linux-kernel - Re: KASAN: use-after-free in __mutex

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Message-Id: <20220930160843.818893-1-iam@sung-woo.kim>
Date:   Fri, 30 Sep 2022 12:08:44 -0400
From:   Sungwoo Kim <iam@...g-woo.kim>
To:     luiz.dentz@...il.com
Cc:     davem@...emloft.net, edumazet@...gle.com, iam@...g-woo.kim,
        johan.hedberg@...il.com, kuba@...nel.org,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        marcel@...tmann.org, netdev@...r.kernel.org, pabeni@...hat.com,
        syzkaller@...glegroups.com
Subject: Re: KASAN: use-after-free in __mutex_lock

Hi Dentz,
How about to use l2cap_get_chan_by_scid because it looks resposible to
handle ref_cnt.

Signed-off-by: Sungwoo Kim <iam@...g-woo.kim>
---
 net/bluetooth/l2cap_core.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 2c9de67da..d3a074cbc 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4291,26 +4291,18 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 	BT_DBG("dcid 0x%4.4x scid 0x%4.4x result 0x%2.2x status 0x%2.2x",
 	       dcid, scid, result, status);
 
-	mutex_lock(&conn->chan_lock);
-
 	if (scid) {
-		chan = __l2cap_get_chan_by_scid(conn, scid);
-		if (!chan) {
-			err = -EBADSLT;
-			goto unlock;
-		}
+		chan = l2cap_get_chan_by_scid(conn, scid);
+		if (!chan)
+			return -EBADSLT;
 	} else {
-		chan = __l2cap_get_chan_by_ident(conn, cmd->ident);
-		if (!chan) {
-			err = -EBADSLT;
-			goto unlock;
-		}
+		chan = l2cap_get_chan_by_ident(conn, cmd->ident);
+		if (!chan)
+			return -EBADSLT;
 	}
 
 	err = 0;
 
-	l2cap_chan_lock(chan);
-
 	switch (result) {
 	case L2CAP_CR_SUCCESS:
 		l2cap_state_change(chan, BT_CONFIG);
@@ -4336,9 +4328,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 	}
 
 	l2cap_chan_unlock(chan);
-
-unlock:
-	mutex_unlock(&conn->chan_lock);
+	l2cap_chan_put(chan);
 
 	return err;
 }
-- 
2.25.1