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

[Michael Niedermayer]

On Thu, Aug 17, 2017 at 10:49:37AM +0800, Zhao Zhili wrote:
> 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
> >
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> >

>  ffprobe.c |    1 +
>  1 file changed, 1 insertion(+)
> 24395943b86a20ae2da6cb2f6f11ca6bdede48d9  0001-ffprobe-fix-use-of-uninitialized-variable.patch
> From c1e0bc31dcbda714eb589d40f756580266ba6b14 Mon Sep 17 00:00:00 2001
> From: Zhao Zhili <wantlamy at gmail.com>
> Date: Thu, 17 Aug 2017 10:24:01 +0800
> Subject: [PATCH] ffprobe: fix use of uninitialized variable
> 
> ---
>  ffprobe.c | 1 +
>  1 file changed, 1 insertion(+)

applied

thanks

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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