[FFmpeg-devel] [PATCH] avfilter/drawtext: make command processing error-resilient

[Gyan]

At present, if the command args passed to drawtext contain any invalid 
values, ffmpeg may crash or, at best, stop drawing any text.
Attached patch gets the filter to continue with existing parameters, if 
not all of the changes can be parsed or applied. This allows users in 
live processing to correct and resubmit.

Gyan
-------------- next part --------------
From 57cb3a085363602877790945b619c92b0fedddcd Mon Sep 17 00:00:00 2001
From: Gyan Doshi <ffmpeg at gyani.pro>
Date: Fri, 10 May 2019 19:13:33 +0530
Subject: [PATCH] avfilter/drawtext: make command processing error-resilient

Prevents crash or blank-out if new option string contains invalid
values.
---
 libavfilter/vf_drawtext.c | 47 +++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
index cca2cbcb88..b166574d71 100644
--- a/libavfilter/vf_drawtext.c
+++ b/libavfilter/vf_drawtext.c
@@ -862,20 +862,49 @@ static int config_input(AVFilterLink *inlink)
 
 static int command(AVFilterContext *ctx, const char *cmd, const char *arg, char *res, int res_len, int flags)
 {
-    DrawTextContext *s = ctx->priv;
+    DrawTextContext *old = ctx->priv;
+    DrawTextContext *new = NULL;
+    int ret;
 
     if (!strcmp(cmd, "reinit")) {
-        int ret;
+        new = av_mallocz(sizeof(DrawTextContext));
+        if (!new)
+            return AVERROR(ENOMEM);
+
+        new->class = &drawtext_class;
+        ret = av_opt_copy(new, old);
+        if (ret < 0)
+            goto fail;
+
+        ctx->priv = new;
+        ret = av_set_options_string(ctx, arg, "=", ":");
+        if (ret < 0) {
+            ctx->priv = old;
+            goto fail;
+        }
+
+        ret = init(ctx);
+        if (ret < 0) {
+            uninit(ctx);
+            ctx->priv = old;
+            goto fail;
+        }
+
+        new->reinit = 1;
+
+        ctx->priv = old;
         uninit(ctx);
-        s->reinit = 1;
-        if ((ret = av_set_options_string(ctx, arg, "=", ":")) < 0)
-            return ret;
-        if ((ret = init(ctx)) < 0)
-            return ret;
+        av_freep(old);
+
+        ctx->priv = new;
         return config_input(ctx->inputs[0]);
-    }
+    } else
+        return AVERROR(ENOSYS);
 
-    return AVERROR(ENOSYS);
+fail:
+    av_log(ctx, AV_LOG_ERROR, "Failed to process command. Continuing with existing parameters.\n");
+    av_freep(new);
+    return ret;
 }
 
 static int func_pict_type(AVFilterContext *ctx, AVBPrint *bp,
-- 
2.21.0