Hi Nick, > >> 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. the RFCOMM reference counting is something nasty and it does need to be re-written. One thing that needs to happen that we stop using the L2CAP sockets directly. We have to put a proper L2CAP in-kernel specific API in between that ensures we are not mixing things. That is the one issues that we always had in this area. Before applying this patch, I like to have additionally a comment in front of this conditional put call that explains a little bit the problem area here. The long explanation with logs etc. should be in the commit message. I have to make sure that we fully understand what is going on here and why we did it. Regards Marcel -- 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
