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Subject[PATCH 4.9 35/78] net/9p/trans_fd.c: fix race by holding the lock
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tomas Bortoli <tomasbortoli@gmail.com>

[ Upstream commit 9f476d7c540cb57556d3cc7e78704e6cd5100f5f ]

It may be possible to run p9_fd_cancel() with a deleted req->req_list
and incur in a double del. To fix hold the client->lock while changing
the status, so the other threads will be synchronized.

Link: http://lkml.kernel.org/r/20180723184253.6682-1-tomasbortoli@gmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+735d926e9d1317c3310c@syzkaller.appspotmail.com
To: Eric Van Hensbergen <ericvh@gmail.com>
To: Ron Minnich <rminnich@sandia.gov>
To: Latchesar Ionkov <lucho@ionkov.net>
Cc: Yiwen Jiang <jiangyiwen@huwei.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/9p/trans_fd.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -195,15 +195,14 @@ static void p9_mux_poll_stop(struct p9_c
static void p9_conn_cancel(struct p9_conn *m, int err)
{
struct p9_req_t *req, *rtmp;
- unsigned long flags;
LIST_HEAD(cancel_list);

p9_debug(P9_DEBUG_ERROR, "mux %p err %d\n", m, err);

- spin_lock_irqsave(&m->client->lock, flags);
+ spin_lock(&m->client->lock);

if (m->err) {
- spin_unlock_irqrestore(&m->client->lock, flags);
+ spin_unlock(&m->client->lock);
return;
}

@@ -215,7 +214,6 @@ static void p9_conn_cancel(struct p9_con
list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
list_move(&req->req_list, &cancel_list);
}
- spin_unlock_irqrestore(&m->client->lock, flags);

list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
@@ -224,6 +222,7 @@ static void p9_conn_cancel(struct p9_con
req->t_err = err;
p9_client_cb(m->client, req, REQ_STATUS_ERROR);
}
+ spin_unlock(&m->client->lock);
}

static int
@@ -379,8 +378,9 @@ static void p9_read_work(struct work_str
if (m->req->status != REQ_STATUS_ERROR)
status = REQ_STATUS_RCVD;
list_del(&m->req->req_list);
- spin_unlock(&m->client->lock);
+ /* update req->status while holding client->lock */
p9_client_cb(m->client, m->req, status);
+ spin_unlock(&m->client->lock);
m->rc.sdata = NULL;
m->rc.offset = 0;
m->rc.capacity = 0;

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