unlock(&client->lock);

return 0;
--
2.11.0
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