On Wed, Feb 3, 2010 at 12:21 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. >> >> 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; >> } >> } > > looks good. Just turn this into a proper patch and send it to the > mailing list so I can apply it. Sent. 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
