Hi Marcel, On Sat, Dec 19, 2009 at 1:02 AM, Marcel Holtmann <marcel@xxxxxxxxxxxx> wrote: > 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. We have this patch also in Nokia N900 phone. And this was the best solution for the problem mentioned. > 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. What do you think about following comment: --- a/net/bluetooth/rfcomm/core.c +++ b/net/bluetooth/rfcomm/core.c @@ -1151,7 +1151,11 @@ static int rfcomm_recv_ua(struct rfcomm_session *s, u8 dlci) break; case BT_DISCONN: - rfcomm_session_put(s); + /* When socket is closed and we are not RFCOMM + * initiator rfcomm_process_rx already calls + * rfcomm_session_put */ + if (s->sock->sk->sk_state != BT_CLOSED) + rfcomm_session_put(s); break; } } -- Regards Andrei -- 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
