Hello Jenkins Builder,
I'd like you to reexamine a change. Please visit
https://gerrit.osmocom.org/13277
to look at the new patch set (#2).
Change subject: add caller-owns-msgb variant osmo_sccp_user_sap_down_nofree()
......................................................................
add caller-owns-msgb variant osmo_sccp_user_sap_down_nofree()
Add osmo_sccp_user_sap_down_nofree(), which is identical to
osmo_sccp_user_sap_down(), but doesn't imply a msgb_free().
To implement that, sccp_sclc_user_sap_down_nofree() with the same msgb
semantics is required.
Rationale:
Avoiding msgb leaks is easiest if the caller retains ownership of the msgb.
Take this hypothetical chain where leaks are obviously avoided:
void send()
{
msg = msgb_alloc();
dispatch(msg);
msgb_free(msg);
}
void dispatch(msg)
{
osmo_fsm_inst_dispatch(fi, msg);
}
void fi_on_event(fi, data)
{
if (socket_is_ok)
socket_write((struct msgb*)data);
}
void socket_write(msgb)
{
if (!ok1)
return;
if (ok2) {
if (!ok3)
return;
write(sock, msg->data);
}
}
However, if the caller passes ownership down to the msgb consumer, things
become nightmarishly complex:
void send()
{
msg = msgb_alloc();
rc = dispatch(msg);
/* dispatching event failed? */
if (rc)
msgb_free(msg);
}
int dispatch(msg)
{
if (osmo_fsm_inst_dispatch(fi, msg))
return -1;
if (something_else())
return -1; // <-- double free!
}
void fi_on_event(fi, data)
{
if (socket_is_ok) {
socket_write((struct msgb*)data);
else
/* socket didn't consume? */
msgb_free(data);
}
int socket_write(msgb)
{
if (!ok1)
return -1; // <-- leak!
if (ok2) {
if (!ok3)
goto out;
write(sock, msg->data);
}
out:
msgb_free(msg);
return -2;
}
If any link in this call chain fails to be aware of the importance to return a
failed RC or to free a msgb if the chain is broken, or to not return a failed
RC if the msgb is consumed, we have a hidden msgb leak or double free.
This is the case with osmo_sccp_user_sap_down(). In new osmo-msc, passing data
through various FSM instances, there is high potential for leak/double-free
bugs. A very large brain is required to track down every msgb path.
osmo_sccp_user_sap_down_nofree() makes this problem trivial to solve even for
humans.
Change-Id: Ic818efa78b90f727e1a94c18b60d9a306644f340
---
M include/osmocom/sigtran/sccp_sap.h
M src/sccp_internal.h
M src/sccp_sclc.c
M src/sccp_scoc.c
4 files changed, 38 insertions(+), 23 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/libosmo-sccp refs/changes/77/13277/2
--
To view, visit https://gerrit.osmocom.org/13277
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Gerrit-Project: libosmo-sccp
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ic818efa78b90f727e1a94c18b60d9a306644f340
Gerrit-Change-Number: 13277
Gerrit-PatchSet: 2
Gerrit-Owner: Neels Hofmeyr <[email protected]>
Gerrit-Reviewer: Jenkins Builder (1000002)
Gerrit-Reviewer: Neels Hofmeyr <[email protected]>
Gerrit-CC: Harald Welte <[email protected]>
