[FFmpeg-devel] [PATCH] ffprobe: fix use of uninitialized variable

[Zhao Zhili]

On Thu, Aug 17, 2017 at 3:24 AM, Michael Niedermayer <michael at niedermayer.cc
> wrote:

> On Wed, Aug 09, 2017 at 01:05:11PM +0800, Zhao Zhili wrote:
> > On Wed, Aug 9, 2017 at 1:23 AM, Michael Niedermayer
> <michael at niedermayer.cc>
> > wrote:
> >
> > > On Sun, Aug 06, 2017 at 03:39:07PM +0800, Zhao Zhili wrote:
> > > > ---
> > > >  ffprobe.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/ffprobe.c b/ffprobe.c
> > > > index f22c4f57ad..ac9ff051fa 100644
> > > > --- a/ffprobe.c
> > > > +++ b/ffprobe.c
> > > > @@ -3328,6 +3328,7 @@ static int parse_read_interval(const char
> > > > *interval_spec,
> > > >              }
> > > >              interval->end = lli;
> > > >          } else {
> > > > +            interval->duration_frames = 0;
> > > >              ret = av_parse_time(&us, p, 1);
> > > >              if (ret < 0) {
> > > >                  av_log(NULL, AV_LOG_ERROR, "Invalid interval
> > > end/duration
> > > > specification '%s'\n", p);
> > > > @@ -3337,6 +3338,7 @@ static int parse_read_interval(const char
> > > > *interval_spec,
> > > >          }
> > > >      } else {
> > > >          interval->has_end = 0;
> > > > +        interval->duration_frames = 0;
> > > >      }
> > > >
> > > >  end:
> > > > @@ -3357,7 +3359,7 @@ static int parse_read_intervals(const char
> > > > *intervals_spec)
> > > >              n++;
> > > >      n++;
> > > >
> > > > -    read_intervals = av_malloc_array(n, sizeof(*read_intervals));
> > > > +    read_intervals = av_mallocz_array(n, sizeof(*read_intervals));
> > > >      if (!read_intervals) {
> > > >          ret = AVERROR(ENOMEM);
> > > >          goto end;
> > > > --
> > > > 2.13.2
> > >
> > > >  ffprobe.c |    4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > > 59efe1bf808d9621c14252fd0e71dc4b9a635c7a  0001-ffprobe-fix-use-of-
> > > uninitialized-variable.patch
> > > > From 1d3fe1eb4cd27efc337a1fae302f5539e3c7459b Mon Sep 17 00:00:00
> 2001
> > > > From: Zhao Zhili <wantlamy at gmail.com>
> > > > Date: Sun, 6 Aug 2017 15:33:42 +0800
> > > > Subject: [PATCH] ffprobe: fix use of uninitialized variable
> > > >
> > > > ---
> > > >  ffprobe.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/ffprobe.c b/ffprobe.c
> > > > index f22c4f57ad..ac9ff051fa 100644
> > > > --- a/ffprobe.c
> > > > +++ b/ffprobe.c
> > > > @@ -3328,6 +3328,7 @@ static int parse_read_interval(const char
> > > *interval_spec,
> > > >              }
> > > >              interval->end = lli;
> > > >          } else {
> > > > +            interval->duration_frames = 0;
> > > >              ret = av_parse_time(&us, p, 1);
> > > >              if (ret < 0) {
> > > >                  av_log(NULL, AV_LOG_ERROR, "Invalid interval
> > > end/duration specification '%s'\n", p);
> > >
>
> > > > @@ -3337,6 +3338,7 @@ static int parse_read_interval(const char
> > > *interval_spec,
> > > >          }
> > > >      } else {
> > > >          interval->has_end = 0;
> > > > +        interval->duration_frames = 0;
> > > >      }
> > >
> > > isnt has_end and end_is_offset 0 here and all uses of duration_frames
> > > under code checking either ?
> > >
> > >
> > If end_is_offset is 1 and *p is not '#', then duration_frames is not
> > initialized.
>
> The code quoted above is under the else, while the only code setting
> end_is_offset is under the if() side.
> how can you have end_is_offset == 1 without duration_frames being
> set ?
>
> further your patch allocates the intervals with av_mallocz_array()
> how can they be uninitialized if they are cleared during allocation?
>
> To me it looks like your code initializes the variable 3 times
> 2 are unneeded.
> But this is not code i know well so it may be that iam missing
> something
>
>
Sorry, I misunderstood your comment before. Yes there is only one place
which duration_frames
must be initialized. A new patch is attached.



>
>
> > So check end_is_offset doesn't prevent access uninitialized
> > value. And the current code didn't always check end_is_offset before
> access
> > duration_frames.
> >
> > A simple test case:
> > ffprobe -show_frames -select_streams v -read_intervals '%+60' foo
>
> yes i can drop 2 hunks of the patch and it still fixes the issue
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Those who would give up essential Liberty, to purchase a little
> temporary Safety, deserve neither Liberty nor Safety -- Benjamin Franklin
>
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