diff mbox series

[FFmpeg-devel,1/1] avformat/assenc: avoid incorrect copy of null terminator

Message ID 20230127172047.1024276-2-tim@ngus.net
State New
Headers show
Series Handle ASS format subtitle encoding ambiguity | expand

Checks

Context Check Description
andriy/make_x86 success Make finished
andriy/make_fate_x86 success Make fate finished

Commit Message

Tim Angus Jan. 27, 2023, 5:20 p.m. UTC 
When writing a subtitle SSA/ASS subtitle file, the
AVCodecParameters::extradata buffer is written directly to the output.
In the case where the buffer is filled from a matroska source file
produced by some older versions of Handbrake, this buffer ends with a
null terminating character, which is then erroneously copied into the
middle of the output file. The refactoring here avoids this problem by
copying the source buffer, manually null terminating it, then treating
it as a string rather than a raw buffer. This way it is agnostic as to
whether the source buffer was null terminated or not.

Signed-off-by: Tim Angus <tim@ngus.net>
---
 libavformat/assenc.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

Comments

Tim Angus Feb. 8, 2023, 3 p.m. UTC | #1 
On 27/01/2023 17:20, Tim Angus wrote:
> When writing a subtitle SSA/ASS subtitle file, the
> AVCodecParameters::extradata buffer is written directly to the output.
> In the case where the buffer is filled from a matroska source file
> produced by some older versions of Handbrake, this buffer ends with a
> null terminating character, which is then erroneously copied into the
> middle of the output file. The refactoring here avoids this problem by
> copying the source buffer, manually null terminating it, then treating
> it as a string rather than a raw buffer. This way it is agnostic as to
> whether the source buffer was null terminated or not.
>
Could somebody give this a look please? Thanks.
diff mbox series

Patch

diff --git a/libavformat/assenc.c b/libavformat/assenc.c
index 1600f0a02b..4c9ea6f982 100644
--- a/libavformat/assenc.c
+++ b/libavformat/assenc.c
@@ -24,6 +24,7 @@ 
 #include "internal.h"
 
 #include "libavutil/opt.h"
+#include "libavutil/mem.h"
 
 typedef struct DialogueLine {
     int readorder;
@@ -55,6 +56,7 @@  static int write_header(AVFormatContext *s)
     avpriv_set_pts_info(s->streams[0], 64, 1, 100);
     if (par->extradata_size > 0) {
         size_t header_size = par->extradata_size;
+        char *header_string = NULL;
         uint8_t *trailer = strstr(par->extradata, "\n[Events]");
 
         if (trailer)
@@ -69,9 +71,20 @@  static int write_header(AVFormatContext *s)
                 ass->trailer = trailer;
         }
 
-        avio_write(s->pb, par->extradata, header_size);
-        if (par->extradata[header_size - 1] != '\n')
-            avio_write(s->pb, "\r\n", 2);
+        header_string = av_malloc(header_size + 1);
+        if (!header_string)
+            return AVERROR(ENOMEM);
+
+        memcpy(header_string, par->extradata, header_size);
+        header_string[header_size] = 0;
+
+        avio_printf(s->pb, "%s", header_string);
+
+        if (header_string[strlen(header_string) - 1] != '\n')
+            avio_printf(s->pb, "\r\n");
+
+        av_free(header_string);
+
         ass->ssa_mode = !strstr(par->extradata, "\n[V4+ Styles]");
         if (!strstr(par->extradata, "\n[Events]"))
             avio_printf(s->pb, "[Events]\r\nFormat: %s, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text\r\n",