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43a556b2fd
rfcomm_sock_recvmsg() completes a deferred setup by calling
rfcomm_dlc_accept() without holding any RFCOMM lock:
if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) {
rfcomm_dlc_accept(d);
return 0;
}
and rfcomm_dlc_accept() dereferences the session on its first line:
struct sock *sk = d->session->sock->sk;
Every other path that touches d->session runs under rfcomm_mutex:
rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),
rfcomm_dlc_send_rpn(), and the RFCOMM thread through
rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as
"called under rfcomm_lock()". This call site is the only one that skips
it.
The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against
teardown, since __rfcomm_dlc_close() returns early when it wins the
test_and_clear. But rfcomm_recv_disc() forces the state first:
d->state = BT_CLOSED;
__rfcomm_dlc_close(d, err);
and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and
BT_CONNECT2. With the state already BT_CLOSED that switch does not
match, the bit is never consulted, and __rfcomm_dlc_close() falls
through to rfcomm_dlc_unlink(), which sets d->session = NULL.
So a remote DISC on a deferred dlc clears the session while leaving
RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the
test_and_clear and dereferences a NULL session. No timing window is
needed: once the DISC has been processed, the dereference is
unconditional.
Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and
rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and
re-checks the session, around a __rfcomm_dlc_accept() that the two
in-core callers, which already hold the mutex, keep using.
Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated
over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the
RFCOMM PSM, starts a session, opens a dlc on a channel bound with
BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on
the accepted socket then hits:
Oops: general protection fault
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
RIP: 0010:rfcomm_dlc_accept+0x54/0x350
Call Trace:
rfcomm_sock_recvmsg+0x1cd/0x230
sock_recvmsg+0x166/0x1c0
__sys_recvfrom+0x20d/0x300
0x10 is the offset of sock in struct rfcomm_session. With this patch the
same run completes with recv() returning 0 and no report, and lockdep
stays quiet, confirming rfcomm_mutex is still taken before lock_sock on
this path as it is on the thread side.
Fixes:
|
||
|---|---|---|
| .. | ||
| bnep | ||
| hidp | ||
| rfcomm | ||
| 6lowpan.c | ||
| af_bluetooth.c | ||
| aosp.c | ||
| aosp.h | ||
| coredump.c | ||
| ecdh_helper.c | ||
| ecdh_helper.h | ||
| eir.c | ||
| eir.h | ||
| hci_codec.c | ||
| hci_codec.h | ||
| hci_conn.c | ||
| hci_core.c | ||
| hci_debugfs.c | ||
| hci_debugfs.h | ||
| hci_drv.c | ||
| hci_event.c | ||
| hci_sock.c | ||
| hci_sync.c | ||
| hci_sysfs.c | ||
| iso.c | ||
| Kconfig | ||
| l2cap_core.c | ||
| l2cap_sock.c | ||
| leds.c | ||
| leds.h | ||
| lib.c | ||
| Makefile | ||
| mgmt_config.c | ||
| mgmt_config.h | ||
| mgmt_util.c | ||
| mgmt_util.h | ||
| mgmt.c | ||
| msft.c | ||
| msft.h | ||
| sco.c | ||
| selftest.c | ||
| selftest.h | ||
| smp.c | ||
| smp.h | ||