[PATCH v2 1/2] Bluetooth: ISO: Fix data-race on dst in iso_sock_connect()

[SeungJu Cheon <suunj1331@gmail.com>]

iso_sock_connect() copies the destination address into
iso_pi(sk)->dst under lock_sock, then releases the lock and reads
it back with bacmp() to decide between the CIS and BIS connect
paths:

    lock_sock(sk);
    bacpy(&iso_pi(sk)->dst, &sa->iso_bdaddr);
    iso_pi(sk)->dst_type = sa->iso_bdaddr_type;
    release_sock(sk);

    if (bacmp(&iso_pi(sk)->dst, BDADDR_ANY))  // <- no lock held

This read after release_sock() races with any concurrent write to
iso_pi(sk)->dst on the same socket.

Fix by reading the destination address directly from the local
sockaddr argument (sa->iso_bdaddr) instead of iso_pi(sk)->dst.
Since sa is a function-local argument, reading it requires no
locking and avoids the race.

This patch addresses only the bacmp() race in iso_sock_connect();
other unprotected iso_pi(sk) accesses are fixed separately in the
next patch.

KCSAN report:

BUG: KCSAN: data-race in memcmp+0x39/0xb0

race at unknown origin, with read to 0xffff8f96ea66dde3 of 1 bytes by task 549 on cpu 1:
 memcmp+0x39/0xb0
 iso_sock_connect+0x275/0xb40
 __sys_connect_file+0xbd/0xe0
 __sys_connect+0xe0/0x110
 __x64_sys_connect+0x40/0x50
 x64_sys_call+0xcad/0x1c60
 do_syscall_64+0x133/0x590
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00 -> 0xee

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 549 Comm: iso_race_combin Not tainted 7.0.0-08391-g1d51b370a0f8 #40 PREEMPT(lazy)

Fixes: ccf74f2390d6 ("Bluetooth: Add BTPROTO_ISO socket type")
Signed-off-by: SeungJu Cheon <suunj1331@gmail.com>
---
 net/bluetooth/iso.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
index be145e2736b7..290a1b9a9daa 100644
--- a/net/bluetooth/iso.c
+++ b/net/bluetooth/iso.c
@@ -1193,7 +1193,7 @@ static int iso_sock_connect(struct socket *sock, struct sockaddr_unsized *addr,
 
 	release_sock(sk);
 
-	if (bacmp(&iso_pi(sk)->dst, BDADDR_ANY))
+	if (bacmp(&sa->iso_bdaddr, BDADDR_ANY))
 		err = iso_connect_cis(sk);
 	else
 		err = iso_connect_bis(sk);
-- 
2.52.0