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avcodec/htmlsubtitles: Fixes denial of service due to use of sscanf in inner loop for handling braces

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Fixes: [Semmle Security Reports #19439]
Fixes: dos_sscanf2.mkv

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 894995c41e0795c7a44f81adc4838dedc3932e65)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Kevin Backhouse via RT 2019-02-06 12:56:01 +00:00 committed by Michael Niedermayer
parent 23ccf3cabb
commit 273f2755ce
1 changed files with 21 additions and 3 deletions
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24
libavcodec/htmlsubtitles.c
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@ -22,6 +22,7 @@
#include "libavutil/common.h"
#include "libavutil/parseutils.h"
#include "htmlsubtitles.h"
#include <ctype.h>
static int html_color_parse(void *log_ctx, const char *str)
{
@ -51,6 +52,25 @@ static void rstrip_spaces_buf(AVBPrint *buf)
buf->str[--buf->len] = 0;
}
/*
* Fast code for scanning text enclosed in braces. Functionally
* equivalent to this sscanf call:
*
* sscanf(in, "{\\an%*1u}%n", &len) >= 0 && len > 0
*/
static int scanbraces(const char* in) {
if (strncmp(in, "{\\an", 4) != 0) {
return 0;
}
if (!isdigit(in[4])) {
return 0;
}
if (in[5] != '}') {
return 0;
}
return 1;
}
/*
* Fast code for scanning the rest of a tag. Functionally equivalent to
* this sscanf call:
@ -110,9 +130,7 @@ int ff_htmlmarkup_to_ass(void *log_ctx, AVBPrint *dst, const char *in)
break;
case '{': /* skip all {\xxx} substrings except for {\an%d}
and all microdvd like styles such as {Y:xxx} */
len = 0;
an += sscanf(in, "{\\an%*1u}%n", &len) >= 0 && len > 0;
an += scanbraces(in);
if (!closing_brace_missing) {
if ( (an != 1 && in[1] == '\\')
|| (in[1] && strchr("CcFfoPSsYy", in[1]) && in[2] == ':')) {