9p/trans_fd: abort p9_read_work if req status changed

[ Upstream commit e4ca13f7d075e551dc158df6af18fb412a1dba0a ]

p9_read_work would try to handle an errored req even if it got put to
error state by another thread between the lookup (that worked) and the
time it had been fully read.
The request itself is safe to use because we hold a ref to it from the
lookup (for m->rreq, so it was safe to read into the request data buffer
until this point), but the req_list has been deleted at the same time
status changed, and client_cb already has been called as well, so we
should not do either.

Link: http://lkml.kernel.org/r/1539057956-23741-1-git-send-email-asmadeus@codewreck.org
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Reported-by: syzbot+2222c34dc40b515f30dc@syzkaller.appspotmail.com
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index aa4586672cee9936bec498342d10b7cc2f082ceb..91f71958c2e162bb4e802ffd106094894938a69f 100644 (file)
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -295,7 +295,6 @@ static void p9_read_work(struct work_struct *work)
 {
        int n, err;
        struct p9_conn *m;
-       int status = REQ_STATUS_ERROR;
 
        m = container_of(work, struct p9_conn, rq);
 
@@ -375,11 +374,17 @@ static void p9_read_work(struct work_struct *work)
        if ((m->req) && (m->rc.offset == m->rc.capacity)) {
                p9_debug(P9_DEBUG_TRANS, "got new packet\n");
                spin_lock(&m->client->lock);
-               if (m->req->status != REQ_STATUS_ERROR)
-                       status = REQ_STATUS_RCVD;
-               list_del(&m->req->req_list);
-               /* update req->status while holding client->lock  */
-               p9_client_cb(m->client, m->req, status);
+               if (m->req->status == REQ_STATUS_SENT) {
+                       list_del(&m->req->req_list);
+                       p9_client_cb(m->client, m->req, REQ_STATUS_RCVD);
+               } else {
+                       spin_unlock(&m->client->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);
                m->rc.sdata = NULL;
                m->rc.offset = 0;