<p>laforge <strong>submitted</strong> this change.</p><p><a href="https://gerrit.osmocom.org/c/osmocom-bb/+/17449">View Change</a></p><div style="white-space:pre-wrap">Approvals:
laforge: Looks good to me, approved
pespin: Looks good to me, but someone else must approve
Jenkins Builder: Verified
</div><pre style="font-family: monospace,monospace; white-space: pre-wrap;">trxcon/scheduler: be safe against a theoretical integer overflow<br><br>As was noted by Pau Espin Pedrol, there is a theoretical chance<br>that lchan->tdma.num_proc would overflow, so as a consequence,<br>subst_frame_loss() will be unable to compensate one<br>(potentionally lost) Downlink burst.<br><br>On practice, given the size of unsigned long and duration of a<br>single TDMA frame, it would only happen once in roughly ~6 years.<br><br> FRAME_DURATION = 4615 * 10e-6<br> ULONG_MAX = 2 ** 32 - 1<br><br> FRAME_DURATION * ULONG_MAX -> ~198212740 seconds<br> -> ~55059 hours<br> -> ~2294 days<br> -> ~6 years.<br><br>Chances are that trxcon would crash much earlier, or even GSM<br>would be completely forgotten after such a long time run, but<br>let's work this around and simply start counting from 1<br>if that overflow eventually happens.<br><br>Change-Id: I3d40ef09b06039a85df52af06ab38de314e1a434<br>---<br>M src/host/trxcon/sched_trx.c<br>1 file changed, 10 insertions(+), 1 deletion(-)<br><br></pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;"><span>diff --git a/src/host/trxcon/sched_trx.c b/src/host/trxcon/sched_trx.c</span><br><span>index 1efae24..b53b0e8 100644</span><br><span>--- a/src/host/trxcon/sched_trx.c</span><br><span>+++ b/src/host/trxcon/sched_trx.c</span><br><span>@@ -721,7 +721,16 @@</span><br><span> </span><br><span> /* Update TDMA frame statistics */</span><br><span> lchan->tdma.last_proc = fn;</span><br><span style="color: hsl(0, 100%, 40%);">- lchan->tdma.num_proc++;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ if (++lchan->tdma.num_proc == 0) {</span><br><span style="color: hsl(120, 100%, 40%);">+ /* Theoretically, we may have an integer overflow of num_proc counter.</span><br><span style="color: hsl(120, 100%, 40%);">+ * As a consequence, subst_frame_loss() will be unable to compensate</span><br><span style="color: hsl(120, 100%, 40%);">+ * one (potentionally lost) Downlink burst. On practice, it would</span><br><span style="color: hsl(120, 100%, 40%);">+ * happen once in 4615 * 10e-6 * (2 ^ 32 - 1) seconds or ~6 years. */</span><br><span style="color: hsl(120, 100%, 40%);">+ LOGP(DSCHD, LOGL_NOTICE, "Too many TDMA frames have been processed. "</span><br><span style="color: hsl(120, 100%, 40%);">+ "Are you running trxcon for more than 6 years?!?\n");</span><br><span style="color: hsl(120, 100%, 40%);">+ lchan->tdma.num_proc = 1;</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span> </span><br><span> return 0;</span><br><span> }</span><br><span></span><br></pre><p>To view, visit <a href="https://gerrit.osmocom.org/c/osmocom-bb/+/17449">change 17449</a>. To unsubscribe, or for help writing mail filters, visit <a href="https://gerrit.osmocom.org/settings">settings</a>.</p><div itemscope itemtype="http://schema.org/EmailMessage"><div itemscope itemprop="action" itemtype="http://schema.org/ViewAction"><link itemprop="url" href="https://gerrit.osmocom.org/c/osmocom-bb/+/17449"/><meta itemprop="name" content="View Change"/></div></div>
<div style="display:none"> Gerrit-Project: osmocom-bb </div>
<div style="display:none"> Gerrit-Branch: master </div>
<div style="display:none"> Gerrit-Change-Id: I3d40ef09b06039a85df52af06ab38de314e1a434 </div>
<div style="display:none"> Gerrit-Change-Number: 17449 </div>
<div style="display:none"> Gerrit-PatchSet: 3 </div>
<div style="display:none"> Gerrit-Owner: fixeria <axilirator@gmail.com> </div>
<div style="display:none"> Gerrit-Reviewer: Jenkins Builder </div>
<div style="display:none"> Gerrit-Reviewer: laforge <laforge@osmocom.org> </div>
<div style="display:none"> Gerrit-Reviewer: pespin <pespin@sysmocom.de> </div>
<div style="display:none"> Gerrit-MessageType: merged </div>