diff options
| author | Vadim Yanitskiy <axilirator@gmail.com> | 2020-03-11 03:00:22 +0700 |
|---|---|---|
| committer | laforge <laforge@osmocom.org> | 2020-03-16 10:32:42 +0000 |
| commit | d944f1d89db89ab473a7df8363e2339dfd8f2411 (patch) | |
| tree | 8c998cd7e3e58e1852f2ee2ca36dc897f14df1bf /src | |
| parent | 9d3c2d047bf21f2d25eac3bb84064291fe5fcb9e (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
Diffstat (limited to 'src')
| -rw-r--r-- | src/host/trxcon/sched_trx.c | 11 |
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; } |