On Fri, Dec 18, 2009 at 1:59 PM, Marcel Holtmann <marcel@xxxxxxxxxxxx> wrote: > Hi Andrei, > >> Processing a RFCOMM UA frame when the socket is closed and we were not >> the >> RFCOMM initiator would cause rfcomm_session_put() to be called twice >> during >> rfcomm_process_rx(). This would cause a kernel panic in >> rfcomm_session_close. >> >> This could be easily reproduced during disconnect with devices such as >> Motorola H270 that send RFCOMM UA followed quickly by L2CAP disconnect >> request. >> This hcidump for this looks like: >> >> 2009-09-21 17:22:37.788895 < ACL data: handle 1 flags 0x02 dlen 8 >> L2CAP(d): cid 0x0041 len 4 [psm 3] >> RFCOMM(s): DISC: cr 0 dlci 20 pf 1 ilen 0 fcs 0x7d >> 2009-09-21 17:22:37.906204 > HCI Event: Number of Completed Packets >> (0x13) >> plen 5 >> handle 1 packets 1 >> 2009-09-21 17:22:37.933090 > ACL data: handle 1 flags 0x02 dlen 8 >> L2CAP(d): cid 0x0040 len 4 [psm 3] >> RFCOMM(s): UA: cr 0 dlci 20 pf 1 ilen 0 fcs 0x57 >> 2009-09-21 17:22:38.636764 < ACL data: handle 1 flags 0x02 dlen 8 >> L2CAP(d): cid 0x0041 len 4 [psm 3] >> RFCOMM(s): DISC: cr 0 dlci 0 pf 1 ilen 0 fcs 0x9c >> 2009-09-21 17:22:38.744125 > HCI Event: Number of Completed Packets >> (0x13) >> plen 5 >> handle 1 packets 1 >> 2009-09-21 17:22:38.763687 > ACL data: handle 1 flags 0x02 dlen 8 >> L2CAP(d): cid 0x0040 len 4 [psm 3] >> RFCOMM(s): UA: cr 0 dlci 0 pf 1 ilen 0 fcs 0xb6 >> 2009-09-21 17:22:38.783554 > ACL data: handle 1 flags 0x02 dlen 12 >> L2CAP(s): Disconn req: dcid 0x0040 scid 0x0041 >> >> Avoid calling rfcomm_session_put() twice by skipping this call >> in rfcomm_recv_ua() if the socket is closed. >> >> Picked from: >> http://android.git.kernel.org/?p=kernel/common.git;a=commit;h=1048e007842da2d6440679e1ca80f45438a6369d >> >> Signed-off-by: Nick Pelly <npelly@xxxxxxxxxx> >> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx> >> --- >> net/bluetooth/rfcomm/core.c | 3 ++- >> 1 files changed, 2 insertions(+), 1 deletions(-) >> >> diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c >> index 0313e88..56ffcb8 100644 >> --- a/net/bluetooth/rfcomm/core.c >> +++ b/net/bluetooth/rfcomm/core.c >> @@ -1148,7 +1148,8 @@ static int rfcomm_recv_ua(struct rfcomm_session >> *s, u8 dlci) >> break; >> >> case BT_DISCONN: >> - rfcomm_session_put(s); >> + if (s->sock->sk->sk_state != BT_CLOSED) >> + rfcomm_session_put(s); >> break; >> } >> } > > I am not a big fan of conditionally decreasing reference counts. I do > think it would be better to fix this by holding an extra pair of > reference counts or actually fixing the imbalance. What about the other > patches I proposed? Your proposed patch was to add an extra hold() / put() reference count around the offending put(). I did test this patch, and found it does not fix the underlying imbalance, it just moves the kernel panic somewhere else. As best I can tell, my patch does address the underlying imbalance. It is in production on Android phones and seems to work well. As best I can tell, there is not a cleaner solution that does not involve significant refactoring of rfcomm refcounting. Nick -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
