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Bug #5676

closed

NULL-pointer de-reference of HNB context after HNB de-registration / reject

Added by laforge 3 months ago. Updated 4 days ago.

Status:
Resolved
Priority:
High
Assignee:
Target version:
-
Start date:
09/12/2022
Due date:
% Done:

100%

Spec Reference:

Description

I've looked a bit at the hnbap code in osmo-hnbw, and I think there's a bug related to the hnb_context.

  • we allocate a hnb_context when accept()ing the SCTP connection
  • we release (free) the context not just when the SCTP connection is down, but also when
    • not being able to transmit a HNB-REGISTER-REJ
    • receiving a HNB-DE-REGISTER-REQ (which is what we receive here)

However, if a remote peer would choose to send us any additional HNBAP or RUA messages over the same association later on, hnb_read_cb() would unconditionally de-reference hnb, which is now a NULL-pointer, in

 struct hnb_context *hnb = osmo_stream_srv_get_data(conn);
 ...
 msg->dst = hnb;
 ...
 hnb->hnbap_stream = msgb_sctp_stream(msg);
 ...
 hnb->rua_stream = msgb_sctp_stream(msg);

So either we guard against this and no longer accept traffic on such an SCTP association, or we don't free the HNB context before the assoc/socket is closed.

I think the latter is the better solution, as we are seeing some 3rd party HNB which are re-using the same association to continue to talk to the HNBGW without shutting it down and creating a new connection.

Actions #1

Updated by laforge 3 months ago

I pushed some proposed related patches to laforge/os5767, please take it from there.

Actions #2

Updated by pespin 3 months ago

sigsegv reproduced with this TTCN3 test:
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/29325 hnbgw: Introduce test TC_hnb_reregister_reuse_sctp_assoc

Program received signal SIGSEGV, Segmentation fault.
0x000055ee5507a77c in hnb_read_cb ()
#0  0x000055ee5507a77c in hnb_read_cb ()
#1  0x00007f193271120a in ?? ()
   from /usr/lib/x86_64-linux-gnu/libosmonetif.so.8
#2  0x00007f193273a0f8 in ?? ()
   from /usr/lib/x86_64-linux-gnu/libosmocore.so.19
#3  0x00007f193273a217 in osmo_select_main_ctx ()
   from /usr/lib/x86_64-linux-gnu/libosmocore.so.19
#4  0x000055ee5507bc2c in main ()
(gdb) quit
A debugging session is active.
Actions #3

Updated by pespin 4 days ago

  • Status changed from New to Resolved
  • % Done changed from 0 to 100

This has been fixed a while ago as part of SYS#6113.
See osmo-hnbgw c971c657c5ee44126616e599da83c8a6cb3a3921..930ed702b65e3049f410db73a2e93aa9bf0c7870

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