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authorVadim Yanitskiy <axilirator@gmail.com>2020-03-11 03:00:22 +0700
committerlaforge <laforge@osmocom.org>2020-03-16 10:32:42 +0000
commitd944f1d89db89ab473a7df8363e2339dfd8f2411 (patch)
tree8c998cd7e3e58e1852f2ee2ca36dc897f14df1bf
parent9d3c2d047bf21f2d25eac3bb84064291fe5fcb9e (diff)
trxcon/scheduler: be safe against a theoretical integer overflow
As was noted by Pau Espin Pedrol, there is a theoretical chance that lchan->tdma.num_proc would overflow, so as a consequence, subst_frame_loss() will be unable to compensate one (potentionally lost) Downlink burst. On practice, given the size of unsigned long and duration of a single TDMA frame, it would only happen once in roughly ~6 years. FRAME_DURATION = 4615 * 10e-6 ULONG_MAX = 2 ** 32 - 1 FRAME_DURATION * ULONG_MAX -> ~198212740 seconds -> ~55059 hours -> ~2294 days -> ~6 years. Chances are that trxcon would crash much earlier, or even GSM would be completely forgotten after such a long time run, but let's work this around and simply start counting from 1 if that overflow eventually happens. Change-Id: I3d40ef09b06039a85df52af06ab38de314e1a434
-rw-r--r--src/host/trxcon/sched_trx.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/src/host/trxcon/sched_trx.c b/src/host/trxcon/sched_trx.c
index 1efae247..b53b0e83 100644
--- a/src/host/trxcon/sched_trx.c
+++ b/src/host/trxcon/sched_trx.c
@@ -721,7 +721,16 @@ int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
/* Update TDMA frame statistics */
lchan->tdma.last_proc = fn;
- lchan->tdma.num_proc++;
+
+ if (++lchan->tdma.num_proc == 0) {
+ /* Theoretically, we may have an integer overflow of num_proc counter.
+ * As a consequence, subst_frame_loss() will be unable to compensate
+ * one (potentionally lost) Downlink burst. On practice, it would
+ * happen once in 4615 * 10e-6 * (2 ^ 32 - 1) seconds or ~6 years. */
+ LOGP(DSCHD, LOGL_NOTICE, "Too many TDMA frames have been processed. "
+ "Are you running trxcon for more than 6 years?!?\n");
+ lchan->tdma.num_proc = 1;
+ }
return 0;
}