[PATCH AUTOSEL 6.0 30/32] net/9p: use a dedicated spinlock for trans_fd

Sasha Levin
2022-10-18T00:11:37Z

From: Dominique Martinet <asmadeus@codewreck.org>

[ Upstream commit 296ab4a813841ba1d5f40b03190fd1bd8f25aab0 ]

Shamelessly copying the explanation from Tetsuo Handa's suggested
patch[1] (slightly reworded):
syzbot is reporting inconsistent lock state in p9_req_put()[2],
for p9_tag_remove() from p9_req_put() from IRQ context is using
spin_lock_irqsave() on "struct p9_client"->lock but trans_fd
(not from IRQ context) is using spin_lock().

Since the locks actually protect different things in client.c and in
trans_fd.c, just replace trans_fd.c's lock by a new one specific to the
transport (client.c's protect the idr for fid/tag allocations,
while trans_fd.c's protects its own req list and request status field
that acts as the transport's state machine)

Link: https://lore.kernel.org/r/20220904112928.1308799-1-asmadeus@codewreck.org
Link: https://lkml.kernel.org/r/2470e028-9b05-2013-7198-1fdad071d999@I-love.SAKURA.ne.jp [1]
Link: https://syzkaller.appspot.com/bug?extid=2f20b523930c32c160cc [2]
Reported-by: syzbot <syzbot+2f20b523930c32c160cc@syzkaller.appspotmail.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/trans_fd.c | 41 +++++++++++++++++++++++++----------------
1 file changed, 25 insertions(+), 16 deletions(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 90f8642a7cf3..0191f22d1ec3 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -91,6 +91,7 @@ struct p9_poll_wait {
* @mux_list: list link for mux to manage multiple connections (?)
* @client: reference to client instance for this connection
* @err: error state
+ * @req_lock: lock protecting req_list and requests statuses
* @req_list: accounting for requests which have been sent
* @unsent_req_list: accounting for requests that haven't been sent
* @rreq: read request
@@ -114,6 +115,7 @@ struct p9_conn {
struct list_head mux_list;
struct p9_client *client;
int err;
+ spinlock_t req_lock;
struct list_head req_list;
struct list_head unsent_req_list;
struct p9_req_t *rreq;
@@ -189,10 +191,10 @@ static void p9_conn_cancel(struct p9_conn *m, int err)

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

- spin_lock(&m->client->lock);
+ spin_lock(&m->req_lock);

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

@@ -205,7 +207,7 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
list_move(&req->req_list, &cancel_list);
}

- spin_unlock(&m->client->lock);
+ spin_unlock(&m->req_lock);

list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
@@ -360,7 +362,7 @@ static void p9_read_work(struct work_struct *work)
if ((m->rreq) && (m->rc.offset == m->rc.capacity)) {
p9_debug(P9_DEBUG_TRANS, "got new packet\n");
m->rreq->rc.size = m->rc.offset;
- spin_lock(&m->client->lock);
+ spin_lock(&m->req_lock);
if (m->rreq->status == REQ_STATUS_SENT) {
list_del(&m->rreq->req_list);
p9_client_cb(m->client, m->rreq, REQ_STATUS_RCVD);
@@ -369,14 +371,14 @@ static void p9_read_work(struct work_struct *work)
p9_debug(P9_DEBUG_TRANS,
"Ignore replies associated with a cancelled request\n");
} else {
- spin_unlock(&m->client->lock);
+ spin_unlock(&m->req_lock);
p9_debug(P9_DEBUG_ERROR,
"Request tag %d errored out while we were reading the reply\n",
m->rc.tag);
err = -EIO;
goto error;
}
- spin_unlock(&m->client->lock);
+ spin_unlock(&m->req_lock);
m->rc.sdata = NULL;
m->rc.offset = 0;
m->rc.capacity = 0;
@@ -454,10 +456,10 @@ static void p9_write_work(struct work_struct *work)
}

if (!m->wsize) {
- spin_lock(&m->client->lock);
+ spin_lock(&m->req_lock);
if (list_empty(&m->unsent_req_list)) {
clear_bit(Wworksched, &m->wsched);
- spin_unlock(&m->client->lock);
+ spin_unlock(&m->req_lock);
return;
}

@@ -472,7 +474,7 @@ static void p9_write_work(struct work_struct *work)
m->wpos = 0;
p9_req_get(req);
m->wreq = req;
- spin_unlock(&m->client->lock);
+ spin_unlock(&m->req_lock);
}

p9_debug(P9_DEBUG_TRANS, "mux %p pos %d size %d\n",
@@ -589,6 +591,7 @@ static void p9_conn_create(struct p9_client *client)
INIT_LIST_HEAD(&m->mux_list);
m->client = client;

+ spin_lock_init(&m->req_lock);
INIT_LIST_HEAD(&m->req_list);
INIT_LIST_HEAD(&m->unsent_req_list);
INIT_WORK(&m->rq, p9_read_work);
@@ -670,10 +673,10 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
if (m->err < 0)
return m->err;

- spin_lock(&client->lock);
+ spin_lock(&m->req_lock);
req->status = REQ_STATUS_UNSENT;
list_add_tail(&req->req_list, &m->unsent_req_list);
- spin_unlock(&client->lock);
+ spin_unlock(&m->req_lock);

if (test_and_clear_bit(Wpending, &m->wsched))
n = EPOLLOUT;
@@ -688,11 +691,13 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)

static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
{
+ struct p9_trans_fd *ts = client->trans;
+ struct p9_conn *m = &ts->conn;
int ret = 1;

p9_debug(P9_DEBUG_TRANS, "client %p req %p\n", client, req);

- spin_lock(&client->lock);
+ spin_lock(&m->req_lock);

if (req->status == REQ_STATUS_UNSENT) {
list_del(&req->req_list);
@@ -700,21 +705,24 @@ static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
p9_req_put(client, req);
ret = 0;
}
- spin_unlock(&client->lock);
+ spin_unlock(&m->req_lock);

return ret;
}

static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
{
+ struct p9_trans_fd *ts = client->trans;
+ struct p9_conn *m = &ts->conn;
+
p9_debug(P9_DEBUG_TRANS, "client %p req %p\n", client, req);

- spin_lock(&client->lock);
+ spin_lock(&m->req_lock);
/* Ignore cancelled request if message has been received
* before lock.
*/
if (req->status == REQ_STATUS_RCVD) {
- spin_unlock(&client->lock);
+ spin_unlock(&m->req_lock);
return 0;
}

@@ -723,7 +731,8 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
*/
list_del(&req->req_list);
req->status = REQ_STATUS_FLSHD;
- spin_unlock(&client->lock);
+ spin_unlock(&m->req_lock);
+
p9_req_put(client, req);

return 0;
--
2.35.1