On Thu, Feb 6, 2020 at 3:38 PM Michael Niedermayer <michae...@gmx.at> wrote:
> On Thu, Jan 30, 2020 at 11:23:07AM -0800, Dale Curtis wrote:
> > On Wed, Jan 29, 2020 at 10:23 PM Michael Niedermayer
> <mich...@niedermayer.cc>
> > wrote:
> >
> > > so i think it works but maybe ive missed something, for which values
> > > of e2_pts do you see a problem with e1_pts = INT64_MIN?
> > >
> >
> > For e1_pts = INT64_MIN and e2_pts >= 0 you end up with a negative int64_t
> > result for e2_pts - (uint64_t)e1_pts, so it's always < time_tolerance. If
> > that's what you intended, then sgtm.
>
> thats what the code would do if the elemnts where large enough to not
> overflow
> so that seems to match whats intended.
>
> Do you see some issue here ?
>
Whoops, sorry, I just realized my previous comment was rejected from the
list since I used the wrong e-mail address. My previous statement was
incorrect. The code you proposed correctly promotes a uint64_t and not an
int64_t when used in a conditional. Here's what I wrote that got lost:
"Actually, this was a test construction error on my part. In a conditional
this does evaluate to a uint64_t vs int64_t, so the comparison is valid.
I've attached your recommended patch. Thanks for your patience."
- dale
From c50d0a347fc779c71c07757d9cad8a7d56eb857b Mon Sep 17 00:00:00 2001
From: Dale Curtis <dalecur...@chromium.org>
Date: Tue, 28 Jan 2020 16:49:14 -0800
Subject: [PATCH] Fix undefined behavior in ff_configure_buffers_for_index()
When e2_pts == INT64_MIN and e1_pts >= 0 the calculation of
e2_pts - e1_pts will overflow an int64_t.
Signed-off-by: Dale Curtis <dalecur...@chromium.org>
---
libavformat/utils.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/libavformat/utils.c b/libavformat/utils.c
index e22ca7cab8..81ea239a66 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -2108,6 +2108,8 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
//We could use URLProtocol flags here but as many user applications do not use URLProtocols this would be unreliable
const char *proto = avio_find_protocol_name(s->url);
+ av_assert0(time_tolerance >= 0);
+
if (!proto) {
av_log(s, AV_LOG_INFO,
"Protocol name not provided, cannot determine if input is local or "
@@ -2135,7 +2137,7 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
for (; i2 < st2->nb_index_entries; i2++) {
AVIndexEntry *e2 = &st2->index_entries[i2];
int64_t e2_pts = av_rescale_q(e2->timestamp, st2->time_base, AV_TIME_BASE_Q);
- if (e2_pts - e1_pts < time_tolerance)
+ if (e2_pts < e1_pts || e2_pts - (uint64_t)e1_pts < time_tolerance)
continue;
pos_delta = FFMAX(pos_delta, e1->pos - e2->pos);
break;
--
2.25.0.341.g760bfbb309-goog
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