fftools/ffmpeg_opt: Check attachment filesize

The data of an attachment file is put into an AVCodecParameter's
extradata. The corresponding size field has type int, yet there was no
check for the size to fit into an int. As a consequence, it was possible
to create extradata with negative size (by using a big enough max_alloc).

Other errors were also possible: If SIZE_MAX < INT64_MAX (e.g. on 32bit
systems) then the file size might be truncated before the allocation;
and avio_read() takes an int, too, so one would not have read as much
as one desired.

Furthermore, the extradata is now padded as is required.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 889ad93c8839e5ac1ec28bc8e1fea6df71b9bf80)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
index 56d6e2f101..e89afe958e 100644
--- a/ffmpeg_opt.c
+++ b/ffmpeg_opt.c
@@ -2300,12 +2300,14 @@ loop_end:
                    o->attachments[i]);
             exit_program(1);
         }
-        if (!(attachment = av_malloc(len))) {
-            av_log(NULL, AV_LOG_FATAL, "Attachment %s too large to fit into memory.\n",
+        if (len > INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE ||
+            !(attachment = av_malloc(len + AV_INPUT_BUFFER_PADDING_SIZE))) {
+            av_log(NULL, AV_LOG_FATAL, "Attachment %s too large.\n",
                    o->attachments[i]);
             exit_program(1);
         }
         avio_read(pb, attachment, len);
+        memset(attachment + len, 0, AV_INPUT_BUFFER_PADDING_SIZE);
 
         ost = new_attachment_stream(o, oc, -1);
         ost->stream_copy               = 0;